The Mo-F System 67
2 Molybdenum and Fluorine Older data are given in "Molybdän", 1935, pp. 150/3.
2.1 The Molybdenum-Fluorine System Fig. 38 shows the phase diagram of the Mo-F system at 1 atm pressure and temperatures above 150°C. It results from a eritieal evaluation of the available experimental observations and the results of thermodynamie ealeulations reported up to 1978 [1].
wt % tluorlne Mo 30 50 70 F ~,LI __-L __ L--L~I~~-LI ~I_I~I~I~I~II lZ00 ~ Mo+gas 1100! ZOO
1000 c-
800 I-
1 atm gas c
-2::: 600 I- w 0.. E Mo +MoFl w ~ m u- D ::E 400 I- Fig.38. Phase diagram of the Mo-F 300! 40' system at 1 atm [1]...... Z67! 10'
200 c- u:' MoF4 D + ::E ~:F'L+gas L Mo 16 ~ I Mo 70 80 90 ot % tluorlne
At low temperatures, phase equilibria have been studied in the eomposition range MoFr MoF6 by thermal methods, X-ray diffraetion, and measurements of magnetie sus eeptibility [2]. The study of the system in the MoFrMoFs eomposition range was eomplieated by the small temperature dependenee of the solubility of MoF4 and the diffieulty of reaehing equilibrium. Therefore the speeimens were kept at 100 to 150°C for 10 to 12 h. MoFs also forms a glass. The equilibrium diagram of the MoFrMoFs subsystem, see Fig. 39, p. 68, shows no eompounds. The euteetie is alm ost degenerate, the euteetie temperature is elose to the melting point of MoFs, and the line for the periteetie eomposition of MoF4 is at 300°C [2].
Gmelin Handbook Mo Suppl. Vol. B 5 5·
H. Jehn et al., Mo Molybdenum © Springer-Verlag Berlin Heidelberg 1989 68 The Mo-F System JojrCd9 280 I 1
Fig. 39. The MoFc MoF6 subsystem [2].
Speeimens in the eomposition range MoF5-MoF6 when fused give yellow liquids. Slow eooling leads to their eomplete erystallization but when eooled rapidly they form glasses. The MoF5-MoF6 equ;librium diagram (see Fig.39) reveals a simple euteetie system with the euteetie point at 6SC, 85.0 wt% MoF6, and with a line of the polymorphie transition of MoF6 at -10.5°C throughout that range of eomposition [2]. In an earlier study of the MoF5-MoF6 subsystem the formation of two eompounds MoF5 • MoF6 and MoF5 • 3 MoF6 and the simulta neous presenee of a line of polymorphism throughout the whole eomposition range has been stated [3]. However, fram equilibrium investigations of the MoF5-MoOF4 system (see Fig. 50, p. 204) and magnetie suseeptibility measurements in the MoF4-MoF5 subsystem it was shown (for diseussion see the paper) that this eontradietory result was obviously eaused by the presenee of small amounts of MoOF4 impurity whieh signifieantly affeet the strueture of the MoF5-MoF6 diagram [2].
The eritieal evaluation of the data of [4, 5] show that for liquid MoF5 with an exeess of MoF4 over MoF6 the relationship ln(p[MoF61· x) = 5.827 - 6400fT ± 0.03 holds in the range 340 to 540 K (p[MoF6] in atm, x in mole fraetion of MoF4) [1].
The 1-atm gas in equilibrium with MoF3(s) and Mo(s) at 1100 ±1 OO°C is ealeulated to eontain 75±5mol% MoF4(g) and 20±2mol% MoF5(g) as shown in Fig.40. Eaeh of MoF6(g) and Mo2F,o(g) is ealeulated to be 3 ± 2 mol%. These speeies are not shown in Fig.40 whieh
1.0,------,
::: ~ 0.6 ::> V> V> ~ 04 Fig. 40. Composition of molybdenum fluorine 1-atm gas in equilibrium with solid molybdenum [1].
2000 2500 T In K
Gmelin Handbook Mo Suppl. Vol. B 5 Molybdenum Fluorides 69
indicates the variation with temperature of the gaseous species MoF2, MoF3, MoF4, and MoF5 in the 1-atm gas in equilibrium with molybdenum metal. MoF4 is seen to be the major species over a wide temperature range. MoF does not become significant until higher temperatures in the liquid molybdenum range [1].
References: [1] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980]195/356, 241/4). [2] Khaldoyanidi, K. A.; Yakovlev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981] 3067/9; Russ. J. Inorg. Chem. 26 [1981] 1639/40). [3] Popov, A. P.; Tsvetnikov, A. K.; Goncharuk, V. K. (Zh. Neorgan. Khim. 23 [1978]236/9; Russ. J. Inorg. Chem. 23 [1978] 132/3). [4] Krause, R. F., Jr. (Proc. Electrochem. Soc. 78-1 [1978]199/209; C. A. 89 [1978] No. 66346). [5] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977] 1149/63).
2.2 Molybdenum Fluorides Survey. Stable fluoride phases exist for molybdenum in each of the oxidation states 3 through 6. The hexafluoride is known since 1905 when it was prepared for the first time by the direct combination of the elements, cf. "Molybdän", 1935, pp. 150/1. The existence of a stable molybdenum trifluoride was for a long time in doubt. The pure compound was obtained for the first time in 1949 by reacting the tribromide with HF at high temperatures. In 1957, MoF4 and MoF5 have been isolated from the product of the reaction between MO(CO)6 and fluorine. Fluorides MoF n with n ~ 2 are metastable. The existence of a fluoride of composition M02Fg as an individual phase could not be confirmed.
At room temperature, MoF3, MoF4, and MoF5 are sOlids, whereas MoF6 forms a colorless liquid above ~17°C. Studies of the physical and chemical properties were complicated by the high sensitivity of the fluorides to traces of water resulting in the formation of oxide fluorides. Even very small amounts of the oxide fluorides affect the properties and lead to wrong conclusions; e. g., a wrong melting point for MoF5 and the apparent existence of MoF4-MoF5 phases were simulated by oxide fluoride contaminations.
2.2.1 Molybdenum Fluorides MoFn with n~1
Solid fluorides MoF n with n ~1 have been found to form (in addition to MoF3) when molybdenum metal was exploded by electric discharge in gaseous PF5 at 515 Torr. The relative proportions of lower fluorides and MoF3 in the reaction products depend strongly upon the imparted electric energy, e. g. at 840 J imparted energy about 54% of the exploded metal has been converted to lower fluorides of composition MoFo.33 to MoFo4g . At an energy of 530 J the solid, insoluble (hot concentrated NaOH solution) residues formed besides traces of MoF3 have empirical formulas MoFo74 to MoF1.00• At higher energy levels MoF3 forms at the expense of the lower fluorides, thus at 2190 J only 19% of the metal was converted to an insoluble residue of empirical composition MoFo.25• It was assumed that the MoFn products were mixtures of noncrystalline MoF with molybdenum fluorides of very low fluorine content [1]. Undoubtedly these phases are metastable [2].
Gmelin Handbook Mo Suppl. Vol. B 5 70 Molybdenum Fluorides
References: [1] Johnson, R. L.; Siegel, B. (J. Inorg. Nucl. Chem. 31 [1969] 955/63, 958, 960). [2] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue NO.7 [1980]195/356, 241).
2.2.2 Molybdenum(1) Fluoride MoF The gaseous species MoF (in addition to higher fluorides) has been detected by high temperature mass spectrometry in the effusion beams generated by the reaction of molybde num wire with MoF6 at 1700 K and with SF6 at 1500 to 2000 K [1,6], see also p.169. The following gives (estimated) molecular constants and (mostly estimated) thermo dynamic properties of gaseous MoF. The Mo-F distance in the molecule is assumed as r=1.84 [1] or 1.89A [2] resulting in moments of inertia (in 10-40 g. cm2) of 89.2 [1] and 93.9 [2], respectively. The vibration frequency of the Mo-F bond is estimated at 700 [1] and 645 [2] cm-1. For the electronic ground state a quartet is assumed in [2], while a doublet is assumed in [1]. The effective charge q on the Mo atom has been calculated in [3] by the method given in [4]. For r =1.84 and 1.89 A, q = 0.85 e and 0.83 e, respectively [3]. By multiple scattering Slater exchange calculations, the electron affinity, EA, and the ionization potential, IP, of the molecule have been calculated. Disregarding spin pOlarization, self-consistent field Hartree-Fock-Slater calculations yield IP = 6.80 and 6.84 eV for quartet and doublet states, respectively, and EA=0.14 eV. With spin polarization included into the calcula tions, IP = 7.55 eV and EA=1.51 eV for the doublet and IP = 7.69 eV for the quartet state [5]. The standard enthalpy of formation of gaseous MoF was determined from gas phase equilibria in the MoF6-Mo and SF6-Mo systems; i1H,,29S(MoF, g) = + 65.0 ± 2.2 kcaUmol [1,6]. From these equilibria the bond dissociation energies D29S(Mo-F) = 111 kcaUmol [1,6] and Dg(Mo-F) =110.3 ± 2.2 kcaUmol have been derived [1]. The heat of dissociation is estimated at 120 kcaUmol (based on a review of literature data) [8]. The standard entropy at 298 K is given as 58.86 cal' mol-1. K-1. Between 400 and 5000 K the esti mated Sr ranges from 61.24 to 83.41 cal· mol-1 . K-1 [2]. The free energy function - (F-H29S)IT (in cal' mol-1. K-1) has been estimated at 56.7 for 298 K, and for 400 to 2400 K it is estimated to range from 57.0 to 67.0 [1]. Mainly based on [1], the following estimates have been given in [7]:
Tin K Cp in cal· mol-1. K-1 W- H29S So in cal·mol-1·K-1 -(Go- H29S)IT in in caUmol cal·mol-1·K-1 298.15 7.78 0 58.85±2 58.85 500 8.39 1641 63.04 59.79 [500 K steps] 3000 10.41 24410 78.98 70.88 The following approximations are given in [7]:
C~R = 4.172 + 2.1 x 10-4T - 28 700r2+ 2.24 x lO-sT2 ± 0.3 -(Go- H29S)/(RT) =4.172 x InT -16000r2+1350r1 +1.460To+1.10 x10-4T +3.7 xlO-9 T2 ±1 (H 29S - Hg)/R = 1079 ±1 0 K [7]. For Mo(s)+0.5 F2(g)~MoF(g), i1Hm/R=(34000±1500) K is given in [7]; also see [9].
GmeLin Handbook Mo Suppt. Vot. B 5 MoF, MoF2 71
For further thermodynamic estimates, see [2,9,10]. For a compiLation of thermochemicaL data, aLso see [11]. Gaseous reaction equiLibria invoLving MoF have been studied by mass spectrometric anaLysis of the effusing vapor generated from the reaction of Mo with SF6 at temperatures between 1818 and 2242 K. The reaction enthaLpies for MoF + S ~ Mo + SF, ßH'29s = 29.2 and 29.3 kcaUmoL, are derived by the second and third Law methods, respectiveLy. EquiLibrium constants are Listed in [1].
References: [1] HiLdenbrand, D. L. (J. ehem. Phys. 65 [1976] 614/8). [2] GaLkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Termodinamicheskie Svoistva Neorga nicheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [3] Pervov, V. S.; FaL'kengof, A. T.; Murav'ev, E. N. (Koord. Khim. 5 [1979] 155/8; Soviet J. Coord. Chem. 5 [1979] 117/20). [4] J0rgensen, C. K.; Horner, S. M.; HatfieLd, W. E.; Tyree, S. Y. (Intern. J. Quantum Chem. 1 [1967] 191/215). [5] Preston, H. J. T.; Kaufman, J. J. (Intern. J. Quantum Chem. 12 [1977] 471/84). [6] HiLdenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63). [7] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980] 11/191, 48). [8] Feber, R. C. (LA-3164 [1964]1/187, 178; C.A. 63 [1965] 9124). [9] Brewer, L. (Proc. ELectrochem. Soc. 78-1 [1978]177/86,179; C.A. 89 [1978] No. 169996). [10] Dittmer, G.; Niemann, U. (Mater. Res. BuLl. 18 [1983] 355/69, 363).
[11] Chase, M. W., Jr.; Davies, C.A.; Downey,J. R.,Jr.; Frurip, D.J.; McDonaLd, R. A.; Syverud, A. N. (JANAF ThermochemicaL TabLes, 3rd Ed., Pt. 11, MidLand, Mich., 1985/86, p. 1032).
2.2.3 Molybdenum(ß) Fluoride MoF2 There is no evidence for the existence of asolid difLuoride of moLybdenum. AUempts to prepare the compound by the reaction of the dibromide with HF at 500 to 800°C were unsuccessfuL [14]. No fluorides of moLybdenum with oxidation state Less than 3 have been produced by disproportionation of higher moLybdenum fluorides upon heating up to 700°C in a Knudsen ceLl [15] or by the reduction of MoF3 with H2 at 300 to 800°C [16] or 500 to 900°C [17]. No significant reduction of MoF3 to Lower fluorides was detected when MoF3 was treated with moLybdenum at temperatures up to 850°C [18]. For a crystaLLine fluoride of bivaLent moLybdenum the crystaL fieLd stabiLization energy ßo = 285, the LaUice energy U = 2979 kJ/moL, and the effective LaUice energy U + ß o = 3113 kJ/moL at 25°C have been estimated [19].
The gaseous species MoF2 (in addition to higher fluorides) has been detected by high temperature mass spectrometry in the effusion beams generated by the reaction of moLybde num wire with MoF6 at 1700 K and with SF6 at 1500 to 2000 K [3,7]. see aLso p. 169.
The point group assumed for the moLecuLe is C2v [1] (symmetry number: 2 [3]). NegLecting any repuLsion between the F Ligands, the F-Mo--F angLe 8 will be cLose to 90° [2]; 8 = 95° was assumed by [1]. However, 8=160° was estimated by [3]. The Mo--F distance was estimated at r = 1.84 [3] and 1 .87 A [1]. Fo r the moments of inertia Ix, Iy' and Iz (i n 10-39 9 . cm 2) the values 0.462, 20.7, and 21.2, respectively, are derived (resulting in Ix·ly·lz= 2.0274 x 10- 115 g3. cm6) [3]; Ix·ly·'z=1.6558XlO-115g3. cm 6 is given in [1].
Gmelin Handbook Mo Suppt. Vol. B 5 72 Mo~bdenum Auorides
For the fundamental vibrations, frequencies of 273, 591, and 620 cm-1 are assumed in [1], while 150 cm-1 (ix) and 700 cm-1 (2x) are estimated by [3]. The electronic ground state is assumed to be a singlet [1,3]. Using the method given in [4] the effective charge q (in e) on the Mo atom was calculated for r=1.84 Aas 0.98, 0.96, 0.92, and 0.77 for e =180°, 140°, 120°, and 95°, respectively [5].
On successively cleaving the Mo-F bonds in MoFn, the maximum energy in this series is required at n = 2, see [6]. The bond dissociation energy at 298 K is D298 (F-MoF) =124 kcaUmol according to studies of gas phase equilibria [3, 7]. In an evaluation of literature data, the heat of dissociation of gaseous MoF2 is estimated at 264 kcaUmol in the review [8]. For gaseous MoF2, the calculated C~ (in ca!' mo!-l. K-l) is 13.68 at 298.15 K and ranges from 14.45 to 14.89 between 500 and 3000 K [9].
ÖG~8/(RT)=-70.6±7 [9], also see [10]. For -(Go-H~8)IT the values (in cal·mol-1 ·K-1) 64.97 for 298.15 K and 66.55 to 85.44 for 500 to 3000 K were estimated [9]. Similarly, for - (Go-Hg)IT the values 57.21 for 298.15 K and 60.11 to 91.13 for 400 to 5000 K were estimated [1]. For estimated -(F-H298)IT values (T=298 to 2400 K), see [3].
The standard entropy of gaseous MoF2 is S~8 = 66.69 [1] or 64.97 ± 2 [9] cal· mol-1 • K-1. S~alR = 32.7 ±1 [9, 10]. The estimated So values (in cal· mol-1 • K-l) range from 70.25 to 104.53 between 400 to 5000 K [1] or from 72.27 to 98.74 between 500 and 3000 K [9]. The enthalpy of formation of gaseous MoF2 was derived from gas phase equilibria in the Mo-SF6 and Mo-MoF6 systems; ÖHf.298[MoF2(g)] =- 40.2 ± 2.9 kcaUmol [3, 4]. In the review [9], ÖH 29a1R =-19600 ± 2000 K is given; also see [10]. HO-H~8 = 2.86 to 39.9 kcaUmol for T= 500 to 3000 K [9]. For a compilation of thermochemical data of MoF2(g), also see [20]. With a view to isotopic exchange equilibria, the ratio of the partition functions of isotopic MoF2 molecu!es have been calculated for 300 K [13]. For the hypothetical crystalline MoF2, ÖHf.298[MoF2(s)] = -170 ± 15 kcaUmol (~711 kJ/mol) [11] and -1415 kJ/mol [12] have been estimated. Similarly, S~8= 25 ± 2 cal' mol-1 • K-1 (~105 J. moL-1. K-l) [11] and 62 J. mol-1 • K-l [12] have been estimated for the solid for which C~.298 =83.7 J. mol-1 • K-1 and the entha!py of sublimation ÖH~Ub.298 = 363 kJ/mol have been estimated [12].
A thermodynamic anaLysis of the hypothetical reaction MoF2(s) + H2(g) ~ Mo(s) + 2 HF(g) as a thinkable step in the hydrogen reduction of MoFs (see p. 166) was presented in [17] but the reaction was found to be impossibLe.
The gas-phase reaction MoF + MoF3~2 MoF2 was studied by mass spectroscopy between 2054 and 2230 K of the Mo + SFs system. The equitibrium constants found are:
K 4.15 3.86 3.87 3.89 3.83 4.22 Tin K ...... 2054 2100 2140 2161 2178 2230 The enthalpies of reaction ÖH 298 derived therefrom by second and third law evaluation (using ÖW= T[ÖSO- R ln K] or - R[d ln Kld(r1)]) are 0.3 and -5.3 kcaUmol, respectively. The third law evaLuation of data collected in the Mo + MoF6 system at 2071 to 2171 K yieLds öH = - 5.6 kcaUmot. At temperatures between 1818 and 2242 K, the reaction enthalpies for MoF2+ S ~ MoF + SF, ÖH 298 = 42.1 and 44.0 kcaUmol, were derived by the second and third law methods, respective ly. Equitibrium constants are listed in [3].
Gmelin Handbook Mo Suppl. Vol. B 5 73
References: [1) Galkin, N. P.; Tumanov, Yu. N.; Butylki.n, Yu. P. (Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [2) Charkin, O. P.; Dyatkina, M. E. (Zh. Strukt. Khim. 6 [1965)579/90; J. Struct. Chem. [USSR) 6 [1965) 550/60). [3) Hildenbrand, D. L. (J. Chem. Phys. 65 [1976) 614/8). [4) JeJrgensen, C. K.; Horner, S. M.; Hatfield, W. E.; Tyree, S. Y. (Intern. J. Quantum Chem. 1 [1967) 191/215). [5) Pervov, V. S.; Fal'kengof, AT.; Murav'ev, E. N. (Koord. Khim. 5 [1979)155/8; Soviet J. Coord. Chem. 5 [1979)117/20). [6) Pervov, V. S.; Fal'kengof, A. T.; Murav'ev, E. N. (Koord. Khim. 4 [1978)1828/34; Soviet J. Coord. Chern. 4 [1978)1400/5). [7) Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981) 357/63). [8) Feber, R. C. (LA-3164 [1964)1/187; C.A 63 [1965) 9124). [9) Brewer, L.; Larnoreaux, R. H. (At. Energy Rev. Spec.lssue No. 7 [1980)11/191,46,48). [10) Brewer, L. (Proc. Electrochern. Soc. 78-1 [1978)177/86; C.A 89 [1978) No. 169996).
[11) Rychagov, A. V.; Korolev, Yu. M.; Bratishko, V .. D.; Rakov, E. G. (Tr. Moskovsk. Khirn. Tekhnol. Inst. No. 62 1969 52/6). [12) Dittrner, G.; Niemann, U. (Mater. Res. Bull. 18 [1983) 355/69). [13) Knyazev, D. A; Ivlev, A. A.; Popov, I. B. (Zh. Fiz. Khirn. 43 [1969)1269/78; Russ. J. Phys. Chern. 43 [1969) 704/8). [14) Erneleus, H. J.; Gutmann, V. (J. Chern. Soc. 1949 2979/82). [15) Weaver, C. F.; Friedrnan, H. A. (ORNL-4449 [1970)113/5). [16) Rychagov, A V.; Korolev, Yu. M. (Zh. Neorgan. Khirn. 23 [1978) 263/5; Russ. J. Inorg. Chern. 23 [1978) 149/50). [17) Kopchikhin, D. S.; Rychagov, A. V.; Korolev, Yu. M.; Rakov, E. G. (Tr. Inst. Mosk. Khirn. Tekhnol. Inst. No. 62 [1969) 60/2; C.A 75 [1971) No. 80810). [18) Fukutorni, M.; Corbett, J. D. (J. Less-Cornrnon Metals 55 [1977)125/30). [19) Thakur, L.; Sandwar, B. B. (Indian J. Pure Appl. Phys. 18 [1980) 360/1). [20) Chase, M. W., Jr.; Davies, C. A.; Downy, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, AN. (JANAF Therrnochernical Tables, 3rd Ed., Pt. 11, Midland, Mich., 1985/6, p. 1082).
2.2.4 Molybdenum(lD) Fluoride MoF3 Older data are given in "Molydän", 1935, p. 150. Remarks. The solid rnolybdenurn trifluoride has been prepared for the first time in 1949 [1). The crystallographic data wh ich were obtained with preparations slightly contarninated by oxy~en (see p. 77) led to the speculation that MoF3 could be obtained only as a rnetastable phase under special conditions but is stabilized by partial replacernent of fluorine by oxygen [2,3). It is now weil established that the pure cornpound exists as a stable phase at roorn ternperature and rarnains unchanged in air over periods of rnany days [4). Note, that various colors have been indicated for different MoF3 sam pIes prepared. For an explanation for sorne of thern see p. 80.
References: [1) Erneleus, H. J.; Gutmann, V. (J. Chern. Soc. 19492979/82). [2) Schäfer, H.; Schnering, H. G.; Niehues, K.-J.; Nieder-Vahrenholz, H. G. (J. Less-Cornrnon Metals 9 [1965) 95/104, 100).
Gmelin Handbook Mo Suppt. Vot. B 5 74 MoLybdenum Fluorides
[3] Hoppe, R.; Lehr, K. (Z. Anorg. ALLgem. Chem. 416 [1975] 240/50, 246/8). [4] Fukutomi, M.; Corbett, J. D. (J. Less-Common Metals 55 [1977] 125/30).
2.2.4.1 Preparation. Formation The compound was first obtained as a dark pink powder by reacting moLybdenum tribromide with HF at 600°C (about 7 h) in a pLatinum boat encLosed in a copper tube. As the reaction was hindered by the formation of a coating over the solid MoBr3 the process was interrupted for grinding the product. With pure starting materiaLs the yieLd was 95% [1]. An attempt to prepare MoF3 by the same reaction via the intermediate MoBr3 produced from the eLements, was unsuccessfuL [5]. The fLuorination of metallic moLybdenum with fLuorine at atmospheric pressure yieLds a mixture of binary fluorides of moLybdenum in different oxidation states. From this mixture, MoF6 can be removed by sublimation at 35 to 45°C. The MoF5 and MoF4 are removed with a stream of purified H2 at temperatures between 250 and 300°C. The residuaL paLe brown powder is identified as MoF3 [6]. From the eLements Light yeLLow trifluoride can aLso be obtained in a bomb reaction at 200 atm and 400°C (105 min) when Mo is in excess (Mo: F = 2.5:1) and fLuorine is diLuted with dry argon. In the autocLave, the temperature is 400°C at the bottom and 100°C at the top. The MoF3 covers the remaining Mo metaL whiLe crystaLLites of moLybdenum occur at the top and MoF5 separates at the bottom. With Longer reaction periods, MoF3 disappears, even in the presence of unreacted moLybdenum [3]. When Mo powder is treated with Liquid HF at 225 ± 5°C in a cLosed system so me MoF3 is produced. However, fLuorination of Mo is incompLete within 24 h [7].
"Pure" (e.g. Lemon yeLLow) MoF3 can be prepared by the reduction of a stream of gaseous MoF6 in Ar by Mo in an InconeL container. The reaction tube is Loaded so that on entry the MoF6 reacts first with hydrogen-reduced Mo powder in an Mo boat. This is foLLowed by many smaLL sheets of Mo foiL. Quantitative reduction is achieved at a fLow rate of 60 mUrnin when the Mo powder is heLd at 550°C and the foiL at 600°C by an externaL furnace. The coLor of the preparations vary with increasing temperature from Lemon yeLLow (400°C), to gray-green (700°C), Light brown (750°C), and dark red (850°C). At Lower temperatures the product is contaminated with MoF4 [4]. With moLybdenum in the form of incandescent fiLaments the MoF6 is reduced at fiLament temperatures of 600 to 800°C and MoF6 pressures of 0.6 to 0.8 atm. The MoF3 deposits on the reaction vesseL walls which are cooLed to 200 to 300°C. It can be purified by thermaL treatment at 400°C in a dynamic vacuum [9,10]. For the simuLtanElous preparation of MoF3 and MoF5, purified MoF6 is refLuxed with a predetermined quantity of pure Mo metaL to obtain a soLution of MoF5 in MoF6. After compLete reaction of the added moLybdenum the system is evacuated and sLowLy heated to a finaL temperature of 200°C. The MoF3 remains as a tan residue in the buLb of the pyrex fLask whiLe gaseous MoF6 Leaves the equipment and MoF5 subLimes to the cooLer neck of the reaction vesseL where it forms a yeLLow deposit [11]. The reduction of MoF5 with Mo is achieved with a 50% excess of MoF5 by heating the mixture in a vacuum at 180°C for 2 hand then at 400°C for 2 h. The excess MoF5 is removed by distiLLation. The MoF3 obtained by this method has been observed in coLors ranging from ochre through Light green and gray depending on detaiLs of preparation. UsuaLLy a yeLLowish tan-coLored MoF3 is obtained. If this is heated in seaLed evacuated Ni tubes at 800°C it is bLack, but when it is heated at 900°C (16 h), a dark red sharpLy crystaLLine MoF3 is obtained [12]. MoF4 can be reduced with metallic moLybdenum at 400 to 410°C (6 h) in a vacuum. Subsequent vacuum heat treatment of the resuLting product yieLds MoF3 with 99.5 to 99.7% purity [13].
By reacting an Mo incandescent fiLament with NF3 (0.2 to 0.4 atm) at 350 to 400°C, MoF3 is deposited as the soLe solid reaction product on the reaction vesseL walls which are cooLed to
Gmelin Handbook Mo Suppl. Vol. B 5 75
100 to 150°C. AdditionaL purification is not necessary [10]. The formation of MoF3 as an intermediate during the fLuorination of Mo by NF3 at 280°C, has been reported in [14]. With CF4 (0.5 to 0.8 atm) and Mo fiLament temperatures 1200 to 1500°C, MoF3 separates together with MoF4 at 100 to 150°C [10].
Disproportionation of MoFs in a vacuum at 200°C yieLds MoF3 as the solid residue when the gaseous reaction product, MoF6, is removed by pumping [15]. SimiLarLy, MoF4 decomposes to MoF3 and MoF6 on sLowLy heating to 250°C whiLe maintaining the pressure in the 10-3 Torr region [16].lt is said that MoF3 isaLsoobtained by heating a mixtureof MoFsand MoF4 at 400°C in a "dynamic" vacuum [10].
MoF3 can be produced in good yieLd by eLectroLyzing an aqueous 40% HF soLution with a consumabLe Mo anode at 0.10 to 0.15 Ncm2 current density for 6 hand then mixing the resuLtant soLution with pyridine at moLar ratios Mo:pyridine=1:4.5 to 1:6. The mixture is evaporated to precipitate an anhydrous pyridine fluoro compLex. VoLatiLe products are re
moved at 20°C, 10-2 Torr (8 h). Heat treatment at 450°C (6 h) yieLds MoF3 by decomposition of the compLex [17].
The trifluoride torms as an intermediate during the reduction of MoF6 with hydrogen, see p. 166. BLack MoF3 is obtained when MoFs is reduced with excess SbF3 in a stream of Ar at 150 to 200°C [12]. The fLuorination of MoN with NF3 at 260°C to produce MoF6 was found to proceed via MoF3 [14]. ELectric expLosion of Mo metaL into PFs Leads to the formation of MoF3 in addition to Lower fluorides when the imparted energy is ~840 J [18].
Gaseous MoF3 has been detected by high-temperature mass spectrometry in the effusion vapor generated by reacting moLybdenum with SF6 [2,8] or MoF6 at temperatures above 1000°C [2].
References: [1] EmeLeus, H. J.; Gutmann, V. (J. Chem. Soc. 19492979/82). [2] HiLdenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [3] Hoppe, R.; Lehr, K. (Z. Anorg. ALLgern. Chem. 416 [1975] 240/50, 246/8). [4] Fukutomi, M.; Corbett, J. D. (J. Less-Common Metals 55 [1977] 125/30). [5] Brady, A. P.; CLauss, J. K.; Myers, O. E. (WADC-TR-56-4 [1955]1/55,4; N.S.A. 10 [1956] No. 7512). [6] Rychagov, A. V.; KoroLev, Yu. M. (Zh. Neorgan. Khim. 23 [1978] 263/5; Russ. J. Inorg. Chem. 23 [1978]149/50). [7] Muetterties, E. L.; CastLe, J. E. (J. Inorg. Nu cl. Chem. 18 [1961]148/53). [8] HiLdenbrand, D. L. (NucL. Instrum. Methods Phys. Res. 186 [1981] 357/63, 359). [9] ALikhanyan, A. S.; StebLevskii, A. V.; MaLkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, pp. 1/29; C.A. 90 [1979] No. 29936). [10] ,Pervov, V. S.; Butskii, V. D.; PodzoLko, L. G. (Zh. Neorgan. Khim. 23 [1978]1486/91; Russ. J. Inorg. Chem. 23 [1978] 819/22).
[11] Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4229 [1968] 33/7; N.SA 22 [1968] No. 25374; ORNL-4254 [1968]129/34). [12] LaVaLLe, D. E.; SteeLe, R. M.; WiLkinson, M. K.; YakeL, H. L., Jr. (J. Am. Chem. Soc. 82 [1960] 2433/4). [13] OpaLovskii, A. A.; Fedorov, V. E.; KhaLdoyanidi, K. A. (U.S.S.R. 263581 [1968/72]; C.A. 78 [1973] No. 6039). [14] GLemser, 0.; Wegener, J.; Mews, R. (Chem. Ber. 100 [1967] 2474/83, 2478/9). [15] Weaver, C. F.; Friedman, H. A. (ORNL-4191 [1967]142/3).
GmeLin Handbo0k Mo Suppl. Vol. B 5 76 Molybdenum Fluorides
[16] Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970]113/5). [17] Mazhara, A. P.; Evstafev, V. K.; Fedorov, V. E. (U.S.S.R. 815086 [1979/81]; C.A. 94 [1981] No. 216631). [18] Johnson, R. L.; Siegel, B. (J. Inorg. Nucl. Chem. 31 [1969] 955/63, 958, 960).
2.2.4.2 The Moleeules MoF3 and Mo2F6 The MoF3 monomer in the gas phase is assumed to be pyramidal with an F-Mo-F angle of 100° [1]; symmetry number: 3 [2]; point group: C3V [3]. A flat configuration with point symmetry D3h was also considered [3,7].
The vibrational modes have estimated frequencies of 300, 600, 250, and 650 cm-1 with degeneracies of 1, 1, 2, and 2, respectively [1,2]. 309, 670, 243, and 624 cm-1 are the corresponding estimates for C3v. With the same degeneracies the frequencies 602,195,183, and 687 cm-1 have been estimated for D3h geometry [3].
Assumed Mo-F distances are r= 1.82 [1], 1.84 [2], and 1.86 A [3]. The moments of inertia (in 10-40 g·cm2) are estimated at 169, 169, and 251 for Ix, Iy' and Iz, respectively [2]. For a compilation of molecular data of MoF3 see [14].
For the Mo2F6 molecule the structural parameters have been calculated using Slater type orbital wave functions approximated bya linear combination of three Gaussians. The follow ing parameters result for staggered and eclipsed conformations:
conformation r(Mo-Mo) in A r(Mo-F) in A For the M02F6~2MoF3 gas phase equilibrium studied by mass spectrometry, the standard enthalpy of reaction, ßH2sB = 52.8 ± 5.5 kcaUmol, was derived assuming an entropy of reaction ßS=37±4 cal· mol-1 ·K-1 [8]. From a review of literature data, the dissociation energy of gaseous MoF3 is estimated at 388 kcaUmol [9]. The bond dissociation energy D29B (F2Mo-F) =120 kcaUmol is derived from a study of gas phase equilibria [2, 12]. For the MoF3 monomer the electronic ground state is assumed to be a singlet [2]. In the thermodynamic calculations by [1,4] cited below, the electronic contribution to the partition function is taken from the "isoelectronic" TaO [1]. Optical spectra of the solid have been interpreted assuming a quartet ground state (see below) [5]. The charge on the Mo atom has been calculated for the monomer (r = 1.84 A; D3h) as 0.81 e [7] (using the theory given in [10]). The ionization potentiallP = 10.2 ± 0.5 eV was determined in the mass spectrometric study [11] for the reaction MoF3-. MoF~ + e-. For the ionization accompanied by a loss of a fluorine atom, MoF3-. MoFt+ F + e-, the IP= 14.3 ± 1 eV [11]. The electron affinity EA(MoF3) has been estimated to be <3.3 eV [13]. Gmelin Handbook Mo Suppl. Vol. B 5 77 The mass spectrum of MoF3 moLecuLes bombarded by 72 eV eLectrons is as foLLows [11): species ...... MoFt MoF~ intensity 150±50 100 a) assumed vaLue References: [1) Brewer, L. (Proc. ELectrochem. Soc. 78-1 [1978)177/86,182/4; C.A. 89 [1978) No. 169996). [2) HiLdenbrand, D. L. (J. Chem. Phys. 65 [1976) 614/8). [3) GaLkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Termodinamicheskie Svoistva Neor- ganicheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [4) Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980)11/191,49). [5) Hoppe, R.; Lehr, K. (Z. Anorg. ALLgem. Chem. 416 [1975) 240/50). [6) Dobbs, K. D.; FrancL, M. M.; Hehre, W. J. (lnorg. Chem. 23 [1984) 24/6). [7) Pervov, V. S.; FaL'kengof, A. T.; Murav'ev, E. N. (Koord. Khim. 5 [1979) 155/8; Soviet J. Coord. Chem. 5 [1979)117/20). [8) ALikhanyan, A. S.; Pervov, V. S.; MaLkerova, I. P.; Butskii, V. D.; Gorgoraki, V.I. (Zh. Neorgan. Khim. 23 [1978)1483/5; Russ. J. Inorg. Chem. 23 [1978) 817/8). [9) Feber, R. C. (LA-3164 [1964)1/187, 178; C.A. 63 [1965) 9124). [10) J0rgensen, C. K.; Horner, S. M.; HatfieLd, W. E.; Tyree, S. Y. (Intern. J. Quantum Chem. 1 [1967) 191/215). [11) ALikhanyan, A. S.; StebLevskii, A. V.; MaLkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V.I. (Zh. Neorgan. Khim. 23 [1978)1477/82; Russ. J. Inorg. Chem. 23 [1978) 814/7). [12) HiLdenbrand, D. L. (NucL. Instrum. Methods Phys. Res. 186 [1981) 357/63). [13) Sidorov, L. N.; Borshchevsky [Borshchevskiij, A. Ya.; Rudny [Rudnyi), E. B.; Butsky [Butskiij, V. D. (Chem. Phys. 71 [1982)145/56). [14) Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonaLd, R. A.; Syverud, A. N. (JANAF ThermochemicaL TabLes, 3rd Ed., Pt. 11, MidLand, Mich., 1985/86, p. 1121). 2.2.4.3 Crystallographic Properties The crystaL structure of MoF3 has been described as cubic, space group Pm3m-O~ (No.221) (Re03 structure, D09 type) [1 to 4) and rhombohedraL, space group R3c-D~d (No. 167) (VF3 type, see "Vanadium" B1, 1967, p. 182) [5 to 7). There is evidence that the compound does not exist in two crystaLLine modifications, but that the cubic structure is simuLated by impurities known to give refLections of a cubic Re03-type phase, e.g. moLybde num oxide fluorides. It was shown that sampLes of the cubic structure were obtained onLy when smaLL amounts of moisture, quartz, or oxygen were present in the system [5). The Lattice parameter of MoF3 (prepared according to [1 J) was found from X-ray powder diffraction data as a = 3.8995 ± 0.0005 A [2) and depending on the preparation conditions, between 3.96 and 4.01 A, which might be an effect of oxygen impurities. However, by chemicaL anaLysis onLy very smaLL amounts of oxygen were found [4). X-ray and neutron powder diffraction data of the pure compound have been indexed on the basis of the rhombohedraL unit ceLL of the VF3-type structure [5 to 8). Lattice parameters are a=5.666±0.001A, a=54°43'±10'; Z=2. For the corresponding hexagonaL ceLL a= GmeLin Handbook Mo Suppt. Vot. B 5 78 Molybdenum Fluorides 5.208 ± 0.001 , c = 14.409 ± 0.01 0 A. The value of the free parameter of the fluorine, x=-0.12±0.01, was determined from neutron diffraction data (6F in 6e: ±(x, 0.5-x, 0.25); ±(0.5-x, 0.25, x); ±(0.25, x, 0.5-x)), while Mo is placed in 2b (0, 0, 0; 0.5, 0.5, 0.5) [5). A slight increase of the lattice parameters from a = 5.2034(4), c =14.394(2) to a = 5.2138(6), c=14.415(2) A was measured, when bright yellow or gray-green MoF3 was equilibrated with Mo at 850°C for 7 d, albeit the chemical composition of the samples did not change [6). A list of 2 evalues from an X-ray powder pattern wh ich corresponds to the lattice parameters of [5) is given in [9). A Debye temperature of 280±25 K was determined from the temperature dependence of the (110), (210), and (321) nuclear Bragg peaks observed by neutron powder diffraction between 4.2 and 425 K. A powder diagram taken at 4.2 K is displayed in [8). Lattice self-potentials U and the Madelung constants have been calculated [10) assuming the (obsolete) Re03-type cubic structure given in [11). For the M0 3+ site U =- 2.14 e/Ä, for the F- sites U = 0.96 e/A. The lattice energy is 1543.8 kcaVmol [10). Assuming an Mo-F distance of 1.924 A, the Madelung part of the lattice energy is 1065 kcal/mol for M0 3+ and (3 x) 159.3 kcal/mol for F- [12). References: [1) Emeleus, H. J.; Gutmann, V. (J. Chem. Soc. 1949 2979/82). [2) Gutmann, V.; Jack, K. H. (Acta Cryst. 4 [1951) 244/6). [3) Muetterties, E. L.; Castle, J. E. (J. Inorg. Nucl. Chem. 18 [1961) 148/53). [4) Glemser, 0.; Wegener, J.; Mews, R. (Chem. Ber. 100 [1967) 2474/83, 2478). [5) LaValle, D. E.; Steele, R. M.; Wilkinson, M. K.; Yakel, H. L. (J. Am. Chem. Soc. 82 [1960) 2433/4). [6) Fukutomi, M.; Corbett, J. D. (J. Less-Common Metals 55 [1977) 125/30). [7) Wilkinson, M. K.; Wollan, E. 0.; Child, H. R. (Bull. Am. Phys. Soc. [2) 4 [1959) 242). [8) Wilkinson, M. K.; Wollan, E. 0.; Child, H. R.; Cable, J. W. (Phys. Rev. [2)121 [1961)74/7). [9) Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4229 [1968) 33/7; N.S.A. 22 [1968) No. 25374). [10) van Gool, W.; Picken, A. G. (J. Mater. Sci. 4 [1969) 95/104). [11) Wyckoff, R. W. G. (Crystal Structures, Vol. 11, Interscience, New York 1964, p.48). [12) Hoppe, R. (Advan. Fluorine Chem. 6 [1970) 387/438, 396, 412/3). 2.2.4.4 Physical Properties Mechanical and Thermal Properties. The density Dm = 4.64 ± 0.07 g/cm3 has been measu red with tan MoF3 by the gas displacement method (which is slightly biased toward a high result); Dx = 4.50 g/cm3 [11). MeLting. Vaporization. In the absence of air, MoF3 neither melts nor sublimes at tempera tures up to 800°C [13). On heating in a Knudsen cell, MoF3 is not volatile as a pure compound in the range of mass spectrometric operating temperatures (~850°C) [14). The enthalpy of sublimation at 964 K is estimated at 72.0 ± 2.5 kcal/mol in the mass spectral study; the recalculated standard value ~H~ub.298 = 75.1 ± 3.0 kcal/mol [3). Sublimation and vaporization enthalpies of ~HSUb.298=286 kJ/mol and ~Hvap.298=148 kJ/mol, respectively, have been estimated. Sublimation and vaporization entropies ~Ssub. 298 = 213 J. mol-1. K-1 and ~Svap.298=161 J·mol-1·K-1, respectively, were estimated [7). Gmelin Handbook Mo Suppl. Vol. B 5 MoF3 79 Thermodynamic Data. Heat Capacity. For solid MoF3, C~R =13 + 0.001 T - 500ff2 is as sumed for the range 298 K~T~ 1013 K [5]. For the liquid at 298 K, C~=121 J. moL-1. K-1 was estimated [7]. For gaseous MoF3 between 298 and 3000 K the caLcuLated heat capacity is approximated (to within ± 0.2) by C~R= 9.7487 + 2.97 x10-4 T -159300r2+ 2.15 x10-sT2 [6] revising a Less accurate expression given in [5]. C~ vaLues are listed for 0 to 6000 K in [12]. The Debye temperature 8 = 280 ± 25 K, see p. 78. Entropy. For solid MoF3, S2ooIR=11±2 [5] and S2ss=32±4caL·moL-1·K-1 [8] have been estimated. For the liquid, S2sa=135J·moL-1·K-1 has been estimated [7]. S29s=70.71±2caL· moL-1 . K-1 was estimated for gaseous MoF3 [6]; 71.99 and 71.61 caL· moL-1 . K-1 were caLcuLated assuming D3h and C3v symmetry, respectiveLy [10]. For tabLes of So, for 400 to 5000 K, for both D3h and C3v symmetry, see [10]; for 500 to 3000 K, see [6]; for 0 to 6000 K, see [12]. Other Thermodynamic Functions. FormuLas approximating - (Go-H29S)/RT have been given for solid MoF3 from 298 to 1013 K [5]; for gaseous MoF3 from 298 to 3000 K [5,6] and from 0 to 6000 K [12]. For both C3v and D3h symmetry of the moLecuLe, estimated vaLues of -(Go- Ho)ff are tabulated for gaseous MoF3 at 400 to 5000 K. At 298 K the vaLues are 59.92 (C3V) and 59.63 (D3h) caL'moL-1'K-1 [10]. For estimated va Lues of -(F-H298)ff between 298 and 2400 K, see [1]; for W - H2sS between 0 and 6000 K, see [12]. (H 2sa - Ho)/R = 1768 ± 100 K was assumed for gaseous MoF3 [6]. Thermodynamic Data of Formation. For soLid MoF3, the enthaLpy of formation ~Hf.29S[MoF3(S)]=-217.6±4.7 kcaVmoL [3,4]; -240±15 kcaVmoL were estimated semi empiricaILy [8]. ~Hf.~R=-107150±2000 was assumed from a review of the dispropor tionation of MoF3 [5]. The free energy of formation ~Gf[MoF3(S)] =-185 kcaVmoL was estimated [9]. For the Liquid, ~Hf.29S[MoF3(L)]=-1668 kJ/moL were estimated [7]. The enthaLpy of formation of gaseous MoF3was derived from mass spectrometric studies of gas phase equiLibria invoLving MoF3 [1 to 4]. ~Hf.298[MoF3(g)] = -141.5 ± 3.5 [1,2], -142.5 ± 5.9 kcaVmoL [3,4]. The vaLue ~Hf.29a1R = -71500 ±3000 in [5] is are-evaLuation of the data given in [1]; it was revised into - 73000 ± 2000 in the review [6]. For vaLues of ~Hf' ~Gf' and Log Kt between 0 and 6000 K, see [12]. Magnetic Properties. Susceptibility. Magnetization. The susceptibiLity X of poLycrystalLine MoF3 was measured between 78 and 800 K [15] and between 100.4 and 295.2 K [16] by the Faraday method [15,16]. MoF3 is antiferromagnetic beLow TN =172 K, see Fig. 41, p. 80 [15]. This T N vaLue was confirmed by [16] who found the moLar susceptibility Xm (in 10-6 cm3/moL) to range from 45430 at 100.4 K to 2770 at 295.2 K [16]. This T N vaLue is significantLy Lower than the 185 K deduced from neutron diffraction studies [17 to 20] (that high vaLue might have been suggested by short range order effects). Deviations of X- 1 vs. T from the (linear) Curie-Weiss behavior observed at T~400 K suggest considerabLe antiferromagnetic pre-ordering. Above 400,K, the Curie-Weiss Law X = ~""(3 kB ' [T -8]) is obeyed with 8 = - 200 K and fleff = 3.5 flB [15]. The Low vaLue of 0.53 flB from unpublished work [21] cited in [22] is obviousLy obsolete. BeLow T N the above measurements [15] show a magnetization o(H, T) wh ich is linear in H for fieLds H?;5kOe: o(H,T)=oo(T)+X·H with a nearLy T independent X, see Fig. 41. The weak spontaneous moment oo(T) is weIL represented bya BriLLouin function B3/2(T). The oo(T) curve extrapoLates from 320 G· cm3/moL at 78 K to - 350 G . cm3/moL at T = 0 K. Th is i nd icates that the subLattices deviate from the exact antiparalLel orientation by a canting angLe of -1.2° [15]. The exchange fieLd HE being the ratio of subLattice magnetization Ms to perpendicuLar susceptibility Xl.' HE = Ms/Xl. =2.76 MOe (given as -3 MOe in the paper). The DzyaLoshinskii fieLd HD = HE' oo(O)/Ms = oo(O)/Xl. =60 kOe (given as -70 kOe in the paper) [15]. Gmelin Handbook Mo Suppl. Vol. B 5 80 Molybdenum Fluorides II cl I 6 30D- ~15 0 E ~E ~ 10 200Eu ~ II x 5 100·e= E -0 N ~ 4 E u 50 o E E N N , S' 2 Z46BlO H In kOe 200 400 600 800 Temperature In K Fig.41. Magnetic properties of MoF3. (a) Reciprocal of the molar susceptibility Xm vs. temperature, (b) magnetization 0 VS. field strength at various temperatures, (c) I) spontaneous magnetic mo- ment 0 0 and 11) molar susceptibility Xm VS. temperature [15]. Magnetic Structure. Neutron powder diffraction patterns have been recorded using 1.=1.08 A neutrons in the angular range 2{t=5° to 38° at temperatures between 4.2 and 425 K. Two magnetic Bragg peaks were found at 4.2 K, indexed (111) and (100) in the rhombohedral unit cell, Z = 2, space group R3c. The M0 3+ ions sitting at the corners of a distorted cube are coupled antiferromagnetically (af) to their nearest Mo neighbors (along the cube edges), ferromagnetically (ferro) to their next nearest Mo neighbors (along the face diagonals), and again af to the M0 3+ ion at the opposite end of the cube diagonal [17, 19] (G-type ordering in the nomencLature of [23]). The magnetic moments are cLosely perpendicular to the :3 axis [17, 19] with ferro intraLayer coupling between the M0 3+ ions arranged in the layers perpen dicuLar to the 3 axis and af interLayer coupling [17]. These resuLts obviousLy supersede the paper [18] where an apparentLy incorrect indexing was given. As noted above, the T N =185 K vaLue determined from the Brillouin-type temperature dependence of the (111) Bragg intensity [17, 19] seems to be high by -10%. The magnetic form factor of the 4 d eLectrons of M0 3+ was derived from the diffuse scattering observed at 425 K (with the 4.2 K background substracted). The resuLt was con sistent with spin-only scattering. The amplitude extrapoLated to the forward direction is in good agreement with S=3/2 [17]. OpticaL Properties. Depending on the conditions of preparation (p. 74), the colors of MoF3 have been described to be bright yellow [24, 25], pale brown [26], ochre, light green, gray [11], or dark pink [13]. PaLe yellow preparations obtained from the eLements in a bomb reaction darkened to brownish yeLlow when the autoclave was opened in an atmosphere of argon presumabLy due to traces of O2 in the Ar [16]. Upon equilibration with Mo, the coLor of the MoF3 Gmelin Handbook Mg Suppt. VoL B 5 81 changes to lemon yellow, gray-green, light brown, or dark red, depending on the temperature and time of treatment. The composition of the samples remains almost unchanged [25]. Discoloration to black or dark red was observed when MoF3 was heated in sealed Ni tubes at 800 or 900°C [11]. Using golden yellow MoF3, the refractive indices n.,=1.592 and n.=1.624 were found in a study of this optically uniaxial positive solid (wavelength not mentioned) [24]. The reflection spectrum between -15000 and -32000 cm-1 is plotted in [16] forthe yellow solid at room temperature (white standard: MgO). The spectrum shows a shoulder near 17000 cm-1 and peaks at 22000 and 27000 cm-1• The 22000 cm- 1 peak is assigned to a 4T29(t~9' eg)~4A29(t~9) transition [16]. References: [1] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [2] Hildenbrand, D. L. (Nuct. Instrum. Methods Phys. Res. 186 [1981] 357/63). [3] Alikhanyan, A. S.; Pervov, V. S.; Malkerova, I. P.; Butskii, V. D.; Gorgoraki, V.1. (Zh. Neorgan. Khim. 23 [1978]1483/5; Russ. J.lnorg. Chem. 23 [1978] 817/8). [4] Alikhanyan, A S.; Steblevskii, A. V.; Malkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 29; C.A. 90 [1979] No. 29936). [5] Brewer, L. (Proc. Electrochem. Soc. 78-1 [1978]177/86, 182/4; C. A. 89 [1978] No. 169996). [6] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980]11/191,49). [7] Dittmer, G.; Niemann, U. (Mater. Res. Bult. 18 [1983] 355/69, 365/7). [8] Rychagov, A V.; Korolev, Yu. M.; Bratishko, V. D.; Rakov, E. G. (Tr. Inst. Mosk. Khim. Tekhnot. Inst. No. 62 [1969] 52/6). [9] Caiola, A.; Guy, H.; Sohm, J. C. (Entropie No. 40 [1971]24/34; C.A. 76 [1972] No. 104736). [10] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [11] LaValle, D. E.; Steele, R. M.; Wilkinson, M. K.; Yakel, H. L., Jr. (J. Am. Chem. Soc. 82 [1960] 2433/4). [12] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald R. A.; Syverud, AN. (JANAF Thermochemical Tables, 3rd Ed., Pt. 11, Midland, Mich., 1985/86, p. 1121). [13] Emeleus, H. J.; Gutmann, V. (J. Chem. Soc. 1949 2979/82). [14] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970]116/21). [15] Vasil'ev, Va. V.; Khaldoyanidi, K. A.; Opalovskii, A. A.; Yudin, V. M. (Fiz. Tverd. Tela [Leningrad]13 [1971]1840/3; Soviet Phys.-Solid State 13 [1971]1543/5). [16] Hoppe, R.; Lehr, K. (Z. Anorg. Allgem. Chem. 416 [1975] 240/50). [17] Wilkinson, M. K.; Wollan, E. 0.; Child, H. R.; Cable, J. W. (Phys. Rev. [2]121 [1961]74/7). [18]. Wollan, E. 0.; Child, H. R.; Wilkinson, M. K.; Cable, J. W. (ORNL-2610 [1959]1/64, 34/5; N.S.A 13 [1959] No. 9108). [19] Wilkinson, M. K.; Wollan, E. 0.; Child, H. R.; Cable, J. W. (ORNL-2910 [1960]50/4; N.S.A. 14 [1960] No. 13060). [20] Wilkinson, M. K.; Wollan, E. 0.; Child, H. R. (Bult. Am. Phys. Soc. [2] 4 [1959] 242). [21] Smith, P. W.; Lewis, J.; Nyholm, R. S. (unpublished results, cited by [22]). [22] Fergusson, J. E. (Halogen Chem. 3 [1967] 227/302, 256). [23] Wollan, E. 0.; Koehler, W. C. (Phys. Rev. [2]100 [1955] 545/63, 560). [24] Weaver, C. F.; Friedman, H. A; Hess, D. N. (ORNL-4229 [1968] 33/7; N.SA 22 [1968] No. 25374). GmeLin Handbook Mo Suppl. Vol. B 5 6 82 MoLybdenum Fluorides [25] Fukutomi, M.; Corbett, J. D. (J. Less-Common Metals 55 [1977]125/30). [26] Rychagov, A. V.; KoroLev, Yu. M. (Zh. Neorgan. Khim. 23 [1978] 263/5; Russ. J. Inorg. Chem. 23 [1978] 149/50). 2.2.4.5 Chemical Reactions. Solubility Thermal Decomposition. Upon heating in Ni or Cu capsuLes at 500 and 710°C, respectiveLy, under its own pressure for periods in excess of 10 d, disproportionation was not observed [2]. In a dynamic vacuum, MoF3 is stabLe up to 500°C but begins to disproportionate into Mo and higher voLatiLe fluorides at 600°C [3]. The gas escaping at 500 to 700°C from a Knudsen ceLL Loaded with MoF3 is predominantLy MoFs with Lesser amounts of both MoFs and MoF4. The ratio of MoF4/MoFs increases with temperature [4]. Above 775°C, the thermaL decomposition of MoF3 is compLete, Leaving a residue of metallic moLybdenum. The composition of the vapor over MoF3 vs. temperature is shown in Fig.42 [5]. 1oo .....------, \ , \ .... - ..... 80 \ ," " \ l ~\ \ I ' \@/ ' " 0 '\ \ \e MoF4 .t I ~ ••• X I I ./ I \ o MoFv. I Cl. h, MO~ o I \ •• I > / \., / I Fig. 42. Percent composition of the vapor over 20 I I '....@ .... __@I' I / MoF3 (dashed Lines) and MoF4 (fuLL Lines) [5]. I @ ------I / @ MoF6 / ... °0~~~~L-~~~6~00~--8=070~ Knudsen cell temperature in 'e The disproportionation of MoF3 was studied by mass spectra (MS) recorded at 911, 930, and 964 K. With 72 eV eLectrons the saturated vapor over MoF3 at 964 K yieLds the foLLowing MS: species ...... Mo+ MoF+ MoF~ MoF~ MoFt MoF! Mo2F! Mo2Ft M02F~ a) i ntensity ...... 11.5 11.5 12.0 50 35 2.85 0.0076 0.0082 0.012 a) presumabLy Mo2F; By Knudsen effusion studies MoF4 was identifiedas the main gaseous decomposition product of MoF3• In addition, MoFs and sm aLL amounts of MoF3 , Mo2Fs, and Mo2FlO were found. The reLative composition of the vapor (in %) at different temperatures [6]: Tin K MoF3 MoF4 MoFs 911 0.4 94.8 4.8 930 0.5 92.1 7.4 964 1.1 91.1 7.8 G meli n Hand book Mo Suppl. Vol. B 5 83 The fineLy divided Mo formed by the disproportionation does not react with the solid MoF3 as deduced from the Long term constancy of the ion currents observed in the MS [6]. The foLLowing partiaL pressures p (in Torr) were determined from MS [7]: Tin K p(MoF5) 911 8.82 x10-5 0.0224 0.00114 964 1.77 x10-3 0.146 0.0124 1.13 X 10-5 7.71 xlO-s The temperature dependence of the partiaL pressures p (in Torr) is approximated between T=850 and 970 K by Log p=A-BfT as foLLows [7]: species A B MoF3 13.39±0.2 15700 ±330 MoF4 12.7±0.05 13050 ±110 MoF5 11.88 ± 0.1 13400±110 From the temperature dependence of the mass spectrometric data in the region 850 to 950 K the enthaLpies of the disproportionation reactions, ßH298, have been determined as foLLows [7,8]: reaction ßH298 in kcaVmoL 413 MoF3(s) -> 113 Mo(s) + MoF4(g) 62.9±0.9 513 MoF3(s) -> 213 Mo(s) + MoF5(g) 65.3±0.9 3 MoF3(s) -> Mo(s) + MoF4(g) + MoF5(g) 128.2± 1.3 A disproportionation temperature of 1373 ± 100 Kat atmospheric pressure was found to be reasonabLy consistent with the observations described in the above clted Literature [9]. The gas-phase reaction MoF2 + MoF4~2MoF3 was studied by MS in the SFs + Mo system at 1664 to 2146 K and in the MoFs+ Mo system at 2054 to 2230 K. The enthaLpies of reaction, ßH,.298derived forthe SFs+ Mo system are -14.8 and -14.1 kcaVmoL forsecond and third Law evaLuations, respectiveLy. The corresponding vaLues obtained with the MoFs + Mo system are -18.2 and -14.0 kcaVmol. The equiLibrium constant K of the MoF2 + MoF4~2MoF3 reaction depends on temperature as foLLows [19]: K (from SFs+ Mo system) 339,353,328 358 288 227 268 185 142 125 Tin K ...... 1664 1677 1740 1795 1806 1927 2046 2146 K (from MoFs+ Mo system) .... 151 147 128 125 106 T in·K ...... 2054 2100 2140 2178 2230 Reactions with Elements, Pure MoF3 is reLativeLy stabLe in air at room temperature [10]. In sampLes that had been exposed to air for severaL years, Mo02F2 was detected in the effusing vapor at 400°C [11, 12]. Upon heating in air [13] orin O2 (-0.8 atm) at 200°C. MoOF3forms [14]. Oxidation to Mo03 and formation of HF on heating in air has been stated in [1]. In a stream of hydrogen at atmospheric pressure MoF3 is stabLe at 300°C. In the temperature region 400 to 500°C (6 h) fLuorine removal is incompLete. The residue consists of Mo and MoF3. Above 500°C practicaLLy compLete reduction to metallic Mo was observed. Disproportionation with the formation of higher fluorides does not occur [15, 16]. A sLight Loss in weight at 440°C (2 h) and quantitative reduction to the metaL at 650°C (1 h) in pure hydrogen was stated in [1]. A Gmelin Handbook Mo Suppl. Vol. B 5 6' 84 MoLybdenum Fluorides thermodynamic study of the reduction of the hexafluoride by hydrogen (see p. 166) in the temperature region 298 to 1600 K shows that the reduction of MoF3 via MoF2 as an intermedi ate is impossibLe. Free energies and equiLibrium degrees of conversion for the reaction MoF3(S)+1.5H2(g)~Mo(s)+3HF(g) are plotted vs. temperature in [17). The reaction with bromine at 100 to 130°C (8 to 10 h) yieLds MoBr2F3 [18). For the reaction MoF3+ S ~ SF + MoF2 the gaseous reaction equ iLibria have been deter mined by mass spectrometric anaLysis of the effusing gas produced by reacting Mo with SFs in a Knudsen ceLL at 1664 to 2146 K. The equiLibrium constant K·lOs is 9.79 (average of three measurements) at 1664 K and 98.5 at 2146 K. The enthaLpy change ~H298 = 38.2 ± 1.5 and 38.4 kcaLlmoL was caLcuLated by appLying the second and third Law methods, respectiveLy [19, 20). Upon equiLibration with Mo in seaLed Mo tubes no significant reduction of MoF3 couLd be detected at temperatures up to 850°C (7 d). Though the equiLibration products change their coLor (see p. 80), no changes in the chemicaL composition and powder diffraction data occur [10). Pure MoF3 does not react with Ni or Cu when heated at 500 to 700°C in seaLed capsuLes made of these metals [21). Reactions with Compounds. In water vapor (18 Torr) with excLusion of air, formation of hydrates was not observed at room temperature [14). MoF3 is unaffected by 40 wt% hydrofLuoric acid, but is decomposed by hot concentrated acids and by coLd aqua regia [1). With coLd soLutions of sodium hydroxide there is a sLow reaction, but the compound dissoLves by boiLing with a mixture of aqueous NaOH and H20 2 [1). MoF3 is soLubLe in hot aLkali soLutions [22). MoF3 has been shown to react with LiF to form at Least two binary compounds [23). With stoichiometric quantities of the corresponding binary fluorides at 500 to 600°C (8 d), the compounds K2NaMoFs, Rb2NaMoFs, Rb2KMoFs, Cs2KMoFs, TL2NaMoFs, TL2KMoFs, and Cs2TLMoFs were obtained [24). In the LiF-BeF2-MoF3 system aLong the join Li2BeF4-MoF3 the compounds LiMoF4 and LisM02F11 have been identified [25), see aLso [26). In [27) the stoichio metry of the former compound was estabLished as Li2MoFs. In moLten Li2BeF4 soLution smaLL amounts of MoF3 (800 ppm MOIII, added in the form of Li3MoFs) appear to be stabLe at 500°C (23 h). At 700°C a marked decrease of the MOIII concentration in the fiLtered sampLe suggest that Mo metaL forms by disproportionation [25). When sampLes of composition MoF3+ LiF + BeF2 (10:60:30 moL%) were heated at 500 to 800°C in a Knudsen ceLL, gaseous MoF4 , MoFs, and MoFs were mass spectrometricaLLy detected in the vapor phase. The ratio MoF4/MoFs increases with temperature and MoF4 becomes the dominant species at about 590°C. At 600°C additionaL fragments were observed wh ich are probabLy LiF· BeF2· MoF~ and Li2Be2Mo+ [26, 28). The rate of MOIII removal from the melt was found to vary with the experimentaL conditions, especiaLLy with the mode of heating. Second-, first-, and haLf-order kinetics were stated [29). At 500°C with an He fLow rate of 12 Uh and with static He the haLf-order rate constant is 8.1 x 10-3 and 7.3 X 10-3 ppm1/2/h, respectiveLy [26). The rate of the process was not significantLy affected by the surface of the copper container or the quantity of Mo produced by the disproportionation [30). In the vapor phase generated by heating a mixture of MoF3 and KBe 2Fs (-0.5 moL%) in an effusion ceLL, the ions BeFä, Be2Fs, Be3Fi, KBe2FS, BeMoFi, MoFs, and MoFs were mass spectrometricaLLy detected. The occurrence of oxygen-containing species was caused by impurities of the MoF3 sampLe [31). The mass spectrometric study of the vapor phase over a mixture of MoF3 and Mo02F2 in a Knudsen ceLL at 751 K showed that the saturated vapor contained onLy MoOF3 and Mo02F2 moLecuLes. At 823 K when the Last portions of the GmeLin Handbook Mo Suppl. Vol. B 5 MoFa 85 components were in the gaseous state, appreciabLe amounts of MoFa, MoF4, and MoFs were found in addition to the oxide fluorides [32]. A soLution of the trifluoride in moLten Li 2BeF 4 reacts readiLy with Ni at 500°C yieLding Mo and NiF2. The reaction is Less marked with Cu. With UF3 in Li 2BeF4 at 500°C, MoF3 reacts via MoF3+3UF3~Mo+3UF4 [2]. The presence of 1 to 2 moL% of UF4 in the Li2BeF4+MoF3 sampLes has no appreciabLe effect on the thermaL decomposition of MoF3. The addition of UF3 (-5000 ppm UIII) to the system LiF-BeF2-MoF3-MoF4 reduces the MOIII at Least a thousand times faster than the disproportionation does. However, no effect was observed with 100 ppm UIII and MOIII in excess [26]. Solubility. MoF3 is onLy sLightLy soLubLe in water and insoLubLe in organic soLvents such as aLcohoL, CCL4, or CsHs [1]. References: [1] EmeLeus, H. J.; Gutmann, V. (J. Chem. Soc. 1949 2979/82). [2] Weaver, C. F.; Friedman, H. A. (ORNL-4191 [1967]143/4). [3] LaVaLLe, D. E.; SteeLe, R. M.; WiLkinson, M. K.; YakeL, H. L., Jr. (J. Am. Chem. Soc. 82 [1960] 2433/4). [4] StrehLow, R. A.; Redman, J. D. (ORNL-4254 [1968]134/6). [5] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970]116/21, 117). [6] ALikhanyan, A. S.; StebLevskii, A. V.; MaLkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978]1477/82; Russ. J. Inorg. Chem. 23 [1978] 814/7). [7] ALikhanyan, A. S.; Pervov, V. S.; MaLkerova, I. P.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978]1483/5; Russ. J. Inorg. Chem. 23 [1978] 817/8). [8] ALikhanyan, A. S.; StebLevskii, A. V.; MaLkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 29; C.A. 90 [1979] No. 29936). [9] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980]11/191, 58). [10] Fukutomi, M.; Corbett, J. D. (J. Less-Common Metals 55 [1977]125/30). [11] StrehLow, R. A.; Redman, J. D. (ORNL-4191 [1967]144/7). [12] Redman, J. D.; StrehLow, R. A. (ORNL-4229 [1968]37/9; N.S.A. 22 [1968] No. 25374). [13] Pervov, V. S.; Butskii, V. D.; Novotortsev, V. M. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 226; C.A. 89 [1978] No. 208231). [14] Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981] 573/6; Russ. J. Inorg. Chem. 26 [1981] 310/2). [15] KoroLev, Yu. M.; Rychagov, A. V. (Izv. Akad. Nauk SSSR MetaLLy 1978 No. 6, pp. 16/22; Russ. Met. 1978 No. 6, pp. 14/8). [16] Rychagov, A. V.; KoroLev, Yu. M. (Zh. Neorgan. Khim. 23 [1978] 263/5; Russ. J. Inorg. , Chem. 23 [1978] 149/50). [17] Kopchikhin, D. S.; Rychagov, A. V.; Korolev, Yu. M.; Rakov, E. G. (Tr. Inst. Mosk. Khim. TekhnoL. Inst. No. 62 [1969] 60/2; C.A. 75 [1971] No. 80810). [18] Khaldoyanidi, K. A.; OpaLovskii, A. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1973 142/5; C.A. 79 [1973] No. 12985). [19] HiLdenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [20] HiLdenbrand, D. L. (NucL. Instrum. Methods Phys. Res. 186 [1981] 357/63). [21] Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970] 113/5). [22] Johnson, R. L.; SiegeL, B. (J. Inorg. NucL. Chem. 31 [1969} 955/63). [23] Weaver, C. F.; Friedman, H. A. (ORNL-4191 [1967] 142/3). GmeLin Handbook Mo Suppl. Vol. B 5 86 Molybdenum Fluorides [24] Hoppe, R.; Lehr, K. (Z. Anorg. Allgern. Chem. 416 [1975] 240/50, 241). [25] Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4229 [1968] 33/7; N.S.A. 22 [1968] No. 25374; ORNL-4254 [1968]129/34). [26] Weaver, C. F.; Friedman, H. A.; Gooch, J. W.; Redman, J. D. (ORNL-4396 [1969]157/62; N.S.A. 23 [1969] No. 47170). [27] Brunton, G. (Mater. Res. Bult. 6 [1971] 555/60, 555). [28] Redman, J. D. (ORNL-4400 [1970] 36/9). [29] Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4344 [1968] 153/5; N.S.A. 23 [1969] No. 21451). [30] Weaver, C. F.; Friedman, H. A.; Grimm. F. A. (ORNL-4449 [1970]115/6). [31] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982] 145/56, 146). [32] Alikhanyan, A. S.; Steblevskii, A. V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978] 2549/52; Russ. J. Inorg. Chem. 23 [1978]1412/3). 2.2.5 Molybdenum(IV) Fluoride MoF4 Older data are given in "Molybdän", 1935, p. 150. Survey. Already in 1826 Berzelius tried to prepare MoF4 but without success. It was not until 1957 that MoF4 has been obtained unquestionably from Mo(CO)s and F2• Since then various methods of preparation have been developed. MoF4 has also been observed in the Mo-F system. The crystal structure of MoF4 is still unknown. The green compound is extremely hygroscopic. In organic solvents various addition compounds are formed, e.g., with organic amines. 2.2.5.1 Preparation. Formation The light-green solid compound was prepared forthe first time in 1957 by reacting Mo(CO)s with fluorine at -75°C and subsequent decomposition of the olive green reaction product (M02Fg ?) at 170°C in a vacuum. Volatile MoFs was removed and MoF4 remained as the residue [1]. The same method but with fluorination at - 65°C and vacuum treatment at 100°C was applied later [2]. When excess Mo(CO)s is fluorinated with IFs in the cold, only impure MoF4 (mixed with MoF3) is obtained as a reddish brown solid [3]. By direct interaction of Mo(CO)s and MoFs (in excess) a mixture of MoFs and MoF4 forms on reaction at room temperature and the former is separated by vacuum sublimation. Green MoF4 amounting to about the same weight as the pentafluoride remains in the bulb [4,5]. During the reduction of MoFs by metallic Mo in a reactor with Mo heating filaments at 0.5 to 0.6 atm, MoF4 forms at filament temperatures of 300 to 400°C and deposits on the walls cooled to 100 to 150°C. It is purified by thermal treatment at 200°C in a dynamic vacuum. The tetrafluoride can also be obtained in addition to solid MoF3 by the same method with CF4 as the original fluoride at 0.5 to 0.8 atm and Mo filament temperatures 1200 to 1500°C [6]. Attempts to produce MoF4 by the reduction of MoFs with hydrogen were unsuccessful [9]. However, the formation of the compound as an intermediate during this reduction was found to be thermodynamically possible [11]. The formation of gaseous MoF4 during the hydrogen reduction of MoFs at 800°C is probably caused by the reaction MoF3 + MoFs ~ MoF4 + MoFs [12,13]. Gmelin Handbook Mo Suppl. Vol. B 5 87 Pure MoFs (prepared by refluxing MoF6 over Mo metal, see. p. 94) was sLowLy heated to 200°C under refluxing conditions whiLe maintaining the pressure in the 10-3 Torr range. The MoFs disproportionates to pure soLid MoF4 and gaseous MoF6 which was removed by pumping [7]. MoF4 production by treating MoFs with metallic Mo at 200 to 210°C for 40 to 48 h in a vacuum and subsequent vacuum heat treatment of the resuLting product is proposed in [8]. MoFs (1.0 g) can be converted to MoF4 by reacting with Si powder (34 mg) frozen in 10 mL of anhydrous HF for 6 to 12 h. VoLatiLe products are removed by vacuum evaporation and MoF4 (0.9 9 = 97% yield based on Si) is isoLated as a paLe yelLow-green powder. The direct reaction of MoF6 with two equivaLents of Si stops with the formation of a green oil (Mo2Fg ?) which occludes the unreacted Si. The decomposition of the oiL at -100°C yields MoFs and only a smalL amount of MoF4 [9]. Green products containing 98% MoF4 were obtained by reacting MoFs with Si (mole ratio 4: 1) in an autoclave. Stoichiometric amounts of the finely ground starting materiaLs were intimateLy mixed under dry argon and slowly heated to 140°C for 2 d then at 220°C for 15 d. The valve of the autoclave was opened every two days to remove the gaseous SiF4 . The final product was degassed at 100°C in a vacuum. Depending upon the material of the autoclave used (stainLess molybdenum steel or Ni lined with Cu) two different preparations of MoF 4 have been obtained [16]. FLuorination of MoS2 by SF4 at moLe ratio 0.15:0.4 gives the corresponding fluoride MoF4. The reaction was carried out at 350°C (8 h) in apressure vesseL. The crude product was extracted with CS2 to remove the sulfur [10]. Gaseous MoF4 occurs as a product of disproportionation of MoF3, MoFs, and MoF6, see pp. 82, 112, and 164, respectiveLy, and by the gaseous reaction between MoF3 and MoFs, see p. 91. Gaseous MoF4 was aLso detected in the effusion vapor on heating MoF6 with Mo (see p. 169), MoF3 with Mo02F2 (see pp. 84/5), and SF6 with Mo [14,15]. References: [1] Peacock, R. D. (Proc. Chem. Soc. 195759). [2] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568/74,1569). [3] Hargreaves, G. B.; Peacock, R. D. (J. Chem. Soc. 19584390/3). [4] Hargreaves, G. B.; Peacock, R. D. (from [2]). [5] Edwards, A. J.; Peacock, R. D.; SmalL, R. W. H. (J. Chem. Soc. 1962 4486/91). [6] Pervov, V. S.; Butskii, V. D.; Podzolko, L. G. (Zh. Neorgan. Khim. 23 [1978]1486/91; Russ. J. Inorg. Chem. 23 [1978] 819/22). [7] Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970] 113/5). [8] OpaLovskii, A. A.; Fedorov, V. E.; Khaldoyanidi, K. A. (U.S.S.R. 265879 [1968/72]; C.A. 78 [1973] No. 6040). [9] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974] 1529/31). [10] Oppegard, A. L.; Smith, W. C.; Muetterties, E. L.; Engelhardt, V. A. (J. Am. Chem. Soc. 82 [1960] 3835/8). [11] Kopchikhin, D. S.; Rychagov, A. V.; Korolev, Yu. M.; Rakov, E. G. (Tr. Inst. Mosk. Khim. TekhnoL. Inst. No. 62 [1969] 60/2; C.A. 75 [1971] No. 80810). [12] Rychagov, A. V.; KoroLev, Yu. M.; Pobedash, N. V. (Sb. Metall. MetalLoved. Chist. Met. M 1975 No. 11, pp. 37/47, 39; C.A. 85 [1978] No. 48830). [13] KoroLev, Yu. M.; Rychagov, A. V. (Izv. Akad. Nauk SSSR Metally 1978 No. 6, pp. 16/22; Russ. Met. 1978 No. 6, pp. 14/8). [14] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [15] Hildenbrand, D. L. (NucL. Instrum. Methods Phys. Res. 186 [1981] 357/63). [16] Couturier, J.-C.; Angenault, J.; Mary, Y.; Quarton, M. (J. Less-Common Metals 138 [1988] 71/7,72). Gmelin Handbook Mo Suppl. Vol. B 5 88 Molybdenum Fluorides 2.2.5.2 The Moleeule For the molecule the point group Td is usually assumed [1 to 7], D4h was considered in addition in [6]. The bond length r(Mo-F) was assumed as 1.82 [7], 1.83 [1,2,5]. or 1.84 A [3, 4]. The resulting moment of inertia of the spherical top (Td symmetry) is (in 10-40 g. cm2) 283 [1, 2, 5] or 285 [3]. The following fundamental frequencies (in cm-1) and degeneracies have been assumed for the molecule: Vl V2 V3 V4 Ref. 624 (1 x) 155 (2x) 674 (3x) 190 (3x) [1] 624 (1 x) 155 (2x) 674 (3x) 190 (4x?) [5] 624 155 674 198 [2] 700 (1 x) 160 (2x) 750 (3x) 180 (3x) [3] The ground state statistical weight 1 (singlet) is assumed in [3]. On the other hand, the following energy levels (degeneracies in parentheses) have been assumed in calculations of thermodynamic properties: 0 cm-1 (3x), 15000 cm-1 (11 x), and 20000 cm-1 (9x). The total multiplicity was said to be 21 [7]. Using the method given in [8] the effective charge q on the Mo atom has been calculated. For r(Mo-F) = 1.84 Aand D4h symmetry, q = 0.68 e. For r = 1.83 A. q = 0.73 and 0.69 e for D4h and Td symmetry, respectively [6]. For gaseous MoF4 the heat of dissociation has been estimated at 503 kcaVmol on the basis of a review of thermochemical literature data [10]. The bond dissociation energy D298(F3Mo-F) = 105 kcaVmol was evaluated from ~Hf.298[MoF4(g)] = - 228.0 ± 3.9 kcaVmol derived from gas phase equilibria [3,11]. The bond energy 130.1 kcaVmol was calculated in [12] citing from Russian handbooks the ~Hf.298[MoF4(S)] value of -287 kcaVmol. At an electron impact energy of 72 eV, the mass spectrum of MoF4 molecules shows the following ions (AP = appearance potential) [9]: ion ...... Mo+ MoF+ MoFt MoF~ MoF~ intensity ...... 59 52 51 175 100 AP in eV ...... 19.0 ± 1.0 14.01 ±0.5 9.74±0.2 References: [1] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 4, pp. 12/22,18; C.A. 69 [1968] No. 110616). [2] Galkin, N. P.; Tumanov, YU. N.; Butylkin, YU. P. (Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [3] Hildenbrand, D. L. (J. Chem. Phys. 65 [1975] 614/8). [4] Spiridonov, V. P.; Romanov, G. V. (Vestn. Mosk. Univ. Sero 11 Khim. 24 No. 1 [1969]65/8; Moscow Univ. Chem. Bull. 24 No. 1 [1969] 51/3). [5] Tumanov, YU. N.; Galkin, N. P. (Zh. Fiz. Khim. 43 [1969] 836/40; Russ. J. Phys. Chem. 43 [1969] 464/6). [6] Pervov, V. S.; Fal'kengof, A. T.; Murav'ev, E. N. (Koord. Khim. 5 [1979] 155/8; Soviet J. Coord. Chem. 5 [1979] 117/20). [i] Brewer, L. (Proc. Electrochem. Soc. 78-1 [1978] 177/86). [8] J0rgensen, C. K.; Horner, S. M.; Hatfield, W. E.; Tyree, S. Y. (Intern. J. Quantum Chem.1 [1967] 191/215). Gmelin Handbook Mo Suppl. Vol. B 5 89 [9] ALikhanyan, A. S.; StebLevskii, A. V.; MaLkerova, I. P.; Pervov, V. S.; Butskii, V.D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978]1477/82; Russ. J. Inorg. Chem. 23 [1978] 814/7). [10] Feber, R. C. (LA-3164 [1964]1/187, 178; C. A. 63 [1965] 9124). [11] HiLdenbrand, D. L. (NucL. Instrum. Methods Phys. Res. 186 [1981] 357/63). [12] Drobot, D. V.; Pisarev, E. A. (Zh. Neorgan. Khim. 26 [1981]3/16; Russ. J. Inorg. Chem. 26 [1981] 1/8). 2.2.5.3 Crystallographic Properties The crystaL structure of MoF4 has not been reported. The d vaLues were given tor sampLes prepared by reducing MoFs with Si [1, 2]. Depending upon preparation conditions d vaLue tabLes ot presumabLy two products showing different X-ray powder diagrams have been given. The compositions of both products are beLieved to be very eLose to that ot MoF4 [2]. References: [1] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [2] Couturier, J.-C.; AngenauLt, J.; Mary, Y.; Quarton, M. (J. Less-Common Metals 138 [1988] 71/7, 72). 2.2.5.4 Physical Properties Thermodynamic Data. The standard entropy tor soLid MoF4, S~alR = 14 ± 2 corresponding to S~[MoF4(S)] = 27.8 cal' mol-l, K-1 was estimated by [2]. The much larger estimate 42±5 cal·moL-1·K-1 is given in [5]. For an S298 estimate tor the Liquid, see [6]. For gaseous MoF4, S~[MoF4(g)] = 78.59 ±2 [1,2],78.63 [3}, and 76.28 caL· moL-1. K-1 [4]. ST is tabulated for gaseous MoF4 in [1, 3, 4]. It ranges from 250.8 to 466.0 J. moL-1. K-1 tor T = 100 to 1200 K [3], trom 82.70 to 146.14 cal· moL-1. K-1 tor T= 400 to 5000 K [4], and from 89.91 to 134.85 cal· mol-1. K-1 for T = 500 to 3000 K [1]. For vaLues between 0 and 6000 K see [7]. For solid MoF4' <;fR = 12.5 + 0.0005 T was estimated in [2]. The heat capacity of gaseous MoF4 is approximated between 298 and 3000 K by <;fR = 12.76 - 226600IT2 + 4.5 X 10-8 T2 ± 0.3 [1, 2}. For the heat content of gaseous MoF4 at 298 K, (H~- Hü)/R = 2274 ± 100 K is given in [1]; aLso see [2]. F.or solid MoF4 between 298 and 600 K, - (Go- H~)/RT = 12.5 ln T + 3750IT - 69.87 + 0.00025 T ± 2 is given in [2]. The estimated - (G-H298)IT for gaseous MoF4 is 76.5 caL' mol-1. K-1 at 298 K and ranges from 77.3 to 105.1 caL· moL-1. K-1 tor T between 400 and 2400 K [8]. ALso for the gas, - (Go -H298)/RT is approximated between 298 and 3000 K by 12.762 LnT -113500IT2 +4570IT - 47.22 - 0.00001 T± 1 [1], also see [2]. The caLcuLated + (Go- H~)IT decreases from 397.2 to 390.4 J·mol-1·K-1 when T increases from 100 to 1200 K [3]. For gaseous MoF4, - (Go - Hü)IT is tabulated and ranges from 65.84 to 121.37 caL· mol-1. K-1 as T ranges from 400 to 5000 K [4]. VaLues tor~, (Go - H~8)IT, and W - H298 between 0 and 6000 K are Listed in [7]. For estimated sublimation and vaporization enthaLpies and entropies, see the paper [6] wh ich also gives estimated ßH298, S298' and Cp. 298 vaLues tor the Liquid [6]. Gmelin Handbook Mo Suppl. Vol. B 5 90 Molybdenum Fluorides Thermodynamic Data of Formation. For solid MoF4, L1Hf'. 29s[MoF4(s)] was estimated by [2] considering in part disproportionation studies on MoF4 (ORNL reports by Weaver et al.), but mainly considering the disproportionation of MoF5 (studied by [10]); L1Hf'. 298[MoF4(s)]/ R = -139000 ± 2000 K corresponding to L1Hi. 298[MoF4(s)] = - 276.2±4 kcaVmol [2]. The value L1Hf'. 298[MoF4(s)] = - 287 kcaVmol is given in [4, 11] ([11] citing various handbooks; [4] citing a book by Veryatin, U. D. et al. published in 1965). Using semi-empirical methods, the value L1Hf'.29S[MoF4(s)] = - 300 ± 15 kcaVmol was estimated by [5]. From gas phase equilibria L1Hf'.29S[MoF4(g)]=-228.0±3.9 kcaVmol [8,9]. An error of only ±1.9 kcaVmol was stated by [2]. The value L1Hi. 298[MoF4(g)]/R= -114000 ± 2000 K [1] (±5000 K[2]) corresponding to - 226.5 kcaVmol has been estimated in the reviews [1,2]. L1Hf'values between 0 and 6000 K are listed in [7]. For the free energy of formation at T = 298 K, L1Gf'. 29s/RT = - 428 ± 4 and - 370 ± 16 have been estimated for solid and gaseous MoF4, respectively [2]. L1Gf'values between 0 and 6000 K are listed in [7]. Magnetic Properties. The magnetic susceptibility X of MoF4 was studied by the Faraday method between 77 and 298 Kin [12] and between ~ 80 and ~ 285 Kin [13]. The Xmol vs. T cu rve plotted in [13] decreases from (X in 10-3 cm3/mol) ~ 1.6 near 85 K to -1.1 near 285 K [13]. Due to antiferromagnetic coupling of the magnetic moments, the measured !leff at room tempera ture is below the spin-only value (and even more reduced at the lower temperatures). The measured !leff vs. T curve is in favor of a "polymerie" rather than a "dimeric" interaction model for the antiferromagnetic coupling [12]. Optical Properties. Color. Solid MoF4 is yellowish tan [14], yellow-green [15], light green [16], or green [17]; (the sample of [14] was furnished by [18]). IR and Raman Spectra. MoF6 matrix isolated at 6 ± 1 K (MoF6 :Ar= 1 :500) was studied by IR. A feature at 674 cm-1 observed after photolysis by UV irradiation was attributed to MoF4 [19]. With an IR study of matrix isolated MoF5 (Ar matrix at 20 K), a feature observed at 733 cm-1 was attributed to MoF4 [20]. In the range 100 to 900 cm-1, solid MoF4 shows the following Raman shifts (in cm-1): 142(w), 176(w), 211(m), 251(m), 280(w), 690(w), 710(w), 722(s), and 746(m) [14]. IR frequencies (in cm-1) observed with a powdered sample: 554(m, br), 721 (s, sh), 723(s), 738(m, sh) [15]. The 690, 710, 722, and 746 cm-1 shifts are attributed to Mo-F stretching modes. The 722 cm-1 vibration is likely to be the symmetrie stretching mode [14]. References: [1] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980] 11/191, 49). [2] Brewer, L. (Proe. Electrochem. Soc. 78-1 [1978] 177/86). [3] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982] 145/56). [4] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [5] Rychagov, A. V.; Korolev, Yu. M.; Bratishko, V. D.; Rakov, E. G. (Tr. Inst. Mosk. Khim. Tekhnol. Inst. No. 62 [1969] 52/6). [6] Dittmer, G.; Niemann, U. (Mater. Res. Bull. 18 [1983] 355/69). [7] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. (JANAF Thermochemical Tables, 3rd Ed. Pt. 11 [1985] 1137). [8] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [9] Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63). [10] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977]1149/63). Gmelin Handbook Mo Suppl. Vol. B 5 91 [11] Drobot, D. V.; Pisarev, E. A. (Zh. Neorgan. Khim. 26 [1981]3/16; Russ. J. Inorg. Chem. 26 [1981]1/8). [12] ELLert, O. G.; Butskii, V. D.; Novotortsev, V. M.; Pervov, V. S.; Volkov, V. V.; Kalinnikov, V. T. (Koord. Khim. 8 [1982] 39/43; C.A. 96 [1982] No. 95389). [13] Khaldoyanidi, K. A.; Yakovlev, I. 1.; Ikorskii, V. V. (Zh. Neorgan. Khim. 26 [1981]3067/9; Russ. J.lnorg. Chem. 26 [1981]1639/40). [14] Bates, J. B. (Inorg. Nucl. Chem. Letters 7 [1971] 957/60). [15] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [16] Peacock, R. D. (Proc. Chem. Soc. 1957 59). [17] Edwards, A. J.; Peacock, R. D.; SmaLL, R. W. H. (J. Chem. Soc. 19624486/91). [18] Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970]113/5). [19] Blinova, O. V.; Predtechenskii, Yu. B. (Opt. Spektroskopiya 47 [1979] 1120/5; Opt. Spectrosc. [USSR] 47 [1979] 622/4). [20] Acquista, N.; Abramowitz, S. (J. Chem. Phys. 58 [1973] 5484/8). 2.2.5.5 Chemical Reactions. Solubility MoF4 is extremely hygroscopic [1, 2]; see below. The behavior on heating is very sensitive to experimental conditions, especiaLLy refluxing and overpressure [3]. In a Knudsen ceLL (Cu) at temperatures below - 220°C, MoF4 neither evaporates nor decomposes. At higher temperatures, MoF4, MoFs, and MoF6 occur in the gas phase. The decomposition is complete at 750°C, the solid residue is metallic Mo [4]. Under nonrefluxing conditions, simultaneous evaporation und disproportionation was observed in the temperature range 500 to 700°C, while at lower temperatures (265 and 352°C) evaporation predominates. However, with refluxing conditions and an MoF6 overpressure of a few Torr, disproportionation predominates, wh ich at 250°C and pressure in the 10-3 Torr region proceeds via 2 MoF4(s) ~MoF3(S) + MoFs(g) and 3 MoF4(s) ~2MoF3(S) + MoF6(g) [3]. The dis proportionation temperature at atmospheric pressure is assumed to be 573 ± 40 K [6], see also [20]. The partial pressures of MoF6, MoFs, Mo2FlO, and MoF4 determined by mass spectrometry (MS) are plotted vs. T (see Fig. 42, p. 82) wh ich describes the complete sublimation of MoF4 in a Cu Knudsen ceLL (heating rate not given). Below 300°C, the presumable MoF4 melting point, the MoF4 seems to decompose according to 2MoF4(S)~MoF3(S)+ MoFs(g) and 3MoF4(s) ~ 2 MoF3(s) + MoF6(g). Above 550°C, the foLLowing processes are assu med to proceed simulta neously: MoF 4(l)~ MoF4(g), 3 MoF 4(l)~ 2 MoF3+ MoF6(g), 2 MoF3~ Mo + MoF6(g), and 2 MoFs(g) ~ MoF4(g) + MoF6(g) [5]. "fhe disproportionation in the gas phase, MoF3(g)+MoFs(g)~2MoF4(g) has been studied by MS at 1143 to 1608 Kin [8] and at 911 to 964 K in [22]. The change in free energy and the equilibrium constant have been measured and compared [22] with values calculated from data of [8] as foLLows: Tin K Kexp [22] Kreeale -~GT.exp - ~GT. reeale in kcaLJmol [22] in kcaLJmol 911 4681 4786 15.3 15.3 930 2293 3800 14.3 15.2 964 917 2754 13.1 15.2 Gmelin Handbook Mo Suppt. Vot. B 5 92 Molybdenum Fluorides The enthalpies of reaction ÖH 298 = -17.8 [2) (±0.6 [9)) and -17.2 kcaUmol [8,9) have been derived by second and third law evaluations, respectively (öH"= T [öSe - RinK) or -R [dinK! d(r1)), respectively), from equilibrium constants measured as follows [8): K ...... 600 674 419 196 123 105 88.9 62.1,68.7 Tin K ...... 1143 1146 1231 1377 1476 1523 1525 1608 The enthalpy for MoF4(g) + F-(g)-> MoF;(g), ÖH~8(F4Mo-F-) = - 382.0 ± 20.1 kJ/mol, has been determined from equilibrium data of the gas-phase reactions between MoF4 and BeF; or Be2F; (see below) and the known enthalpy of loss of F- for BeF; [7). For the reaction MoF4(g) + S(g)->SF(g) + MoF3(g) the equilibrium constant K·102 = 3.33 and 12.3 at 1664 and 2146 K, respectively, has been obtained by mass spectrometric analysis of the effusing gas produced by reacting Mo with SFe. The reaction enthalpy ÖH'.298 = 23.4 and 24.3 kcaUmol was calculated applying the second and third law methods, respectively [8, 9). MoF4 is reduced to MoF3 by metallic Mo at 400 to 410°C in a vacuum [10). In water, MoF4 is immediately hydrolyzed to form a colored solution [11). With water vapor at room temperature at p(HP) = 18 Torr, an increase in mass indicates the formation of hydrates MoF4·nH20 (n=4.0 to 7.5). Subsequent evacuation to 10-3 Torr leads to hydrolysis with formation of MoOF2 ·H20, see p. 190 [12). By fusion of MoF4 with KHF 2 at 250°C no pure phase could be isolated [13). Equilibria were measured in the vapor generated by reacting MoF3 with KBe 2F2 in an effusion cell with mass spectrometric recording of the ions. From the equilibrium constants (see the paper) for MoF4+2BeF;->MoF;+Be2F; at 840 to 921 K, an average ÖH~298=10.88±5.94 kJ/mol was calculated for MoF 4+ BeF; -> MoF; + BeF2. For MoF 4+ BeF; -> MoBeF"7 at T = 830 to 900 K, öH~ T = -170.7 ± 14.6 kJ/mol [7). Solid state reactions between MoF 4 and LnF3 yield ternary fluorides of composition LnMoF7 for yttrium and all lanthanides, Ln, except dysprosium [18,19). Equimolar amounts of MoF4 and MoOF4 react at about 200°C (8 to 10 h) to give MoFs and MoOF3 [14,15). The enthalpy of the reaction MoFig) + Mo02F2(g) ->2 MoOF3(g) at 823 K was determined as -3.6±2.5 kcaUmol and recalculated to ÖH~298= -4.1 ±3.0 kcaUmol with the assumption that C~[MoOF3(g)] = C~[MoF4(g)] [16). MoF4 is insoluble in anhydrous HF [1). It is soluble in ethers, such as tetrahydro furan or dimethoxyethane. Such solutions were used and organic donor compounds (pure or in ether sOlution) in excess were added to obtain the following addition compounds: MoF 4.2 N(CH3h. MoF4.2 (CsHsN) (both formulas are misprinted in table 1 of the paper [21)), MoF4·CeHsN(CH3b, MoF4·2(CH3bNCHO, and MoF4·2(CH3bSO [17,21). On reaction of MoF4 with CH3COCH 2COCH3 a very air-sensitive yellow solid was obtained [21). References: [1) Paine, R. T.; Asprey, L B. (Inorg. Chem. 13 [1974)1529/31). [2) Pervov, V. S.; Butskii, V. D.; Podzolko, L G. (Zh. Neorgan. Khim. 23 [1978)1486/91; Russ. J. Inorg. Chem. 23 [1978) 819/22). [3) Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970) 113/5). [4) Weaver, C. F.; Friedman, H. A.; Gooch, J. W.; Redman, J. D. (ORNL-4396 [1969]157/62; N.S.A. 23 [1969) No. 47170). (5) Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970)116/21). [6) Brewer, L (Proc. Electrochem. Soc. 78-1 [1978]177/86, 182). [7] Sidorov, LN.; Borshchevsky [Borshchevskii), A. Ya.; Rudny [Rudnyi), E. B.; Butsky [Butskii), V. D. (Chem. Phys. 71 [1982]145/56, 148/50). [8) Hildenbrand, D. L (J. Chem. Phys. 65 [1976) 614/8). Gmelin Handbook Mo Suppl. Vol. B 5 93 [9] Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63). [10] Opalovskii, A A; Fedorov, V. E.; Khaldoyanidi, K. A (U.S.S.R. 263581 [1968/72]; C.A 78 [1973] No. 6039). [11] Peacock, R. D. (Proe. Chem. Soc. 195759). [12] Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981]573/6; Russ. J.lnorg. Chem. 26 [1981] 310/2). [13] Edwards, A. J.; Peacock, R. D. (Chem. Ind. [London] 1960 1441/2). [14] Nikolaev, A. V.; Opalovsky [Opalovskii], A. A; Fedorov, V. E. (Therm. Anal. Proc. 2nd Intern. Conf., Worcester, Mass., 1968 [1969], Vol. 2, pp. 793/810, 800; C.A. 73 [1970] No. 94206). [15] Opalovskii, A. A; Anufrienko, V. F.; Khaldoyanidi, K. A. (Dokl. Akad. Nauk SSSR 184 [1969] 860/2; Dokl. Chem. Proc. Acad. Sei. USSR 184/189 [1969] 97/9). [16] Alikhanyan, A S.; Steblevskii, A V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978] 2549/52; Russ. J. Inorg. Chem. 23 [1978]1412/3). [17] Oppegard, A. L.; Smith, W. C.; Muetterties, E. L.; Engelhardt, V. A. (J. Am. Chem. Soc. 82 [1960] 3835/8). [18] Angenault, J.; Couturier, J. C.; Mary, Y.; Quarton, M. (J. Appl. Cryst. 20 [1987]133). [19] Couturier, J.-C.; Angenault, J.; Mary, Y.; Quarton, M. (J. Less-Common Metals 138 [1988] 71/7, 72). [20] Pervov, V. S.; Butskii, V. D. (Zh. Neorgan. Khim. 29 [1984]570/81 ; Russ. J. Inorg. Chem. 29 [1984]329/37,331). [21] Muetterties, E. L. (J. Am. Chem. Soc. 82 [1960] 108217). [22] Alikhanyan, A S.; Steblevskii, A. V.; Malkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgo raki, V.1. (Zh. Neorgan. Khim. 23 [1978]1477/82; Russ. J.lnorg. Chem. 23 [1978]814/7). 2.2.6 "Mo2Fg" There is no evidence for the existence of an individual M0 2Fg compound. An olive green solid of this composition was obtained in the fluorination of MO(CO)6 at -75 [1] or at -65°C [2]. The substance disproportionates at 100 [2] or at 170°C in a vacuum yielding volatile MoFs and solid MoF4 . X-ray data suggest that the green product is a mixture at room temperature and not a specific compound [1]. A green oil of similar composition and thermal behavior is obtained by reacting MoF6 with two equivalents of silicon in anhydrous HF. The substance is assumed to be a polymerized mixture of MoF4 and MoFs [3]. Studies of the MoF4-MoFs system by thermal analysis, X-ray diffraction, and magnetic susceptibility measurements confirm that there are no new compounds in this composition range (see p. 67). The magnetic susceptibilities found are almost additive [4]. References: [1] Peacock, R. D. (Proe. Chem. Soc. 195759). [2] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568174,1569). [3] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [4] Khaldoyanidi, K. A.; Yakovlev, I. I.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981] 3067/9; Russ. J. Inorg. Chem. 26 [1981]1639/40). Gmelin Handbook t.1o Suppl. Val. B 5 94 Molybdenum Fluorides 2.2.7 Molybdenum(V) Fluoride MoFs Survey. MoFs was first isolated in 1957 [1) from the reaction of Mo(CO)s with fluorine. Later methods are based on the reduction of molybdenum hexafluoride. Special care is necessary to minimize impurities and their effects. Particularly MoOF4 (see p. 194), wh ich is the main contaminant, is difficult to remove by thermal distillation since the vapor pressures of MoFs and MoOF4 are similar. MoFs and MoOF4 form solid solutions and even very small amounts of the oxide fluoride affects the properties of the pentafluoride, e. g., the melting point [2). Pure MoFs is a yellow crystalline substance at room temperature. It is very hygroscopic and must be handled either in a vacuum line or in an anhydrous, oxygen-free atmosphere. However, it appears quite stable in a dry stainless steel vessel and can be handled for short periods in a dry-box (P20 S) [3). MoFs also reacts with oxygen containing materials such as glass and presents a tendency to disproportionation wh ich can be statisfactorily suppressed only by a considerable partial pressure of gaseous MoFs [4). A characteristic feature of the compound is a tendency to undergo polymerization. Cyclic tetramers or polymeric chains are the structural units in the solid state. Mass spectrometric studies attest to association also in the vapor state. References: [1) Peacock, R. D. (Proc. Chem. Soc. 1957 59). [2) Khaldoyanidi, K. A.; Yakovlev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981) 3067/9; Russ. J. Inorg. Chem. 26 [1981)1639/40). [3) Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A.; Steven, A. M. (Inorg. Syn.13 [1972)146/50). [4) Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977)1149/63, 1156). 2.2.7.1 Preparation. Formation MoF5 occurs as a solid phase in the Mo-F system, see p.67. The direct fluorination by passing fluorine diluted with oxygen-free nitrogen over molybde num powder at 400°C in an Ni vessel yields MoF5 which is contaminated with a large proportion of MoOF4 . In a special trap arrangement MoOF4 can be separated from the pentafluoride by trap-to-trap sublimation at 65°C in vacuum [5). MoF5 is preferably prepared by the reduction of the hexafluoride. However, the synthesis of a pure product is complicated by the high sensitivity of both the MoFs and the MoF5 to moisture. Hydrogen fluoride, which forms as a product of hydrolysis and also occurs as an impurity in MoFs, is known to catalyze the reaction 2MoFs+3SiOr~3SiF4+2Mo03 (see p. 172) in glass vessels. Failure to remove HF resulted in several explosive ruptures of the Pyrex equipment [1,2). In addition, oxygen containing impurities lead to the formation of MoOF4 which is difficult to remove. Thus, elaborate efforts should be made to free the containing system and the reactants from contaminating impurities. Usually the meticulously cleaned apparatus (stainless steel, moneI, Teflon, Pyrex) was flamed under vacuum [1 to 4) and then pretreated with liquid MoFs [3,4). The MoFs was freed from HF by distillation over anhydrous NaF, see p. 119. With molybdenum as reducing agent the MoF5 was first prepared by passing the purified MoFs over molybdenum powder in an Ni tube at 300 to 400°C. The MoF5 was allowed to run from the tilted reaction vessel into a horizontal Pyrex receiver and was separated from the more volatile hexafluoride by trap-to-trap distillation [5). In a closed system powdered Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 95 moLybdenum reacts with gaseous MoF6 at -1 atm pressure in a previousLy evacuated moneL tube at 200°C, the MoFs condensing in an adjacent tube at room temperature. Subsequently, it is vacuum distiLLed at 70 to 80°C in the presence of the saturated vapor of MoF6 at dry-ice temperature (which serves to suppress spontaneous disproportionation of the pentafluoride). Standing at room temperature for a few hours is necessary for crystaLLization. When speciaL care was taken to avoid contamination during the process (for detaiLs see the paper) and very pure reactants were used, the impurity conte nt of the product was caLcuLated to be - 0.15 moL% [3,4). Reduction of the MoF6 at 150°C and purification of the MoFs by trap-to-trap distiLLation at 90°C in the presence of MoF6 (partiaL pressure -17 Pa) is described in (6). In a high-vacuum system (stainLess steeL vesseL, moneL cone) MoF6 (0.17 moL) is condensed onto powdered Mo metaL (0.0313 moL) cooLed to -196°C. Then the mixture is heated at 60°C for 24 h. The first portion of the MoFs wh ich contains as impurities the excess MoF6 and smaLL amounts of MoOF4 is purified in a speciaL apparatus (see the figure in the paper) which aLLows the removal of MoF6 by distiLLation at 90 to 100°C in a first step and the removal of MoOF4 by vacuum sublimation at 65°C in a second step. The main part of the MoFs preparation which is very pure couLd be stored in the reaction vesseL without further purification [7, 8). Pure MoF6 is refLuxed with a predetermined quantity of moLybdenum powder in a Pyrex container at temperatures in the range 25 to 75°C to prepare a soLution of MoFs in the MoF6. The excess MoF6 is pumped off at 75°C at pressures in the 10-3 Torr region and Leaving pure Liquid MoFs [9, 10). Further heating (up to 100°C) causes subLimation of the MoFs to the cooLer neck of the reaction vesseL (1). A process wh ich enabLes the production of MoFs with nearLy 100% yieLd and 99 to 99.9% purity invoLves the reduction of MoF6 by Mo at 120°C (20 h) in dry nitrogen in a copper autocLave, washing of the solid reaction product with anhydrous HF, and removal of the HF by vacuum evaporation (11). The reduction of gaseous MoF6 (-10-3 atm) at a moLybdenum fiLament produces MoFs at fiLament temperatures between 200 to 250°C. The product is condensed at - 78°C and purified by vacuum distiLLation (12). In areaction vesseL with an internaL cooLing by means of a screen, the optimum conditions for MoFs synthesis are: MoF6 pressures 10-2 to 10-3 atm, Mo fiLament temperatures 150 to 200°C, cooLing temperatures -70 to 20°C. The purity of the product increases with decrease of the initiaL MoF6 pressure and with decrease of the screen tempera ture (13). The reduction of MoF6 can also be carried out with an Mo (or W) wire coil heated resistiveLy to a duLL red glow using a very simple apparatus. The MoFs separates at the cooled walls of the Pyrex apparatus as a greenish yeLLow powder. At - 40 to - 50°C coolant bath temperature the reduction is quantitative after 5 to 6 h. Using hot tungsten wire and MoF6 at saturation vapor pressure with coolant bath temperatures of - 50 to - 40°C a fairly good yield of MoFs can be obtained after 4 h. Tungsten is absent from the MoFs formed (14). The reduction of MoF6 by H2 in anhydrous HF at room temperature in the presence of UV light (16) yields MoFs in 2 to 3 d. On the other hand, with a slurry of Si in HF as the reducing agent the reduction to MoFs proceeds at room temperature rapidly in 1 to 2 h. In both cases the volatile products are removed by vacuum evaporation leaving MoFs in high purity [15, 16). For further information on the reduction with Si see (35). The reaction of MoF6 with PF3 (see p. 171) was also found to provide a satisfactory method for preparing MoFs (17). Reduction of MoF6 with MO{CO)6 or W{CO)6 Leads to a mixture of MoFs and MoF4- The reaction is carried out at 25°C with MoF6 in excess. When the carbonyl is consumed, the remaining MoF6 is pumped off and the MoFs is separated by vacuum distillation at 100°C (5), see also (18). The yield and purity of the MoFs increases when MoF6 is treated at O°C with MO{CO)6 in Liquid HF in an atmosphere of dry N2• The solid product is washed with Liquid HF (19). GmeLin Handbook Mo Suppl. Vol. B 5 96 Molybdenum Fluorides MO(CO)6 treated with F2 at -75°C gives green M02Fg (see p. 93), which is then thermaUy decomposed to MoFs and MoF4• At 170°C in vacuum the yeUow MoFs volatilizes [20]. The MO(CO)6 can also be fluorinated at - 65°C and the MoFs is separated by vacuum treatment at 100°C [18]. The competitive reaction between NaMoF6 and SbFs which yields MoFs and NaSbF6 can be carried out at low temperatures where disproportionation and side reactions do not readily take place. For preparation of the pentafluoride a stoichiometric quantity of SbFs is distiUed onto a frozen solution of NaMoF6 in HF. Upon warming, NaSbF6 forms as a white precipitate. From the decanted solution HF is distiUed off, leaving a yeUow residue of MoFs which is further purified by sublimation at 85°C [21]. MoF4 and MoOF4 react at about 200°C for 8 to 10 h to produce MoFs and MoOF3. The MoFs condenses as a yeUow sublimate in the cold part of the ampule. Contamination of the pentafluoride with MoOF4 is suppressed when MoF4 is in excess [22]. Attempts to prepare MoFs from the corresponding chloride, MoCls, by stirring with HF were unsuccessful even at 100°C for extended periods [23]. Formation of MoFs was found to be the first step of the photodissociation of MoF6 in an argon matrix [24]. During the reduction of MoF6 by H2 at about 800°C, MoFs is probably formed by a side reaction between MoF6 and MoF3 [25,26]. When molybdenum is reacted with chlorine + hydrogen fluoride mixtures at 200 to 350°C, MoFs forms together with molybden um(V) chloride fluorides and a trace of MoF6 [33]. MoFs was also found in the products of the reactions between MoF6 and CS2 or WF4 at room temperature [27], between MO(CO)6 and liquid ReF6 [28], and between NF3, CF4 , or WF6 and Mo incandescent filaments [13]. SF4 may convert MoS2 to the pentafluoride as an intermediate step [29]. The thermal decomposition of MoBr2F3 in vacuum at 140 to 150°C yields MoFs in addition to MoBr3 and Br2 [30]. MoFs is obtained as a yeUow-orange solution in liquid S02 after filtration from the solid complex salts according to the equations KMoF6 + EIFx~ MoFs + KEIFx+ 1 where EI is B (x= 3) and As, Ta, or Nb (x = 5) [34]. Gaseous MoFs occurs as a product of thermal decomposition of MoF3 and MoF4 , see pp. 82, and 91, respectively, and in the effusion vapor generated by reacting MoF3 with Mo02F2, see pp. 84/5, or SF6 with Mo [31,32]. References: [1] Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4229 [1968] 33/7; N.S.A. 22 [1968] No. 25374). [2] Weaver, C. F.; Friedman, H. A; Hess, D. N. (ORNL-4254 [1968]129/34, 129). [3] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977]1149/63, 1150/1). [4] Krause, R. F., Jr. (Proc. Electrochem. Soc. 78-1 [1978] 199/209, 200/1). [5] Edwards, A. J.; Peacock, R. D.; Smail, R. W. H. (J. Chem. Soc. 19624486/91). [6] NuttaU, R. L.; Kilday, M. V.; Churney, K. L. (in:Douglas, T. B.; Beckett, C. W., AD-782028-5- GA [1974]1/123, 81; C.A 83 [1975] No. 16681). [7] OueUette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A.; Steven, AM. (Inorg. Syn.13 [1972]146/50). [8] Mercer, M.; Ouetlette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A (J. Chem. Soc. A 1969 2532/4). [9] Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970]113/5). [10] Weaver, C. F.; Friedman, H. A (ORNL-4191 [1967]142/3). [11] Opalovskii, A. A.; Khaldoyanidi, K. A. (U.S.S.R. 223083 [1967/72] from C.A 78 [1973] No. 6042). Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 97 [12] Gotkis, I. S.; Gusarov, A. V.; Pervov, V. S.; Butskii, V. D. (Koord. Khim. 4 [1978] 720/4; Soviet J. Coord. Chem. 4 [1978] 536/40). [13] Pervov, V. S.; Butskii, V. D.; Podzolko, L. G. (Zh. Neorgan. Khim. 23 [1978]1486/91; Russ. J. Inorg. Chem. 23 [1978] 819/22). [14] Falconer, W. E.; Jones, G. R.; Sunder, W. A.; Haigh, 1.; Peacock, P. D. (J. Inorg. Nucl. Chem. 35 [1973] 751/3). [15] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [16] Asprey, L. B.; Paine, R. T., Jr., United States Energy Research and Development Ad- ministration (U.S. 3929601 [1974/75]; C.A. 84 [1976] No. 124096). [17] O'DonneU, T. A.; Stewart, D. F. (J. Inorg. Nucl. Chem. 24 [1962] 309/14, 313). [18] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568/74,1569). [19] Opalovskii, A. A.; Khaldoyanidi, K. A.; Novosibirsk Institute of Inorganic Chemistry (U.S.S.R. 220973 [1967/72]; C.A. 78 [1973] No. 6041). [20] Peacock, R. D. (Proc. Chem. Soc. 1957 59). [21] O'DonneU, T. A.; Peel, T. E. (Inorg. Nucl. Chem. H. H. Hyman Mem. Vol. 1976, pp. 61/2; C.A. 85 [1976] No. 115925). [22] Opalovskii, A. A.; Anufrienko, V. F.; Khaldoyanidi, K. A. (Dokl. Akad. Nauk SSSR 184 [1969] 860/2; Dokl. Chem. Proc. Acad. Sci. USSR 184/189 [1969] 97/9). [23] McCaulay, D. A.; Higley, W. S.; Lien, A. P. (J. Am. Chem. Soc. 78 [1956]3009/11). [24] Blinova, O. V.; Predtechenskii, Yu. B. (Opt. Spektroskopiya 47 [1979] 1120/5; Opt. Spectrosc. [USSRj 47 [1979] 622/4). [25] Rychagov, A. V.; Korolev, Yu. M.; Pobedash, N. V. (Sb. MetaUurgiya i MetaUoved. Chist. Met. M 1975 No. 11, pp. 37/47, 39; C.A. 85 [1978] No. 48830). [26] Korolev, Yu. M.; Rychagov, A. V. (Izv. Akad. Nauk SSSR MetaUy 1978 No. 6, pp. 16/22; Russ. Met. 1978 No. 6, pp. 14/8). [27] O'DonneU, T. A.; Stewart, D. F. (Inorg. Chem. 5 [1966]143417). [28] Hargreaves, G. B.; Peacock R. D. (J. Chem. Soc. 1960 1099/103). [29] Fergusson, J. E. (Halogen Chem. 3 [1967] 227/302, 265). [30] Khaldoyanidi, K. A.; Opalovskii, A. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1973142/5; C.A. 79 [1973] No. 12985). [31] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [32] Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63, 359). [33] RusseU, J. L.; Jache, A. W. (J. Fluorine Chem. 7 [1976] 205/20, 208, 212/4). [34] Brownstein, S. (Can. J. Chem. 51 [1973] 2530/3). [35] Paine, R. T.; Asprey, L. B.; Graham, L.; Bartlett, N. (Inorg. Syn. 19 [1979]137/40). 2.2.7.2 The Moleeules (Monomer and Oligomers) Monomeric MoFs. For the MoFs molecule D3h symmetry is assumed [1 to 6,22]; symmetry close to D3h was assumed in [7]. Both D3h and C4V symmetries were considered in [8,9]. Assumed Mo-F distances are r= 1.80 [6], 1.83 [8,9], 1.84 [1,5] (see aLso [8, 9]), and 1.88 A [7]. AxiaL and equatoriaL bond Lengths of r = 1.79 and 1.82 A, respectiveLy, have been evaluated by [11] from vibrationaL spectra of liquid MoFs recorded by [12]. These r vaLues have been adopted by [3]. The caLcuLated product of the moments of inertia is Ix'ly'lz (in 10-114 g3· cm6)=44.78 (r = 1.84 A, D3h) [11]. For r = 1.83 A the vaLue is 43.5 and 37.2 for D3h and C4v, respectiveLy [8, 9]. For D3h the vaLue 36.7 was given [10], aLso see [22, 25]. Gmelin Handbook Mo Suppl. Vol. B 5 7 98 Molybdenum Fluorides The ground state was considered a doublet [1, 22], but an electronic degeneracy of four was assumed in [10]. The following table compares the force constants of MoFs predicted assuming D3h symme try [3] with force constants evaluated (by [11]) from vibrational spectra recorded on the condensed phase by [12] (for molecules in the laUer, D3h symmetry is questionable [11]). The K's (K1 = axial, K2 = equatorial) and H's are bond stretching and angle deformation force constants, the k's and g's are bond-bond interaction and bond-angle interaction force constants (for definition details of the internal coordinates see the paper [3]; all values in mdyn/A): K1 H1 k1 gl Ref. 4.7003 4.9269 0.5935 0.2760 0.5935 0.3864 0.2729 0.2077 0.1880 0.0956 [3] 4.5255 5.1106 0.4768 0.1215 0.5677 1.0064 0.0554 0.0030 -0.0002 [11] Ratios of the force constants have been calculated in [2] assuming D3h symmetry and using the theory from [13] ("TS") and that of [14] ("PHU"). (The Fij are related to symmetry coordi nates.) The theories of [13] and [14] yield different results only for F11 :F22 [2]: theory ...... F11 : F22 F13 : F33 F23 : F33 TS ...... 0.3039 0.2635 0.1522 PHU ...... 0.3346 0.2635 0.1522 Mean amplitudes of vibration have been calculated [4, 11] using the fundamental frequen cies reported in [12]. The following fundamental frequencies (in cm-1) have been reported for D3h symmetry (in parentheses: degeneracies; in brackets: unobserved vibrations): 759(1 x), 738(1 x), 683(1 x), [500(1 x)], 713(2x), 261(2x), 112(2x), [200(2x)] [1]. (These values are adopted by [26].) The laUer value [200(2x)] was replaced by 410(2x) in [17] and by 400(2x) in [22]. The following fundamentals (in cm-1) have been given in [9]: symmetry v1 Vg 692 580 346 550 278 295 654 411 214 742 655 760 484 761 309 188 345 The same frequency values have been given for C4v in [8]. The more recent values for D3h in [9] seem to revise the set of fundamental frequencies given for D3h in [8]. The effective charge q = 0.56 e on the Mo atom results from a calculation [5] by the method given in [15]. Using a mass spectrometer, beam deflection experiments were performed on the vapor over crystalline MoFs between room temperature and 55°C. Any permanent electric dipole moment of MoFs (and also of Mo2FlO) was below the sensitivity limit of -0.02 D of the beam deflection method used [16]. The electron affinity (EA) of MoFs was determined from ionization reactions occurring in crossed molecular beams (MoFa on one hand and Cs and CS2 atomic and diatomic beams on the other one). The inequality 3.3 ± 0.4 eV (with eV range Cs beams) < EA(MoFs) < 4.66 eV (with 5 to 20 eV range Cs beams) resulted [18]. From gas-phase reactions of MoF n with BeF2, BeF; and like species, EA(MoFs)=3.6±0.2eV [19] and 3.48eV are given in [33]. From the threshold of MoFsproduction in Na + MoFa crossed molecular beam experiments, EA(MoFs) ~ Gmelin Handbook Mo Suppl. Vol. B 5 MoF5 99 3.5 eV [20]. EA(MoF5»3.3 ±0.4 eV resulted from the MoFs production in eV-range Cs beams crossed with MoF6 beams [21]. Using thermal energy Cs beams, EA>3.03±0.4eV resulted [18,21]. Dimeric Mo2F10. The product of the moments of inertia is Ix 'Iy'I z = 3.68 x 10-111 g3. cm6 [10, 17,22], also see [25]. The symmetry number of the molecule is a = 4 [10, 22]. The electronic degeneracy is 1 according to [10], but 3 according to [17, 22]. The vibrational frequencies and degeneracies are 121 cm-1 (3x) and 90 cm-1 (3x) in addition to the monomer frequencies the degeneracies of which are to be doubled [17,22], also see [25]. No permanent electric dipole moment was detected [16] (see the monomeric species above). Trimeric Mo3F15. Ix'ly'lz = 95.7 x 10-111 g3. cm 6• Electronic degeneracy: 4. Fundamental fre quencies: 106 cm-1 (6x) and 53 cm-1 (6x) are to be added to the monomer frequencies the degeneracies of wh ich are to be tripled [17,22], also see [25]. An attempt was made to determine the molecular structure of M03 F15 by electron diffrac tion. The results rest on the (questionable) proposition that (according to mass spectroscopic studies by [23]) the vapor consisted mainly of trimers [24]. Mass Speclra (MS) MoF5 molecules under 72 eV electron impact yield the following mass spectrum [26]: species ...... Mo+ MoF~ MoF~ MoF: MoF! intensity ...... 20a) 30a) 40a) 150±50 100 a) assumed values The appearance potential (AP) of MoF! from the neutral parent MoF5 is AP = 10.81 ± 0.2 eV [26]. The following MS were recorded at 70 eV electron impact. At source temperatures trom 25 to 50°C the vapor over crystalline MoF5 yielded [16]: species ...... MoF~ MoF~ MoF: MoF! intensity ...... 0.42 0.43 1.00 0.06 At 45°C [16]: species Mo+ MoF+ MoF~ MoF~ MoF: MoF! intensity 0.0074 0.015 0.067 0.22 1.00 0.015 species ...... M02F~ M02F~ M03Ft4 M04Ftr M04Fts M04Ft9 intensity ...... 0.0022 0.26 0.017 0.00015 0.00025 0.00015 The following table compares the MS of vapors trom crystalline (Xtal) and supercooled liquid (SCl) MoF5, both at 296.4 K, under the impact of 60 eV electrons. The intensities of the ionic species are as follows [23]: species ...... MoF! MoF: MoF~ M02Fto M02F~ M02F~ SCl ...... 8.3 360 0.58 450 Xtal ...... 2 100 21 0.1 110 2.5 species ...... M03Ft5 M03Ft4 M03Ft3 M04F~ M04Ft9 M04Fts SCl ...... 25 86 2.7 Xtal ...... 6 17 0.5 0.07 0.4 0.01 GmeLin Handbook Mo Suppl. Vol. B 5 100 Molybdenum Fluorides In the vapor over crystalline MoFs at 296.4 K the following fragmentation reactions of metastable species occur (MoF: intensity = 100) [23]: reaction ...... M04Fi9-+ M03Fi4 + MoFs M03Fi4 -+ M02Ft + MoFs M02Ft-+ MoF: + MoFs intensity 0.1 0.5 0.05 The main species found in the MS with 70 eV electron impact on the vapor over solid MoFs at 25°C are MoFt(20), MoF:(155), MoF!(47), MoF~(24), and MoF+(10). Dimeric and trimeric species M02Fx and M03Fy {x and y not identified) were also found [27]. The abundancies of ionic species in the MS are certainly not those of the corresponding neutral species present in the vapor, see, e. g., the ease with which M02FlO is fragmented under electron impact [28], and also below. Attempts to elucidate the degree of association of the MoFs molecules in the vapor by MS yielded conflicting results (see above and also below). Those results were also in conflict with the combined vapor pressure and vapor density studies on saturated vapor described on p.105. Electron impact at 60 [23] and 70 eV [16, 27, 29] was used. The abundancies of the n-meric species produced in the MS were in the ratios (n=1): (n=2): (n=3): {n=4)=1 :0.20: 0.013 :0.0004 for the vapor over the solid at 48°C [16]. Ratios {n=3):{n=4):{n=5)=1 :0.065:0.0004 with negligible amounts of monomers and dimers were found in [30]. The saturated vapor over the solid at 323 K contains dimers, trimers, and tetramers. Monomers are not mentioned in the paper, but obviously also found [29]. In the 10-3 to 0.1 Torr pressure range, the vapor over liquid MoFs consists of -80% monomers, -20% dimers, and <1% trimers [31]. At 70°C, no oligomers were found [12]. The kinetics of the fragmentation in mass spectrometers was considered for the n-mers {MoFs)n in [22]. Taking the relative abundancies of the n = 1-, 2-, and 3-meric species from [16] and the combined vapor pressure and vapor density data from [32], the mole fractions Xl' X2' and X3 of the n = 1-, 2-, and 3-mers have been calculated for 298.15 K. The preferred xnvalues and their probable ranges are [22]: species ...... monomer dimer trimer preferred xn 0.027 0.94 0.035 range of X n 0.0002 to 0.10 0.86 to 0.97 0.02 to 0.05 References: [1] Douglas, T. B.; Krause, R. F., Jr.; Acquista, N.; Abramowitz, S. (AD-782094 [1974] 1/111, 50/4). [2] Sarkar, P. C.; Singh, G. C.; Srivastava, U. S. L. (Indian J. Phys. B 53 [1979] 278/81). [3] Ohwada, K. (Spectrochim. Acta A 37 [1981J 873/8). [4J Singh, B. P.; Pandey, A. N.; Singh, H. S. (Indian J. Pure Appl. Phys. 10 [1972J 283/6). [5J Pervov, V. S.; Fal'kengof, A. T.; Murav'ev, E. N. (Koord. Khim. 5 [1979] 155/8; Soviet J. Coord. Chem. 5 [1979] 117/20). [6] Orekhov, V. T.; Rybakov, A. G. (Zh. Fiz. Khim. 47 [1973]1612; Russ. J. Phys. Chem. 47 [1973] 916). [7] Spiridonov, V. P.; Romanov, G. V. (Vestn. Mosk. Univ. Khim. 24 No. 1 [1969]65/8; Moscow Univ. Chem. Bull. 24 No. 1 [1969] 51/3). [8] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Zh. Fiz. Khim. 44 [1970]2769/72; Russ. J. Phys. Chem. 44 [1970]1576/8). [9] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [10] Krause, R. F., Jr. (Proc. Electrochem. Soc. 78·1 [1978]199/209). Gmelin Handbook Mo Suppl. Vol. B S MoFs 101 [11] WendLing, E. J. L.; Mahrnoudi, S.; MacCordick, H. J. (J. Chern. Soc. A 1971 1747/54). [12] OueLLette, T. J.; RatcLiffe, C. T.; Sharp, D. W. A. (J. Chern. Soc. A 1969 2351/4). [13] Thirugnanasarnbandarn, P.; Srinavasan, G. J. (J. Chern. Phys. 50 [1969] 2467/75). [14] Peacock, C. J.; Heidborn, U.; MüLLer, A. (J. MoL. Spectrosc. 30 [1969] 338/44). [15] J0rgensen, C. K.; Horner, S. M.; HatfieLd, W. E.; Tyree, S. Y. (Intern. J. Quantum Chern. 1 [1967] 191/215). [16] FaLconer, W. E.; Jones, G. R.; Sunders, W. A.; VasiLe, M. J.; Muenter, A. A.; Dyke, T. R.; KLernperer, W. (J. FLuorine Chern. 4 [1974] 213/34, 218/27). [17] Brewer, L. (Proc. ELectrochern. Soc. 78-1 [1978]177/86). [18] Mathur, B. P.; Rothe, E. W.; Reck, G. P. (J. Chern. Phys. 67 [1977] 377/81). [19] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chern. Phys. 71 [1982]145/56). [20] Cornpton, R. N.; Reinhardt, P. W.; Cooper, C. D. (J. Chern. Phys. 68 [1978] 2023/36). [21] Rothe, E. W. (COO-2850-2 [1977]1/22; C.A. 88 [1978] No. 110896). [22] DougLas, T. B. (J. Chern. Thermodyn. 9 [1977] 1165/79). [23] Gotkis, I. S.; Gusarov, A. V.; Pervov, V. S.; Butskii, V. D. (Koord. Khirn. 4 [1978] 720/4; Soviet J. Coord, Chern. 4 [1978] 536/40). [24] Girichev, G. V.; Petrova, V. N.; Petrov, V. M.; Krasnov, K. S.; Goncharuk, V. K. (Izv. Vysshikh Uchebn. Zavedenii Khirn. Khirn. TekhnoL. 24 [1981] 131/2; C.A. 94 [1981] No. 148656). [25] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonaLd, R. A.; Syverud, A. N. (JANAF TherrnochernicaL TabLes, 3rd Ed. Pt. 11 [1985] 1155, 1169, 1171). [26] ALikhanyan, A. S.; StebLevskii, A. V.; MaLkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khirn. 23 [1978]1477/82; Russ. J. Inorg. Chern. 23 [1978] 814/7). [27] Paine, R. T.; Asprey, L. B. (Inorg. Chern. 13 [1974]1529/31). [28] KLeinschrnidt, P. D.; Lau, K. H.; HiLdenbrand, D. L. (J. Chern. Thermodyn. 11 [1979]765/72, 768/9). [29] VasiLe, M. J.; Jones, G. R.; FaLconer, W. E. (Intern. J. Mass. Spectrorn. Ion Phys. 10 [1972/73] 457/69, 462). [30] Gotkis, I. S.; Gusarov, A. V. (Deposited Doc.-SPSTL-397 Khp-D81 [1981]1/42 frorn C.A. 98 [1983] No. 41019). [31] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970]116/21). [32] Krause, R. F., Jr.; DougLas, T. B. (J. Chern. Thermodyn. 9 [1977]1149/63). [33] Borshchevskii, A. Ya.; Sidorov, L. N.; BoLtaLina, O. V. (DokL. Akad. Nauk SSSR 285 [1985] 377/81; DokL. Phys. Chern. Proc. Acad. Sci. USSR 280/285 [1985]1109/12). 2.2.7.3 Crystallographic Properties Crystalline MoFs is rnonocLinic with the Lattice parameters a = 9.61 ± 0.01, b = 14.22 ± 0.02, c = 5.16 ± 0.01 A, ß = 94°21' ± 20'. Space group C2/rn-C~h (No. 12), Z = 8 [1]. A List of observed and caLcuLated d vaLues is given in [2], for 2 evalues (agreement with the unit ceLL of [1] is stated) see [3]. The crystaL structure has been deterrnined by two-dirnensionaL (hkO and OkL) X-ray singLe crystaL fiLm rnethods. Refinernents Led to R vaLues not beLow 12% using individuaL isotropic ternperature factors. The atoms have been found to occupy the foLLowing equivaLent positions: Mo(1) on 4g (twofoLd axis); Mo(2), F(1), and F(2) on 4 i(rn); and F(3) through F(6) on the generaL 8 j position. The structure consists of fLuorine-bridged Mo-F octahedra forrning Gmelin Hrndbook Mo Suppl. Vol. B 5 102 Molybdenum Fluorides eyelie tetramers M04F20 of an alm ost square arrangement. For a sehematie drawing see the paper. The angles of the Mo-F-Mo bridges are 180° ± 2°, i. e., the Mo and bridging F atoms are in a planar arrangement. In the tetramerie unit there are three different Mo-F bond lengths: (1) about 1.85 ± 0.07 Afor the terminal Mo(l)-F distanees, (2) about 1.70 ± 0.1 0 Afor the terminal Mo(2)-F distanees, and (3) about 2.06 ± 0.04 Afor the Mo-F bridges. MoFs is isomorphous with NbFs (see "Niob" B 1,1970, p.136) and TaFs (see "Tantal" B 1,1970, p. 84) [1]. X-ray powder photographs eonfirmed isomorphism with TaFs and WFs [4]. The existenee of two polymorphie forms with a transition temperature of 21.1°C whieh had been dedueed trom studies of the MoFs-MoF6 system [10] eould not be eonfirmed later with pure samples [11]. Liquid and Glassy MoFs_ Liquid MoFs supercools and erystallizes only near O°C within several hours; above and below ~ O°C, praetieally no erystallization oeeurs [5]. At room temperature, the liquid does not solidify in less than 1 d [6] while the erystallization takes several hours with [7]. Also the color ehanges from dark brown (for the glass) to bright yellow (for the erystalline solid). This irreversible transition was studied also by X-ray diffraetion whieh showed the produet to be M04F20 . The glass-to-erystal transition hardly takes plaee outside the temperature range 224 to 273 K [2]. The ratio of the molar enthalpy of vaporization to the normal boiling temperature suggests a high degree of assoeiation for the liquid MoFs (by applieation of Trouton's rule) [12]. Liquid and glassy MoFs were studied by 19FNMR between 100 and 370 K at 10 kOe [8,9]. The glass was formed by quenehing the liquid to ~80 K [9]. At low temperatures the 19FNMR speetrum eonsists of broad features indieating rigid lattiee behavior. At rising temperature (above 215 K [8]) these features narrow due to orientational and translational diffusion [8]. Eventually, these features turn into two well-resolved lines whieh, with respeet to C6Fs, are shifted toward lower fields [8,9] by 484 and 207 ppm. The ratio of the intensities of 484 ppm line to 207 ppm line is elose to 1:4 between 220 and 310 K. This indieates a C4v strueture of the MoFs moleeules [8], also see [9]. When the glassy speeimen is kept for several hours at 224 to 273 K, the intensities of the narrow lines deerease and a broad line (ßH=6.5 Oe) appears (erystallization) [8]. At least below O°C the MoFs moleeules do not have the D3h (trigonal bipyramidal) strueture. However, inerease of temperature gradually broadens the lines referred to above. These also shift one toward another and, at 370 K, merge. The merged eondition might eorrespond to a trigonal bipyramidal (D3h ) strueture of the moleeules [8] as was dedueed from vibrational speetra at 25 and 80°C [6]. The strueture of the low-temperature glass (T~215 K) presumably eonsists of linear ehains of square pyramidal (C4v) moleeules linked by the F atoms at the top of the square pyramids [8]. References: [1] Edwards, A. J.; Peaeoek, R. D.; SmalI, R. W. H. (J. Chem. Soe. 19624486/91). [2] Khaldoyanidi, K. A.; Yakovlev, I. I. (Zh. Neorgan. Khim. 32 [1987] 1089/91; Russ. J. Inorg. Chem. 32 [1987] 610/2). [3] Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4254 [1968] 129/34). [4] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [5] Vasil'ev, Va. V.; Opalovskii, A. A.; Khaldoyanidi, K. A. (Izv. Akad. Nauk SSSR Sero Khim. 1969 271/5; Bull. Aead. Sei. USSR Div. Chem. Sei. 1969231/3). [6] Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A. (J. Chem. Soe. A 1969 2351/4). [7] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977]1149/63). [8] Panieh, A. M.; Goneharuk, V. K.; Gabuda, S. P.; Moroz, N. K. (Zh. Strukt. Khim. 20 [1979]60/2; J. Struet. Chem. [USSR] 20 [1979] 4517). Gmelin Handbook MoSuppl. Vol. B5 MoFs 103 [9] Goncharuk, V. K.; PoLishchuk, S. A.; Gabuda, S. P. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 226; C.A. 89 [1978] No. 206944). [10] Popov, A. P.; Tsvetnikov, A. K.; Goncharuk, V. K. (Zh. Neorgan. Khim. 23 [1978] 236/9; Russ. J. Inorg. Chem. 23 [1978] 132/3). [11] KhaLdoyanidi, K. A.; YakovLev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981]3067/9; Russ. J.lnorg. Chem. 26 [1981]1639/40). [12] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568/74). 2.2.7.4 Mechanical and Thermal Properties 2.2.7.4.1 Density The density of crystaLLine MoFs was measured in perfLuorofLuorene (obviousLy at room temperature): Dm = 3.44 g/cm3 ; Dx = 3.61 g/cm3 [1]. The vapor densities over Liquid MoFs have been measured by a fLow (entrainment) method (with MoF6 added to counteract disproportionation). Denoting with Pn the partiaL pressures of the n-mers, the foLLowing densities resuLted [2,3]: ~n' Pn in kPa [2] 0.12005 x (1 ± 0.0023) 0.3873 x (1 ± 0.0022) 1.1124x(1 ±0.0009) ~n' Pn in kPa [3] . . . .. 0.12118 x (1 ± 0.0022) 0.3896 x (1 ± 0.0028) 1.1284x(1 ±0.0025) T in K ...... 343.36 362.88 383.00 The relationship Ln(~n·Pn)=88.388-11026.4!T -10 LnT is given i!1 [3]. References: [1] Edwards, A. J.; Peacock, R. D.; SmaLL, R. W. H. (J. Chem. Soc. 19624486/91). [2] Krause, R. F., Jr.; DougLas, T. B. (J. Chem. Thermodyn. 9 [1977] 1149/63). [3] Krause, R. F., Jr. (Proc. ELectrochem. Soc. 78-1 [1978] 199/209). 2.2.7.4.2 Thermal Properties 2.2.7.4.2.1 Melting. Boiling. Vaporization Melting. With very pure sampLes the meLting point 45°C was determined [1] in good agreement with the vaLue 45.0 ± 0.5°C which was measured thermographicaLLy as weLL as visuaLLy in a thin-waLLed quartz capiLLary [2]. The meLting temperature 46°C is given in [13]. MeLting curves against time, measured with sampLes of cryoscopic impurity -0.15 moL%, estabLished the meLting temperature at zero impurity to be 318.82 K (45.67°C) [3, 4].ln addition, aseries of vaLues has been reported which are about 20 K higher: 63 [5],64 [6], 65 [7], 67 [8, 9], and 67.4°C [10]. It has been presumed that the lower value may be the melting point of the metastabLe vitreous form of MoFs [10]. More LikeLy, the higher vaLues may refLect the existence of solid soLutions with MoOF4 (m.p. 98°C) in these sampLes [1 to 3] (see the equiLibrium dia gram of the MoFs-MoOF4 system on p. 204). The rather constant upward shift by -20 K of the meLting temperature wouLd suggest that an azeotropic mixture is distiLLed in the purification steps of sampLe preparation. Liquid MoFs exhibits substantiaL supercooLing. Standing at room temperature for a few hours [3] or 2 to 3 d [11] is necessary for crystaLLization. In a quartz ampuLe the meLt does not Gmelin Handbook Mo Suppl. Vol. B 5 104 Molybdenum Fluorides crystaLLize at room temperature within a week or more, while at the temperatures of dry ice and Liquid nitrogen it soLidifies to a gLassy state [2, 12]. The gLass to Liquid transition is said to occur at 240 K (?) [13]. From fraction meLted vs. time curves (at known power input), the enthaLpy of meLting ßHm= 6.1 kJ/moL±5% [3], aLso see [4]. A strongLy deviating vaLue, ßHm= 12.9 kcaUmoL, was obtained from soLubiLity measurements of MoF5 in hexachLorobuta-1,3-diene [14]. ßHm/R = 730 ± 40 K [15], [16, p. 53]. Boiling. The Liquid compound begins to disproportionate to MoF6 and MoF4 beLow its boiLing point, see p. 112. By extrapoLation of vapor pressure data, the boiLing temperature was caLcuLated as 211 [9], ~ 212 [7], and 213.6°C [8]. With regard to the MoF6 vapor pressure of 0.05±0.03 atm, caLcuLated for Liquid MoF5 saturated with MoF4, an atmospheric boiLing point of 540 ± 10 K (267°C) was obtained [15]. Vaporization. CrystaLLine MoF5 sublimes near 50°C [5]. The very Low sublimation pressure couLd not be measured accurateLy with the static methods used [8]. The p(MoF5) = 2 Torr at 65°C (soLid) [9]. The subLimation pressure was measured mass spectrometricaLLy. At 300.3 K, the main gas-phase species, M03F15 and M04F20 , occur with partiaL pressures (in 10-6 atm) of 4 and 0.26, respectiveLy [17]. The enthaLpy of sublimation at 298.15 K, ß~uJR=18000K, has been derived for the monomer [18], 17700 ± 1000 K [16, p. 50]. For the dimer and the trimer, ß~uJR = 9544 ± 250 K and 11700±1000 Kare given, respectiveLy [16, pp. 51/2]. At 298.15 K, ß~ub=22.1 ±1.2 and 23.9 ± 2.0 kcaUmoL for trimers and tetramers, respectiveLy, according to mass spectrometric resuLts [17]. ßHsub = 86 kJ/moL was estimated in [19]. The mass spectroscopic study of the sublimation of MoF5 yieLded the foLLowing resuLts for the entropy and free energy of subLima tion: for the reaction 3 MoF5(s):;::::: M03F15(g), ßS~Ub.29815 = 48.9 ± 4.0 caL· moL-1. K-1 and ßG;ub.298.15=7.5±0.3 kcaUmol. For the reaction 4 MoF5(s):;:::::M04 F20(g), ßS~ub.298.15=49.4±5.7 caL·moL-1·K-1 and ßG;Ub.298.15=9.1 ±0.3 kcaUmoL [17]. The vapor pressure of Liquid MoF5 (with MoF6 added to counteract decomposition) was measured by a static method. The sum of the partiaL pressures of the n-mers, IPn (in kPa) = 0.360 x (1 ± 0.052) and 0.844 x (1 ± 0.015) at T = 373.0 and 392.5 K, respectiveLy [3]. EarLier, 11.62 to 12.90 Torr were determined at 392.6 K [20]. At 400 K, the totaL vapor pressure is 1000 Pa [18]. The vapor pressure was measured between 70 and 160°C. With p in Torr and T in K, it foLLows the relationship Log p = 8.58-2772/T [8]. This (high) resuLt was chaLLenged in [17] and attributed to the presence of impurities (MoOF4 ?) [3]; aLso see [21]. The enthaLpy of vaporization ßHvap = 12.37 kcaUmoL was derived from the vapor pressure curve of Liquid MoF5 [8] (note that these studies might have been fLawed by impurities, see above). Mi~ap = 20 kJ/moL was estimated for 298 K by [19]. For the monomer, ßH~ap.2981JR =17000 K [18], much more than the ßH=17 to 22 kcaUmoL (preferred vaLue: 19 kcaUmoL) derived with respect to the supercooLed Liquid by [22]. The difference between [18] and [22] was attributed to the difficuLties in estimating the abundance of monomers (n=1) in the MoF5 vapor [18]. ßH~ap(n=1)=137±42 kJ/moL [4]. For the dimer, ßH~ap(n=2)=15 to 16 kcaUmoL (preferred vaLue: 15.7 kcaUmoL) [22]. From the temperature dependence of the dimer partiaL pressure, ßH~ap (n=2) =66.89 kJ/moL at 298.15 K (and ß~ap(n=2) = 133.86 J. moL-1. K-1) [4]. For the trimer, at 298.15 K, ßH~ap (n=3) = 16 to 21 (preferred vaLue: 17.7) kcaUmol. The free energies of vaporization (with respect to the supercooLed Liquid at 298.15 K) are ßGvap (n=1) = 7.5 to 11.5 (preferred vaLue: 8.5) kcaUmoL, ßGvap (n=2) = 6.45 to 6.51 (preferred vaLue: 6.48) kcaUmoL, and ßGvap (n=3) = 8.1 to 8.7 (preferred vaLue: 8.4) kcaUmoL for monomer, dimer, and trimer vaporiza tion, respectiveLy [22]. Gmelin Handbook Mo Suppl. Vol. B 5 MoF5 105 For the vapor, frorn eornbined vapor pressure and vapor density deterrninations an average degree of assoeiation The reaetion Mo2F10(g):;::::::2MoF5(g) oeeurs in the vapor over disproportionating MoF3 and was studied by rnass speetrornetry (MS). Assurning an entropy of reaetion of ßS = 37 ± 4 eaL· rnoL-1 . K-1, the enthaLpy of reaetion ßH~8 = 44.6 ± 5.5 keaVrnoL was evaLuated [24]. ßH~8.15/R ""26000 K (i.e., ßHm15 =51.7 keaVrnoL) aeeording to the MS study [18]. ßHm =28 keaVrnoL were found in the earLy MS study [21]. For Mo3F15(g):;::::::3MoF5(g), the vaLue ßH=34 keaVrnoL is given in the earLy paper [21]. References: [1] KhaLdoyanidi, K. A; YakovLev, L 1.; Ikorskii, V. N. (Zh. Neorgan. Khirn. 26 [1981]3067/9; Russ. J. Inorg. Chern. 26 [1981]1639/40). [2] VasiL'ev, Va. V.; OpaLovskii, A A.; KhaLdoyanidi, K. A. (Izv. Akad. Nauk SSSR Sero Khirn. 1969 271/5; BuLL. Aead. Sei. USSR Div. Chern. Sei. 1969 231/3). [3] Krause, R. F., Jr.; DougLas, T. B. (J. Chern. Thermodyn. 9 [1977]1149/63, 1152/3). [4] Krause, R. F., Jr. (Proe. ELeetroehern. Soe. 78-1 [1978]199/209, 201). [5] Paine, R. T.; Asprey, L. B. (Inorg. Chern. 13 [1974]1529/31). [6] Peaeoek, R. D. (Proe. Chern. Soe. 195759). [7] Weaver, C. F.; Friedrnan, H. A. (ORNL-4191 [1967]142/3). [8] Cady, G. H.; Hargreaves, G. B. (J. Chern. Soe. 1961 1568/74, 1570). [9] Edwards, A. J.; Peaeoek, R. D.; SmaLL, R. W. H. (J. Chern. Soe. 19624486/91,4486). [10] Popov, A. P.; Tsvetnikov, A K.; Goneharuk, V. K. (Zh .. Neorgan. Khirn. 23 [1978] 236/9; Russ. J. Inorg. Chern. 23 [1978]132/3). [11] Mereer, M.; OueLLette, T. J.; Ratcliffe, G. T.; Sharp, D. W. A (J. Chern. Soe. A 1969 2532/4). [12] OpaLovskii, A. A.; KhaLdoyanidi, K. A. (Izv. Akad. Nauk SSSR Sero Khirn. 1973279/82; BuLL. Aead. Sei. USSR Div. Chern. Sei. 22 [1973] 270/2). [13] Ikorskii, V. N.; KhaLdoyanidi, K. A (Zh. Strukt. Khirn. 23 No. 2 [1982]151/3; J. Struet. Chern. [USSR] 23 [1982] 302/4). [14] GaLkin, N. P.; Bertina, L. E.; Orekhov, V. T.; PakLenkov, E. A. (Zh. Fiz. Khirn. 49 [1975]2454; Russ. J. Phys. Chern. 49 [1975]1443). [15] Brewer, L. (Proe. ELeetroehern. Soe. 78-1 [1978]177/86,181). [16] Brewer, L.; Larnoreaux, R. H. (At. Energy Rev. Spee. Issue No. 7 [1980]11/191, 46/58). [17] Gotkis, I. S.; Gusarov, A. V.; Pervov, V. S.; Butskii, V. D. (Koord. Khirn. 4 [1978] 720/4; Soviet J. Coord. Chern. 4 [1978] 536/40). [18] KLeinsehrnidt, P. D.; Lau, K. H.; HiLdenbrand, D. L. (J. Chern. Therrnodyn.11 [1979]765/72). [19] Dittrner, G.; Niemann, U. (Mater. Res. BuLL. 18 [1983] 355/69). [20] DougLas, T. B.; Krause, R. F., Jr. (AD-782028 [1974]110 + XIII pp., 90/110). [21] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970]116/21). [22] DougLas, T. B. (J. Chern. Thermodyn. 9 [1977]1165/79, 1178). [23] FaLeoner, W. E.; Jones, G. R.; Sunder, W. A.; VasiLe, M. J.; Muenter, A A.; Dyke, T. R.; KLernperer, W. (J. FLuorine Chern. 4 [1974] 213/34). [24] ALikhanyan, A. S.; Pervov, V. S.; MaLkerova, I. P.; Butskii, V. D.; Gorgoraki, V. L (Zh. Neorgan. Khirn. 23 [1978]1483/5; Russ. J. Inorg. Chern. 23 [1978] 817/8). Gmelin Handbook Mo Suppl. Vol. B 5 106 MoLybdenum FLuorides 2.2.7.4.2.2 Thermodynamic Data The heat capacity C~. 298 = 36 ± 2 caL· moL-l . K-l has been obtained for solid MoF5 from various Literature data. C~ increases up to 38 caL· moL-l. K-l at the meLting point (318.82 K). For Liquid MoF5, C~=37.2 caL·moL-l·K-l [13]. The C~ was caLcuLated for the ideaL monomeric gas, C~.298 = 24.195 caL· moL-l. K-l [1]; by the rigid rotor-harmonie osciLLator modeL and assuming r(Mo-F) = 1.80 A with D3h symmetry: C~.298= 23.103 caL· moL-1. K-l [2]. C~.298 = 102.763 J. moL-1. K-1 (~24.560 caL· moL-l. K-l) [3,13]. For the gaseous dimeric Mo2F10, C~.298= 212.349 J. moL-l. K-l (~50.751 caL· moL-1. K-l) and for the trimeric Mo3F15, C~.298 = 326.335 J. moL-l. K-l (~77.994 caL· moL-1. K-l) [3]. VaLues for temperatures between 0 and 6000 Kare Listed in the papers [1,3], for 500 to 3000 Kin [13]. The standard entropy S2s8 = 51 ± 15 caL' moL-1. K-1 has been estimated by semi-empiricaL methods for the crystaLLine solid [4]. Later S2s8 = 42.7 ± 3 caL' moL-1. K-l has been evaLuated from various Literature data. So increases up to 45.2 caL· moL-l. K-l at the meLting point (318.82 K). For Liquid MoF5, SO=49.8 caL·moL-1.K-l at this temperature and increases up to SO=73.3 caL·mol-1.K-l at 600 K [13]. For the ideaL gas of monomers, by the rigid rotor-harmonie osciLLator approximation S2s8=343±8 [5], 349.3 [6],347.655 J·moL-l·K-l [3] have been caLcuLated. S2ss=83.170 caL· moL-1. K-1 has been caLcuLated [1], 78.29 assuming D3h symmetry [2], 78.56 (obviousLy revising the 79.79 given in [8]) for D3h and 79.66 caL· moL-1. K-l assuming C4v symmetry (obviousLy revising the80.28 caL· moL-1. K-1given in [8]) [7]. Forthe method used in [8], see [9]. For tabLes giving caLcuLated So vaLues, see for T = 0 to 6000 K [1, 3], 100 to 1200 K [6], and 400 to 5000 K [7,8]. For the dimer Mo2FlO, S29S=530±25 J·moL-1.K-l according to the rigid rotor-harmonie osciLLator approximation [5]; S298 = 531.554 J. moL-l. K-l [3]. For the ideaL gaseous Mo3F15, S2s8 = 706.844 J. moL-1. K-l [3]. VaLues for Mo2FlO and Mo3F15 between 0 and 6000 Kare Listed in [3], for 300 to 1100 K in [13]. For solid MoF5, -(Go-Hm)fT increases from 42.7 at 298.15 K to 42.8 caL· moL-1. K-1 at the meLting point (318.82 K). For Liquid MoF5, the vaLue increases from 42.8 at the meLting point to 52.2 caL' moL-1. K-l at 600 K [13]. For the gaseous monomeric MoF5, For the ideaL gaseous Mo2FlO and Mo3F15, the vaLues for -(Go-H298)fT are Listed between o and 6000 Kin [3], between 300 and 1100 Kin [13]. Thermodynamic Oata of Formation. By soLution caLorimetry ~Hf [MoF5(s)] was determined using a soLution of HF containing Xe03 and comparing the heat effect with that of the dissoLution of Liquid MoF6 in a simiLar soLution; ~Hf[MoF5(S)] = -1395.74 ± 4.6 kJ/moL (~-333.59±1.1 kcaVmoL) resuLts [11]. By hydrolysis caLorimetry using aqueous NaOH and NaOCL at 298.2K, ~Hf[MoF5(S)]=-1387 kJ/moL resuLts [12]. With these data the earLier estimate - 340 ± 15 kcaVmoL, arrived at by semi-empiricaL methods, agrees rather weLL [4]. ~Hf.298/R=-167000±500 K is estimated for the soLid in the review [13]. The difference ~Hf[MoF5(S)]- ~Hf[MoF6(L)] by soLution caLorimetry is 189.79 ± 4.6 kJ/moL (~45.36±1.1 kcaVmoL) [11]. Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 107 For the monomer in the gas phase, ~Hf.298[MoFs(g)] = - 296.7 ± 2.0 kcaVmol [14] (±8.6 kcaV mol [15], also see [16]) has been derived for the reaction Mo(s) + 2.5 F2(g) ~ MoFs(g) by mass spectrometric (MS) studies of gas phase equilibria [14,15]. Also by MS, ~Hf.298[MoFs(g)]/R = -149300 ± 500 K [17] (±600 Kare given in the review [13]). The ~Hf values between 0 and 6000K are listed in [3]. ~Gf.298=-1185.363 kJ/mol,log K'.29S=207.671; values for ~Gfand log I For the formation of gaseous dimers and trimers from solid Mo plus gaseous F2, ~Hf.mlR = - 324460 ± 1000 K for the dimer and - 489000 ± 2500 K for the trimer have been estimated [13]. The ~Hfvalues between 0 and 6000 Kare listed in [3]. For the ideal gaseous M02FlO, ~Gf.298 = - 2536.961 kJ/mol, log K'.298 = 444.465 and for M03F1S, ~Gf.298 = - 3797.290 kJ/mol, log K'.298=665.269. Va lues for ~Gfand log K, between 0 and 6000 Kare listed in [3]. References: [1] Douglas, T. B.; Krause, R. F.,Jr.;Acquista, N.; Abramowitz, S. (AD-782094 [1974]1/111, 50/4). [2] Orekhov, V. T.; Rybakov, A. G. (Zh. Fiz. Khim. 47 [1973]1612; Russ. J. Phys. Chem. 47 [1973] 916). [3] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. (JANAF Thermochemical Tables, 3rd Ed. Pt. 11 [1985] 1155, 1169, 1171). [4] Rychagov, A. V.; Korolev, Yu. M.; Bratishko, V. D.; Rakov, E. G. (Tr. Inst. Mosk. Khim. Tekhnol. Inst. No. 62 [1969] 52/6). [5] Krause, R. F., Jr. (Proc. Electrochem. Soc. 78-1 [1978] 199/209). [6] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982]145/56). [7] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144). [8] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Zh. Fiz. Khim. 44 [1970]2769/72; Russ. J. Phys. Chem. 44 [1970] 1576/8). [9] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Khim. Vys. Energ. 4 [1970] 512/8; High Energy Chem. [USSR] 4 [1970] 462/7). [10] Brewer, L. (Proc. Electrochem. Soc. 78-1 [1978]177/86). [11] Nuttall, R. L.; Kilday, N. V.; Churney, K. L. (AD-782028 [1973] 110 + XIII pp., 78/89). [12] Burgess, J.; Haigh, 1.; Peacock, R. D. (J. Chem. Soc. Dalton Trans. 1974 1062/4). [13] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec.lssue No. 7 [1980]11/191,46,50/3). [14] Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63). [15] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [16] Hildenbrand, D. L.; Lau, K. H.; Brittain, R. D. (AD-A-097352 [1981]1/69, 17). [17] Kleinschmidt, P. D.; Lau, K. H.; Hildenbrand, D. L. (J. Chem. Thermodyn.11 [1979]765/72). 2.2.7.5 Electrical and Magnetic Properties The electrical conductivity 0 (in !lS/cm) of liquid MoFs increases from 0.432 at 345.4 K to 4.63 at 423.2 K. It follows the Arrhenius-type relationship 0 = 0 0 x exp( - E/RT) with 0 0 = 0.1536 S/cm and E = 8.7 kcaVmol [1]. The magnetic susceptibility X of both equilibrium (crystalline and liquid) and nonequili brium (glassy and supercooled, liquid) MoFs was measured by the Faraday method in the temperature range 78 to 473 K in fields between 5 und 12 kOe (the described susceptibility calibration is questionable) [2]. With a similar setup X was measured between 4.33 and 340 K. Gmelin Handbook Mo Suppl. Vol. B 5 108 Molybdenum Fluorides The applied diamagnetic correction was - 67 x 10-6 cm3 per g-formula [3]. X is plotted vs. T between 4 and 340 [3], 80 and 450 [2], 80 and 285 [4], and 140 and 340 K [5]. X increases sharply on melting at 318 K [2] (ßX"'" 30% at 390 K [3]), the step ßX occurring over an interval ß T = 4 K which is not due to temperature gradients [2]; for the step ßX also see [5]. For crystalline MoFs (consisting of M04 F20 moieties) there is a broad maximum in X around 240 K [2, 3] (-630 x 10-6 cm3/g-formula near 230 K [4]). On cooling, X passes a minimum at ::::;60 K and increases strongly on further cooling to below -50 K. This latter increase is ascribed to the presence of -4.1 % monomers and trimers. 8elected Xvalues (in 10-6 cm3 per g-formula) [3]: Xmol ...... 2904 354.7 651.4 639 Tin K ...... 4.33 60 240 300 The magnetic behavior of the crystalline solid is approximately modelIed by spin V2 moments at the corners of square M04F20 moieties, the moments being coupled antiferromag netically to their right and left neighbors (on the same square) by the exchange constant - 2 J = 21 0 cm-1 [2, 3], the 9 value being 2 [2] or 1.947 [3]. Liquid and glassy MoFs show Curie-Weiss type X vs. T behavior. Both forms follow the same formula, valid in the studied range from -80 to -450 K: X=[.l~f/(3ks·[T+150K]) with [.leff = 1.78 [.ls (the values are corrected for diamagnetism) [2]. The Curie-Weiss constant C=0.39 and 8= -146 Kare given for T>80 K [3]. But below 80 K, X deviates from this relationship and only in the 6 to 20 K range was Curie-Weiss type behavior again found, however, with the parameters C = 0.0777 and 8 = - 3.9 K. X(T) passes a maximum at 4.65 K. 8elected X values (in 10-6 cm3/mol, corrected for diamagnetism) of glassy and liquid MoFs are the following [3]: Xmol ...... 9346 9653 7558 3293 1900 1458.4 1015.8 801.1 Tin K ...... 4.33 4.65 7.0 20 60 120 240 340 NMR. Bridge and terminal F atoms are distinguished in the 19F NMR spectra recorded at 48, 75, and 153 K on crystalline MoFs' These spectra consist of two lines having the intensity ratio 1: 4 (corresponding to one bridging and four terminal F atoms per MoFs). The resonance frequency of the terminal F atoms does not significantly vary with temperature, but the resonance of the bridging F atoms shifts by 14 to 15 Oe toward lower fields as T decreases from 153 to 48 K (with the mean field 10500 Oe used, this corresponds to a shift by >1300 ppm) [6]. With the singlet state of the M04 F20 clusters (T~50 K) the local fields öH on the terminal and bridging F atoms are weaker by - 4 and -12 Oe than those measured on 19F in liquid C6 F6 (i. e., the low-field shifts are -380 and -1140 ppm for terminal and bridging F atoms, respectively) [6]. The temperature dependence of the local field at the bridging 19F nuclei follow the relationship ßH=öH+A·<8z >.(yl'l)-1, <8z> being the ensemble average of the projected cluster electron spin, y being the gyromagnetic ratio of 19F, and A = - (8 ± 1) x 10-4 cm-1 being the hyperfine interaction constant. With respect to <8z> note that the first excited state, a triplet separated by 2 J trom the ground state singlet, starts to fill at T~0.3 J/ks=50 K [6]. In the 8 = 0 state the bridging F nuclei are subjected to an additional field of -8 Oe which is not related to the electron spin paramagnetism. For 8 ~ 1 these nuclei are subjected to a negative isotropic hyperfine field related perhaps to a mixing of F2s electrons into the empty Mos+ eg orbitals [6]. For further NMR results, see p. 102. Gmelin Handbook Mo Suppt. Vol. B S MoF5 109 References: [1] Opalovskii, A. A; Khaldoyanidi, K. A (lzv. Akad. Nauk SSSR Sero Khirn. 1973 279/82; Bull. Aead. Sei. USSR Div. Chern. Sei. 1973 270/2). [2] Vasil'ev, Va. V.; Opalovskii, A. A; Khaldoyanidi, K. A (Izv. Akad. Nauk SSSR Sero Khirn. 1969 271/5; Bull. Aead. Sei. USSR Div. Chern. Sei. 1969 231/3). [3] Ikorskii, V. N.; Khaldoyanidi, K. A. (Zh. Strukt. Khirn. 23 No. 2 [1982]151/3; J. Struet. Chern. [USSR] 23 [1982] 302/4). [4] Khaldoyanidi, K. A; Vakovlev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khirn. 26 [1981] 3067/9; Russ. J. Inorg. Chern. 26 [1981]1639/40). [5] Khaldoyanidi, K. A; Ikorskii, V. N.; Grarnkina, Z. A (Zh. Strukt. Khirn. 17 [1976]364/6; J. Struet. Chern. [USSR] 17 [1976] 315/7). [6] Panieh, A. M.; Moroz, N. K.; Gabuda, S. P. (Fiz. Tverd. Tela [Leningrad]17 [1975]2433/5; Soviet Phys.-Solid State 17 [1975]1611/2). 2.2.7.6 Optical Properties 2.2.7.6.1 Color. Refractive Index. Electronic Spectra Color. Crystalline MoF5 is yellow [1 to 4], lernon yellow [5], light yellow [6]; also see [7]. MoF5 powder has a greenish yellow tint [8]. Liquid MoF5 is also yellow [9 to 11], but glassy MoF5 is dark brown ~nd turns to bright yellow on erystallization [12], also see [13, 14]. 0 Refraetive Index. Crystalline MoF5 is optieally biaxial with optie angle 90 • Refraetive indices: na =1.520, nß=1.534, ny =1.548 [5]. Eleetronie Speetra. Molten MoF5 at 66°C as weil as MoF5 dissolved in MoFs at 25°C show one symmetrie absorption band at 7500 ern-1 in the 4000 to 26000 ern-1 range. The absorption band (absorbanee: 0.28 at 0.1 rnrn pathlength in presurnably motten MoF5) is aseribed to a transition 2A;~2E' of the d1 system in a trigonal bipyrarnidal ligand eonfiguration [15]. Absorption around 1.26 f.lrn (~7940 ern-1) and an "intense shoulder" in the UV near 0.34 f.lrn (~29410 ern-1) have been found (presurnably with erystalline MoF5) [5]. References: [1] Peaeoek, R. D. (Proe. Chern. Soe. 195759). [2] Edwards, A. J.; Peaeoek, R. D.; Small, R. W. H. (J. Chern. Soe. 19624486/91). [3] Faleoner, W. E.; Jones, G. R.; Sunder, W. A.; Vasile, M. J.; Muenter, A. A.; Dyke, T. R.; Klernperer, W. (J. Fluorine Chern. 4 [1974] 213/34, 218). [4] Paine, R. T.; Asprey, L. B. (Inorg. Chern. 13 [1974]1529/31). [5] Weaver, C. F.; Friedrnan, H. A; Hess, D. N. (ORNL-4229 [1968] 33/7; N. S. A. 22 [1968] , No. 25462). [6] Nuttall, R. L.; Kilday, N. V.; Churney, K. L. (AD-782028 [1973] 110 + XIII pp., 78/89). [7] Aequista, N.; Abrarnowitz, S. (J. Chern. Phys. 58 [1973] 5484/8). [8] Faleoner, W. E.; Jones, G. R.; Sunder, W. A; Haigh, 1.; Peaeoek, P. D. (J. Inorg. Nuel. Chern. 35 [1973] 751/3). [9] Mereer, M.; Ouellette, T. J.; Rateliffe, C. T.; Sharp, D. W.A. (J. Chern. Soe. A 1969 2532/4). [10] Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W.A.; Steven, AM. (Inorg. Syn. 13 [1971]146/50). [11] Krause, R. F., Jr.; Douglas, T. B. (J. Chern. Thermodyn. 9 [1977]1149/63). [12] Panieh, AM.; Goneharuk, V. K.; Gabuda, S. P.; Moroz, N. K. (Zh. Strukt. Khirn. 20 No. 1 [1979] 60/2; J. Struet. Chern. [USSR] 20 [1979] 45/7). Gmelin Handbook Mo SuppL VoL B 5 110 MoLybdenum Fluorides [13] DougLas, T. B.; Beckett, C. W. (AD-782028-5-GA 19741/123, 81; C. A. 83 [1975] No. 16681). [14] O'DonneLL, T. A.; PeeL, T. E. (lnorg. NucL. Chem. H. H. Hyman Mem. VoL. 197661/2). [15] Peacock, R. D.; SLeight, T. P. (J. FLuorine Chem. 1 [1971/72] 243/5). 2.2.7.6.2 Vibrational Spectra Crystalline MoF5. Based on the C2h seLection ruLes, for crystaLLine MoFs, 36 K = 0 modes are expected as Raman active, the remaining 33 K = 0 modes as IR active. The nonequivaLent Mo atoms on Cs and C2 sites of the M04F20 units imply two-site splittings in the vibrationaL spectra [6]. Both D3h and C4v symmetry are consistent [1] with the vibrationaL spectra pubLished by [1, 6]. The IR spectrum of solid MoFs (apparentLy a film formed by quenching the vapor from subLiming MoFs) was measured at 20 K between 400 and 750 cm-1 [1]. The IR spectrum recorded between 400 and 1800 cm-1 at 77 K from such a fiLm is plotted for upto -1100 cm-1 in [5]. Raman and IR spectra were recorded at 25°C [4]. The Raman study [4] was repeated between 150 and 800 cm-1 at improved resoLution (ßv = 2cm-1) and the resuLts of [4] were cLoseLy confirmed by [6], but subtLe differences exist: the band near 563 cm-1 found by [4] was not observed by [6] whereas new absorption bands were detected at 332, 436, and 494 cm-1 [6]. The foLLowing frequencies are given in [4]: Raman shift in cm-1 .••.•• 198 s 241 s 250 sh 294 w 406 w IR frequency in cm-1 ..... 160 m 200 m Raman shift in cm-1 ••.•.• 563 w 696 vs 704 s IR frequency in cm-1 ..... 480 vw 520 w 647 vs 698 vs Raman shift in cm-1 •.•••• 737 vs a) 746 sh 759 vs IR frequency in cm-1 ..... 745 vs 845 w 890 w 970 w a) From MoF6?, see foLLowing tabLe from [1]. The vibrationaL spectra recorded at 20 Kare Listed with a tentative assignment in D3h [1]: Raman shift in cm-1 59 127 181 198 236 250 288 IR frequency in cm-1 assignment ...... poLymer or v7(E') externaL vibr. Raman shift in cm-1 400 494 683 696 IR frequency in cm-1 525 660 700 assignment ...... bridge v3(A2) poLymer bond Raman shift in cm-1 704 (736) 746 758 IR frequency in cm-1 725 assignment ...... poLymer v3(MoF6) - poLymer Gmelin Handbook Mo Suppl. Vol. B 5 MoF5 111 The Raman shifts measured at 25°C were assigned assuming the molecular symmetry D3h as follows [6]: shift in cm-1 ...... 181 w 199 m 239 m 252 m 282 symmetry type in the crystal ...... Ag Ag Ag Ag symmetry type in the moleeule ..... v7(E/) v7(E/) ?v6(E/)? v6(E/) shift in cm-1 ...... 332 402 436 w 494 vw 684 w symmetry type in the crystal ...... symmetry type in the moleeule ..... vs(E") v4(A2) v3(A2) shift in cm-1 ...... 696 m 706 m 7385 747 m 7595 symmetry type in the crystal ...... Ag Ag Ag Ag symmetry type in the moleeule ..... v2(A;) v2(A;) v1(A;) v5(E/) v1(A;) (For the correlation diagram connecting the determined symmetry species of the crystal with the assumed symmetry species of D3h molecules, see the paper [6]). IR spectra between -220 and -900 cm-1 show absorption maxima at 234, 258, 312, 515, 690, and 750 cm-1 [8]. Absorption bands at 521 (m), 654 (sh), 691 (5),739 (m), and 765 (w) cm-1 are found [5]. The 515 [8] (521 [5]) cm-1 vibration is attributed to Mo-F-Mo bridging bonds [5, 8]. Vibrations of the bridging F atoms forming the corners of the M04F20 units are tentatively associated with the 287, 332, and 402 cm-1 Raman shifts observed [6]. The 690 and 750 cm-1 IR frequencies are attributed to terminal Mo-F bonds [8] as were the 738 and 759 cm-1 Raman shifts [7]. The following observed vibrational frequencies have been assigned to polymerie species [1]: V in cm-1 ...... 59 227 231 703 sample ...... crystal melt matrix melt method ...... Raman Raman IR Raman v in cm-1 ...... 704 716 748 768 sampIe ...... matrix matrix melt matrix method ...... IR IR Raman IR Liquid MoFs. With the melt, Raman shifts in the 40 to 800 cm-1 range have been observed as follows (assignments assuming D3h molecular symmetry) [1]: Raman shift in cm-1 ... 125 201 227 287 440 703 748 assignment ...... v7(E/) - polymer v6(E/) polymer polymer Raman spectra from a "premelted", rapidly cooled sampIe (supercooled liquid?) held at 30°C show the following shifts (in cm-1): 200 (w), 228 (w), 701 (w, poL), and 747 (5, pol.) [5]. With the supercooled liquid the following Raman shifts (in cm-1) and IR frequencies (in cm-1) are found and assigned assuming D3h symmetry for the MoF5 moleeules [4]: Raman shift ...... 201 231 440 w, br IR frequency ...... 205 250 br assignment ...... v7(E/) v6(E/) vs(E") Raman shift ...... 703 pol. 747 pol. IR frequency ...... 500 br 685 730 assignment ...... v4(A2) v3(A2) v2(A;) v5(E/) v1(A;) Gmelin Handbook Mo Suppl. Vol. B 5 112 Molybdenum Fluorides Vapor. The IR spectrum of the vapor over MoFs heated at 44 to 85°C is plotted in [3] for v=400 to 1200 cm-1• Bands attributed to MoFs occur at 510,770, and -700 cm-1 (the latter feature was impaired by the 720 cm-1 band of MoOF4) [3]. The following assignments of frequencies (in cm-1) to vibrations of MoFs moleeules have been given assuming D3h symmetry [4]: frequency ...... 747 703 685 510 730 250 203 440 vibration ...... v, For (estimated) fundamental frequencies see also p. 98. Matrix Isolated MoF5• The IR spectrum of matrix isolated MoFs was studied at 20 K (MoFs :Ar= 1 :500 to 1: 1000). The MoFs pressure was varied by changing the temperature of the solid MoFs stock between room temperature and 50°C. The vaporized MoFs was equilibrated in aseparate chamber between room temperature and 150°C. Thus, saturated and unsaturated vapors were produced containing monomeric and oligomeric species in varying proportions. The matrix isolated MoFs monomers show the following IR features in the v = 100 to 800 cm-1 range (assignments assuming D3h symmetry) [1]: 112 261 713 assignment ...... v7(E') vs(E') vs(E') IR features from matrix isolated MoFs at 20 K attributed to polymerie species occur at 231, 704,716, and 768 cm-1 [1]. Matrix isolated MoFs (MoFs:Ar=1:500) was UV irradiated (1.~200 nm) and studied by IR spectroscopy at 6 ± 1 K. Bands appearing at 693.5 and 658 cm-1 after the photolysis are attributed to vibrational modes of MoFs. The intensity ratio of the 658 to 693.5 cm-1 lines is 1 :3.8. Comparison with matrix isolated UFs suggests that MoFs is a tetragonal pyramidal moleeule (C 4V symmetry) [2]. References: [1] Acquista, N.; Abramowitz, S. (J. Chem. Phys. 58 [1973].5484/8). [2] Blinova, O. V.; Predtechenskii, Yu. B. (Opt. Spektroskopiya 47 [1979] 1120/5; Opt. Spectrosc. [USSR] 47 [1979] 622/4). [3] Grimm, F. A.; Weaver, C. F. (ORNL-4449 [1970]121). [4] Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A. (J. Chem. Soc. A 1969 2351/4). [5] Paine, R. T.; Asprey, L. ~. (Inorg. Chem. 13 [1974]1529/31). [6] Bates, J. B. (Spectrochim. Acta A 27 [1971]1255/8). [7] Bates, J. B. (Inorg. Nucl. Chem. Letters 7 [1971] 957/60). [8] Khaldoyanidi, K. A.; Ikorskii, V. N.; Gramkina, Z. A. (Zh. Strukt. Khim. 17 [1976] 364/6; J. Struct. Chem. [USSR]17 [1976] 315/7). 2.2.7.7 Chemical Reactions On Heating. At 150°C the liquid compound begins to disproportionate to gaseous MoFs and a solid phase wh ich is believed to be MoF4 • This process is catalyzed by borosilicate glass at lower temperatures so that the MO!",s(l) changes color from yellow to green after a few hours in the glass apparatus [1]. The temperature of beginning disproportionation was also found to be 165°C [2]. The equilibrium constant Kp (in Pa) for the reaction 2 MoFs(l) ~ MoFs(g) + MoF4(dis solved in MoFs) was determined as 1.24 ± 0.2 and 2.92 ± 004 at 373.0 and 392.5 K, respectively Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 113 [3,41]. These data [3, 41] indicate that for Liquid MoFs with an excess of MoF4 over MoF6, the relationship between the partial pressure of MoF6, P(6)' (in atm) and the moLe fraction of MoF4 in the soLution, x4 , is given by Ln{p(6)' x4) = 5.827 -6400fT (± 0.03) for T = 340 to 540 [42]. When MoFs is sLowLy heated to 200°C under refLuxing conditions whiLe maintaining the pressure in the 10-3 Torr range, pure MoF4 is obtained as the solid residue [4]. However, formation of soLid MoF3 is observed when MoFs is heated in a vacuum at 200°C and the voLatiLe MoF6 is removed by pumping [5]. At higher temperatures, e.g. 250°C, in vacuum the formation of MoF3 is known to be due to the thermaL disproportionation of MoF4 [4]. For the gas phase equiLibrium 2MoFs~MoF4 + MoFs see the mass spectrometric study of the thermaL decomposition of MoF4 at ~550°C [18], see aLso p.91. For the bond dissociation energy D298{F4Mo-F), 88 kcaVmoL are given [6,7]; D{F4Mo-F)/R =44000 K [8]. In a Literature review on thermochemical data, the heat of dissociation of gaseous MoFs was estimated to be 591 kcaVmol [9]. The minimum that occurs at the bond number n=5 in the 0 vs. n relationship for the series MoFn is discussed in [10]. With Electrons. ELectron impact with 60 eV eLectrons at 296.4 K on the neutraL species sampLed from the saturated vapor over crystaLLine (cl and supercooled Liquid (s) MoFs produces monomer and oLigomer positive ions with the foLLowing reLative abundances: ion .... ~ ...... MoFt MoF! MoF~ M02Fio M02F~ M02F~ MoFs{c) ...... 2 100 21 0.1 110 2.5 MoFs{s) ...... 8.3 360 0.58 450 ion ...... ~ ...... M03Fis M03Fi4 M03Fi3 M04Fto M04Fi9 M04Fia MoFs{c) ...... 6 17 0.5 0.07 0.4 0.01 MoFs{s) ...... 25 86 2.7 The character of the processes, invoLving the fragmentation of the metastabLe ions was studied. A Large roLe is pLayed by processes in which not onLy the peripheraL fLuorine atoms but aLso poLyatomic fragments that incLude metaL atoms are spLit out. The appearance potentiaLs of the M03Fis and M04Fto ions (11.4 ± 0.2 and 11.6 ± 0.2 eV, respectiveLy) give evidence that these ions are "moLecuLar ions" whiLe the remaining ions are fragment ions. Contributions of the trimer (3), tetramer (4), and pentamer (5) precursor moLecuLes of the gas phase to the intensities of the ions are [11, 12]: ion ...... MoFt MoF! M02Fio M02F~ precursor moLecuLe 3 4 3 4 3 4 3 4 contribution in % ...... 95 5 97 3 92 8 94 6 ion ...... M03Fis M03Fi4 M04F~o M04Fi9 precursor moLecuLe 3 4 3 4 4 5 4 5 contribution in % ...... 100 0 47 53 100 0 59 41 For the MoFs+e-~MoFt+2 e- reaction, the threshoLd is 10.7±0.3eV [8]. With 70eV eLectrons at room temperature aLso MoF+ and MoF~have been detected [13 to 17]. The reLative abundances of monomer positive ions produced in the vapor phase over MoFs at 25°C are MoFt (20), MoF! (100), MoF~ (47), MoF~ (24), MoF+ (10) [14]. ComparabLe data are reported in [13,15]. The reLative abundances of oLigomer ions.at 48°C and 70 eV are monomer (100), dimer (20), trimer (1.3), tetramer (0.04) [17]. lonization efficiency curves for MoFs fragments are plotted for eLectron energies ranging from 15 to 45 eV [18]. With ELements. MoFs remains unaffected by air dri.ed with P20 S [19], see aLso [20]. PartiaL oxidation after exposure to air for 30 min was mass spectrometricaLLy detected [13]. Gmelin Handbook Mo Suppl. Vol. B 5 8 114 Mo~bdenum Ruorides In a stream of F2 the hexafluoride forms [21]. For the reaction MoFs(s) + F-(g) ~ MoFa(g) the fluoride ion affinity ßH F = -412±6 kJ/mol has been estimated using the heats of alkali ne hypochlorite hydrolysis of the alkali metal hexafluoromolybdates(V) [22]. ßHF = -413.4±20.1 kJ/mol for the fluoride ion affinity of gaseous MoFs has been determined from equilibrium data of the gas-phase reaction MoFs + 2 BeF3~ MoFa + BeF; at 840 to 940 K and the known heat of loss of F- for BeF3 [23]. With Si powder in an autoclave at temperatures between 140 and 220°C, MoFs is reduced to give MoF4 and SiF4 [24]. For the reaction with Si in anhydrous HF see p. 117. Upon heating MoFs with Mo at 200 to 210°C in vacuum MoF4 forms [25], at 400°C MoF3 is obtained [19]. MoFs appears to be quite stable in a dry, stainless steel vessel [20]. With Inorganic Compounds. MoFs reacts vigorously with moisture [1,14,20] forming blue hydrolytic products [19]. This process proceeds so readily that green or blue colorations of the sam pie prove to be valuable signs for the presence of traces of H20 [3]. With liquid H20, colored solutions form [26]. With water vapor at p(H20) = 18 Torr at room temperature an increase in mass indicates the formation of a hydrate, MoFs·5.5H20, which upon subsequent evacuation to 10-3 Torr transforms to MoOF3 ·0.5H20 (see p. 192) [27]. The treatment of MoFs with oxygen and water vapor at 100 to 180°C yields a material with a cubic Re03 structure, probably an oxide fluoride [19]. At - 78°C the reaction with excess liquid NH3 gives red-brown MoFs ·1.5 NH3 which at - 70 to - 65°C becomes solvated to the dark brown insoluble powdery MoFs·5NH3. One mole NH 3 is easily removed from the laUer compound in vacuum at room temerature [28]. At - 55 and -35°C MoFs·4NH3 is the only reaction product [28,29]. The reaction with liquid NH3 is accompanied by two exothermic effects at -74 and - 49°C [28]. A red-brown MoFs: NH3 = 1 :1 adduct was found in [30]. With excess gaseous NOF at 25°C (16 h) solid NOMoFs forms [31]. The reaction of MoFs with CIOF3 produces both MoFs and MoOF4 and subsequently adducts of the latter, e.g. [CIOF2]+[MoOFs]- and [CIOF2]+[M020 2Fg]- [32]. Thermographic investigations of the interaction of MoFs with alkali metal fluorides in sealed evacuated quartz ampules show the presence of a powerful exothermic effect close to the melting point of MoFs (45°C) in the case of KF, NH 4F, RbF, and CsF. With NaF, an exothermic effect occurs only at 200°C. Complexes of the type MIMoFs are obtained with MI = K, Rb, and Cs. The NH 4 complex is subjected to further autoreduction, while the yield of the sodium salt is small and the product contains substantial admixtures of the initial NaF [33], cf. also [34]. At 130 to 150°C, the temperature of beginning thermal disproportionation of MoFs, virtually no reaction occurs between gaseous MoFs and solid alkali fluorides [33]. From mass spectrometric equilibrium data at 840 to 940 K in the vapor generated by reacting MoF3 with KBe2FS' ßH~298 = - 20.25 ± 5.86 kJ/mol for the reaction MoFs + BeF3~ MoFa + BeF2 was calculated [23]. For the effect of borosilicate glass on liquid MoFs see p. 112. With SbF3 in a stream of argon at 150 to 200°C, MoFs is reduced to MoF3 [19]. When VFs is distilled onto excess MoFs at -196°C and the system is warmed to room temperature, MoFs and VF4 form [35]. With Mo03 at 180°C, MoOF3 is the main reaction product, also some MoOF4 forms in a side reaction [36]. The formation of MoOF3 wh ich was observed when a mixture of MoFs and MoOF4 was heated to 200°C, is attributed to the reaction MoF 4 + MoOF 4 ~ MoFs + MoOF3 the MoF 4 being formed (together with MoFs) by disproportionation of MoFs at 165°C [37]. The fusion diagram of the MoFs-MoCls system shows the formation of one incongruent melting com- Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 115 pound, MoFCI4 , and three congruently melting compounds of compositions MoF4CI, MoF3CI2, and MoF2Cl3 [38]. For details see the MoCls-MoFs system in "Molybdenum" Suppl. Vol. B 6 (to be published). MoFs reduces UFs to UFs [39]. With Organic Compounds. With excess acetonitrile, pyridine, dimethylether, or dimethyl sulfide at room temperature reactions occur and addition compounds of the compositions MoFs·2CH3CN, MoFs' 2CsHsN, MoFs' CH 30CH3, and MoFs' CH 3SCH 3 are obtained [30]. Mixing MoFs and CH 3CN or CH 2ClCN at temperatures below 20°C followed by removal of excess ligand, forms complexes of composition MoFs' NCCH3 (with emphasis on being distinct from the bis compound above) and MoFs' NCCH 2CI, respectively [40]. References: [1] Edwards, A. J.; Peacock, R. D.; SmalI, R. W. H. (J. Chem. Soc. 19624486/91,4486/7). [2] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568/74). [3] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977]1149/63,1151,1161). [4] Weaver, C. F.; Friedman, H. A. (ORNL-4449 [1970]113/5). [5] Weaver, C. F.; Friedman, H. A. (ORNL-4191 [1967] 142/3). [6] Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63). [7] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [8] Kleinschmidt, P. D.; Lau, K. H.; Hildenbrand, D. L. (J. Chem. Thermodyn.11 [1979]765/72). [9] Feber, R. C. (LA-3164 [1964]1/187, 178; C.A. 63 [1965] 9124). [10] Pervov, V. S.; Fal'kengof, A. T.; Murav'ev, E. N. (Koord. Khim. 4 [1978]1828/34; Soviet J. Coord. Chem. 4 [1978] 1400/5). [11] Gotkis, I. S.; Gusarov, A. V.; Pervov, V. S.; Butskii, V. D. (Koord. Khim. 4 [1978] 720/4; Soviet J. Coord. Chem. 4 [1978] 536/40). [12] Gotkis, I. S.; Gusarov, A. V.; Pervov, V. S.; Butskii, V. D. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 92; C.A. 90 [1979] No. 29931). [13] Redman, J. D.; Strehlow, R. A. (ORNL-4229 [1968] 37/9; N.SA 22 [1968] No. 25374). [14] Paine, R. T.; Asprey, L. B. (lnorg. Chem. 13 [1974]1529/31). [15] Strehlow, R. A.; Redman, J. D. (ORNL-4254 [1968]134/6). [16] Vasile, M. J.; Jones, G. R.; Falconer, W. E. (Intern. J. Mass Spectrom. Ion Phys. 10 [1972/73] 457/69, 462). [17] Falconer, W. E.; Jones, G. R.; Sunder, W. A.; Vasile, M. J.; Muenter, A. A.; Dyke, T. R.; Klemperer, W. (J. Fluorine Chem. 4 [1974] 213/34, 220, 226/7). [18] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970] 116/21, 118). [19] LaValle, D. E.; Steele, R. M.; Wilkinson, M. K.; YakeI, H. L., Jr. (J. Am. Chem. Soc. 82 [1960] 2433/4). [20] Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A.; Steven, A. M. (lnorg. Syn.13 [1971]146/50). [21] Brooksbank, W. A.; Carter, R. J.; Osborne, M. F. (CF-58-6-86 [1958]1/22, 16; N.SA 12 [1958] No. 13008; ORNL-2614 [1958]148/50; N.SA 13 [1959] No. 2275). [22] Burgess, J.; Haigh, 1.; Peacock, R. D.; Taylor, P. (J. Chem. Soc. Dalton Trans. 19741064/6). [23] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982]145/56, 150). [24] Couturier, J.-C.; Angenault, J.; Mary, Y.; Quarton, M. (J. Less-Common Metals 138 [1988] 71/7, 72). [25] Opalovskii, A. A.; Fedorov, V. E.; Khaldoyanidi, K. A. (U.S.S.R. 265879 [1968/72]; C.A. 78 [1973] No. 6040). [26] Peacock, R. D. (Proc. Chem. Soc. 1957 59). GmeLin Handbook Mo Suppl. Vol. B S 8" 116 Molybdenum Fluorides [27] Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981]573/6; Russ. J.lnorg. Chem. 26 [1981] 310/2). [28] Belyaev, I. N.; Blokhina, G. E.; Opalovskii, A A. (Zh. Neorgan. Khim. 17 [1972] 2465/7; Russ. J. Inorg. Chem. 17 {1972] 1288/90). [29] Opalovskii, A. A.; Blokhina, G. E. (Izv. Vysshikh Uehebn. Zavedenii Khim. Khim. Tekhnol. 15 [1972]1617/9; C.A 78 [1973] No. 66436). [30] Mereer, M.; Ouellette, T. J.; Rateliffe, C. T.; Sharp, D. W. A. (J. Chem. Soe. A 1969 2532/4). [31] Geiehman, J. R.; Smith, E. A; Trond, S. S.; Ogle, P. R. (Inorg. Chem. 1 [1962] 661/5). [32] Bougon, R.; Bui Huy, T.; Charpin, P. (Inorg. Chem. 14 [1975]1822/30, 1829). [33] Opalovskii, A A.; Khaldoyanidi, K. A. (Izv. Akad. Nauk SSSR Sero Khim. 1973279/82; Bull. Aead. Sei. USSR Div. Chem. Sei. 1973 270/2). [34] Nikolaev, A V.; Opalovsky, A. A; Fedorov, V. E. (Therm. Anal. Proe. 2nd Intern. Conf., Woreester, Mass., 1968 [1969], Vol. 2, pp. 793/810,799/800; C.A. 73 [1970] No. 94206). [35] Canterford, J. H.; O'Donnell, T. A (Inorg. Chem. 6 [1967] 541/4). [36] Blokhina, G. E.; Belyaev, I. N.; Opalovskii, A A; Belan, L. I. (Zh. Neorgan. Khim. 17 [1972] 2140/3; Russ. J.lnorg. Chem. 17 [1972]1113/5). [37] Opalovskii, A A.; Anufrienko, V. F.; Khaldoyanidi, K. A (Dokl. Akad. Nauk SSSR 184 [1969] 860/2; Dokl. Chem. Proe. Aead. Sei. USSR 184/189 [1969] 97/9). [38] Khaldoyanidi, K. A.; Yakovlev, I. I. (Zh. Neorgan. Khim. 32 [1987]1089/91; Russ. J. Inorg. Chem. 32 [1987] 610/2). [39] Galkin, N. P.; Tumanov, YU. N.; Butylkin, YU. P. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 2, pp. 12/21, 18; C.A 69 [1968] No. 110616). [40] Fuggle, J. C.; Sharp, D. W. A.; Winfield, J. M. (J. Fluorine Chem. 1 [1971/72] 427/31). [41] Krause, R. F., Jr. (Proe. Eleetroehem. Soe. 78·1 [1978]199/209). [42] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spee. Issue No. 7 [1980]195/356,244). 2.2.7.8 Solubility. Solutions Solubility. MoF5 is soluble in anhydrous HF without deeomposition [1]. The eonduetivity and the Raman speetrum of MoF5 in anhydrous HF indieate that the dissolved eompound is essentially nonionized [2]. For ealeulations of solution enthalpies of MoF5 (s) in aqueous HF eontaining Xe03 see [3]. On dissolving MoF5 in liquid S02 a yellow-orange solution forms [4]. MoF5 is insoluble in most organie solvents but dissolves in aeetonitrile and dimethyl ether giving yellow solutions from whieh addition eomplexes were obtained (see p. 115) [5]. Liquid MoF5 forms with hexaehloro-1,3-butadiene a system of two liquids with limited miseibility having a eonsolute temperature of 105.3°C and a eonsolute eoneentration eorre sponding to a 0.635 mole fraetion [6]. Properties of Solutions in HF. The Raman speetrum of the solution of MoF5 in anhydrous HF (saturated at 25°C) shows a strong, polarized band at 746 em-1 . The eleetrieal eonduetivity was studied with the anhydrous HF solution at O°C. The 0.087M solution (not saturated) has a speeifie eonduetivity of 1.25 x 1O-4 Q-1. em-1 when eorreeted for that of the solvent (4.28 x 10-5 Q-1. em-1). The equivalent eonduetivity f.I = 0.15 Q-1. em-1 . mol-1 and the degree of ionization a=0.04% [2]. Gmelin Handbook Mo Suppl. Vol. B 5 117 Reactions in Solutions. In anhydrous HF (10 mL) at room temperature, MoF5 (5.23 mmol) reacts with Si powder (1.2 mmol) to give MoF4 and volatile Si compounds [1]. On dissolving crystalline MoF5 in aqueous NaOH (1 M or 0.1 M; 120 mL) containing NaOCI (10 to 12%; 30 mL), MoF5 is oxidized and hydrolyzed according to 2 MoF5 + 140H-+ CIO--+ 2 MoO~- + 10 F- + CI- + 7 H20. The enthalpy of this reaction was experimentally determined as ßH, "" 692(6) kJ/mol [7]. Formation of complex fluoro anions in the reactions of MoF5 with various fluorides in S02' S02FCI, CFCI3, and CH 2CI2 solutions has been studied by 19F NMR, IR spectroscopy, and X-ray powder diffraction. There are rapid reactions with the solvents in the presence of AsF5 (except CFCI3 as solvent), SbF5, NbF5, or TaF5 to give complex mixtures, whereas BF3 and PF5 are unreactive in all the solvents investigated. Equimolar amounts of MoF5 and (TBA)NbFs (TBA"" tetra-n-butyl ammonium) in CH2CI2 react to form the anions MoNbF11 and Nb2F11 ; with AgTaFs the Ta2F11 ion forms. Formation of complex fluoro anions is also observed in the reaction between MoF5 and AgBF4 in CH 2CI2 solution but not with PF6", AsFs, and SbF6"with Ag+ or TBA+ cations [4]. References: [1] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [2] Paine, R. T.; Quarterman, L. A. (J. Inorg. Nucl. Chem. H. H. Hyman Mem. Vol. 197685/6). [3] Douglas, T. B.; Beckett, C. W. (AD-782 028-5 GA [1974]1/123, 83; C.A. 83 [1975] No. 16681). [4] Brownstein, S. (Can. J. Chem. 51 [1973] 2530/3). [5] Ouellette, T.J.; Ratcliffe, C. T.; Sharp, D. W. A.; Steven,A. M. (Inorg. Syn.13 [1971]146/50). [6] Galkin, N. P.; Bertina, L. E.; Orekhov, V. T.; Paklenkov, E. A. (Zh. Fiz. Khim. 49 [1975]2454; Russ. J. Phys. Chem. 49 [1975]1443). [7] Burgess, J.; Haigh, 1.; Peacock, R. D. (J. Chem. Soc. Dalton Trans. 1974 1062/4). 2.2.8 Molybdenum(V1) Fluoride MoFs Older data are given in "Molybdän", 1935, pp. 150/1. Survey. Molybdenum hexafluoride occurs in the Mo--F system, see p. 67. It is usuallY prepared by the fluorination of metallic molybdenum preferably with elemental fluorine. At room temperature the compound exists as a colorless liquid which on cooling below about 17SC turns to a white "plastic" crystal mOdification of cubic symmetry. A modification of orthorhombic symmetry exists below about -9.8°C. In its chemical behavior MoFs shows more resemblance to UF6 than to WFs. It is a mild fluorination reagent but only a very weak oxidant. Because of its extreme sensitivity to moisture, special precautions for handling and storage are necessary. MoFs was denoted as a toxic substance [1,2], but later only a low toxicity was stated [3]. References: [1] Ouellette, T.J.; Ratcliffe, C. T.; Sharp, D. W. A.; Steven, A. M. (Inorg. Syn.13 [1971]146/50). [2] Paine, R. T.; Asprey, L. B.; Graham, L.; Bartlett, N. (Inorg. Syn. 19 [1979] 137/40). [3] Shustov, L. D.; Nikolenko, L. N.; Senchenkova, T. M. (Zh. Obshch. Khim. 53 [1983]103/5; J. Gen. Chem. [USSR] 53 [1983] 85/6). Gmelin Handbook Mo Suppl. Vol. B 5 118 MoLybdenum Fluorides 2.2.8.1 Preparation. Formation. Purification Preparation by Fluorination of Metallic Molybdenum. The direct combination of the eLements using either fLow or static techniques is the most common method to produce moLybdenum hexafluoride. The moLybdenum metaL is used as a fineLy divided powder and is pretreated at 900 or 1000°C with hydrogen to reduce any oxide coating [1 to 4). When the moLybdenum powder is previousLy mixed with magnesium fluoride in the moLe ratio 2:1, the fLuorination is more compLete and uniform (4). The fLuorine used can be diLuted with oxygen-free nitrogen (5). The fLuorination temperature of 60°C, which was appLied in the first preparations (see "MoLybdän", 1935, p. 150), is too Low to obtain a compLeteLy fLuorinated materiaL in good yieLd (6). Therefore, higher temperatures are proposed in the Later papers, e. g., initiation of the reaction at 100°C (1), fLuorination at 150 to 200 (7),300 to 350 (8), or 400°C (2). MoLybdenum metaL is heated to 315°C and fLuorinated with F2 at apressure of about 260 Torr (5 Lb/in 2). As soon as F2 enters the reaction tube the temperature rises to 480°C (yieLd: 78%) [6, 9). Preparation can aLso be accompLished under pressure (10). The MoFs separates as a white soLid in a trap cooLed by dry ice + trichLoroethyLene (6) or Liquid air (10). Excess fLuorine is pumped off (10) and MoFs purified as described beLow. The fLuorination vesseL can consist of copper [1,5,11 J, which proved to be a better materiaL than pLatinum (12). A speciaL nickeL tube is used in [6, 9). For a quartz reactor see (15). GLass was found to be a suitabLe materiaL for the traps when powdered NaF was used as a getter to remove HF (1), thus preventing hydrolysis reactions invoLving Si02 (cf. p. 163). See aLso (7). The probLems invoLved in the technicaL production of metaL hexafluorides (e.g. MoFs) from the eLements, especiaLLy impurities in the fLuorine gas, the high temperatures required for fLuorination, and the Large exothermic effects of fLuorination, are discussed in (13). NitrosyL fluoride hydrogen fluoride, NOF·3 HF, is a very good fLuorinating agent to produce MoFs from moLybdenum foLLowing the equation Mo+6NOF·3HF~MoFs+6NO+18HF. The reaction is carried out at 40 to 65°C (-1 h) at a moLe ratio of 6.01 to 6.8NOF·3HF per Mo. A mixture of soLid MoFs and Liquid HF is separated in a cooLed receiver (dry ice + acetone). The HF is decanted and the crude MoFs is heated to 20 to 25°C at which temperature mostof the remaining HF is removed (14). The fLuorination of moLybdenum with gaseous CLF3 produces MoFs in a spontaneous reaction, the metaL burning with bright fLashes and evoLution of heat. The apparatus consists of a quartz reaction tube with an Ni boat for the moLybdenum and quartz trap (with NaF) and condenser which are cooLed with Liquid nitrogen or dry ice for the separation of MoFs. For uniform fLuorination and distiLLation of the fluoride the reactor is heated with a burner. Because the MoFs formed is contaminated with some CLF3 it is used in further fLuorinations. After a third passage through fresh metaL the CLF3 content is -0.2% which is washed out with Liquid HF at dry ice temperature [15, 16). ALso moLybdenum suspended in Liquid HF can be fLuorinated by CLF3 to give a coLorLess soLution, wh ich at high concentration precipitates MoFs as a white soLid (17). In contrast to CLF3 the chLorine monofluoride, CLF, reacts smoothLy with moLybdenum over a wide temperature range to give MoFs and CL2. CLF is readiLy utiLized in the gaseous state without diLution or process controL. The MoFs synthesis is carried out under substantiaLLy anhydrous conditions at atmospheric pressure. After reaction the reaction cylinder is cooLed to -78°C and the CL2 is removed by pumping for several hours at this temperature (18). With bromine trifluoride, BrF3, as the fLuorinating agent molybdenum powder reacts in a closed system. The resuLting voLatiLe products are passed through a trap at -23°C to remove excess BrF3 and then condensed at -196°C. The MoFs produced bythis method is contaminat ed with bromine (19). It was found that BrF3 attacks the moLybdenum with incandescence [52). Gmelin Handbook Mo Suppl. Vol. B 5 MoFa 119 High yields of MoFa can be obtained by the electric explosion of molybdenum metal in SFa. The metal is in the form of a wire of 20 to 30 mil diameter (0.51 to 0.76 mm). The metal explosion is created by instantaneous discharge of electric charges stored at high potentials. With 430 mg Mo and a mole ratio SFa:Mo of 4.0 and an input energy of 2190 J, 79 to 84% of the metal is converted to MoFa. In addition to MoFa sm all amounts of nonvolatile compounds (MoF3 ?) form as a thin film on the reactor wall. The only volatile by-product, SF4, can be efficiently separated by distillation, as can be unreacted SFa. The great efficacy of SFa as a fluorinating agent in this process is fortunate because of its inertness at ordinary conditions and thus ideal handling properties [51]. Preparation by Fluorination of Oxygen-Containing Molybdenum Compounds. By fluorination of Mo03 with F2 the hexafluoride is obtained (togetherwith oxide fluorides) if the F2 concentra tion is high and the reaction time is long enough [20]. Other oxygen-containing molybdenum compounds can be fluorinated with elemental fluorine at temperatures above 250°C. Then the reaction gases are contacted with NaF at 200 to 500°C prior to separation of the final fluorination products [21]. MoFa can also be produced by reacting Mo03 with BrF3 or IFs [22], however, the separation of MoFa and bromine is hindered by the solubility of the element in the fluoride [53]. Fluorinations with SF4 are conducted in flow systems at atmospheric pressure or in pressure vessels. The bomb is charged with the oxide, flushed with nitrogen, cooled to -78°C, and evacuated to 1 Torr. SF4 in excess is distilled into the bomb which is then heated to 70 to 350°C (9 h) [23, 24]. Preparation of Radioactive Molybdenum Hexafluoride. Radioactive 99MoFa can be obtained by fluorination of very pure 99Mo (preactivated with thermal neutrons) with F2 at 400°C [25], see also [26, 27]. As an alternative MoFs is irradiated in a reactor to obtain 99MoFs which is then treated with flowing fluorine at 100°C [26, 27]. Formation Reactions. For formation of MoFa by thermal disproportionation of MoF4 and MoFs see pp. 91 and 112, respectively. The hexafluoride forms by the anodic oxidation of molybdenum in anhydrous HF [28], by fluorination of the metal with NF3 [29, 30], and by reacting Mo with KN03 in anhydrous HF (also gives MoOF4) [31]. The reactions of NF3 with Mo03 at 430°C and with MoN at 260°C yield MoFa together with other compounds [29]. MoFs is partly converted to MoFa by ClOF3 [32]. With VFs at room temperature MoFs (in excess) gives MoFa and VF4 [33]. MoOF4 is quantitatively transformed into MoFa by ClF3 after a contact time of a few months [32]. M02Cl3 Fa decomposes to MoFa and MoCl3 at >80°C [34]. MoFa and Mo form by the reaction of MoBr2 and HF (wh ich starts at 700°C) above 800°C as weil as by the reaction of MoBr2 with BrF3 [52]. MoS2 can be fluorinated to MoFa by F2 [35], NF3 [29], and CIF [18]. Mo(CO)a reacts with F2 above 50°C [36] and with excess IFs in the cold to give MoFa [37]. Mo(CO)4F2 is oxidized by XeF2 to give MoFa [38]. Decomposition of Li2MoFa, Na2MoFa, and NaMoF7 with formation of MoFa was observed at temperatures above 200°C [7], see also [39]. Purification. MoFa can be freed from most of its impurities by successive vacuum distilla tions into receiving traps (trap-to-trap distillation) at low temperatures, see e. g. [40 to 44]. The removal of HF, wh ich requires considerable care, especially when the compound is handled in glass systems (see p. 163), is accomplished by sorption on granulated NaF getter usually added to the solid crude MoFa before distillation, see e.g. [7,45 to 49]. The purification can be carried out in a system of several traps in series connected to a high-vacuum system. These GmeLin Handbook Mo Suppl. Vol. B 5 120 MoLybdenurn FLuorides traps are fLarned in vacuurn and gettered with NaF before use. The first of the cLean traps is then cooLed to -78°C and the Last to -196°C. The crude MoF6 bLended with NaF is distiLLed at roorn ternperature, aLrnost aLL of the MoF6 being deposited as coLorLess crystaLs in the trap at -78°C. SrnaLL arnounts of SiF4 condense in the trap at -196°C whiLe the NaF getter and rnoLybdenurn oxide fluorides rernain in the originaL trap [1]. An aLternative route invoLves repeated evaporations of the hexafluoride into an expansion charnber foLLowed by condensa tion into a buLb containing NaF and purnping out the residuaL gases. The MoF6 is condensed by cooLing with dry ice+acetone rnixture untiL the pressure in the,charnber is constant and approxirnateLy equaL to the estirnated vapor pressure [50]. A detaiLed description of an apparatus and the purification procedure is aLso given in [45]; see aLso [15, 16]. MateriaLs suitabLe for purification equiprnent are gLass [1,45], rnoneL and stainLess steeL [44], rnoneL and nickeL [2], nickeL and copper [54], nickeL [55], and copper [1, 5]. References: [1] O'DonneLL, T. A. (J. Chern. Soc. 19564681/2). [2] OSborne, D. W.; Schreiner, F.; Malrn, J. G.; Selig, H.; Rochester, L. (J. Chern. Phys. 44 [1966] 2802/9, 2802). [3] Burns, R. C.; O'DonneLL, T. A.; Waugh, A. B. (J. FLuorine Chern. 12 [1978]505/17, 507). [4] KhaLdoyanidi, K. A.; YakovLev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khirn. 26 [1981] 3067/9; Russ. J. Inorg. Chern. 26 [1981]1639/40). [5] Cady, G. H.; Hargreaves, G. B. (J. Chern. Soc. 1961 1563/8, 1565). [6] Bernhardt, H. A; Bishop, H. W.; Brusie, J. P. (TID-5212 [1955)153/4; C.A. 1956 16499). [7] Peka, 1.; Sykora, F.; Vachuska, J. (CoLLection Czech. Chern. Cornrnun. 34 [1969]2857/64, 2858). [8] GaLkin, N. P.; Bogdanov, G. V.; Fedorov, V. D.; Orekhov, V. T. (Zh. Neorgan. Khirn. 16 [1971] 496/9; Russ. J. Inorg. Chern. 16 [1971] 262/4). [9] Trevorrow, L. (ANL-RCV-SL-1094 [1956]1/6; N.S.A 11 [1957] No. 11596). [10] HeLLberg, K. H.; MüLLer, A.; GLernser, O. (Z. Naturforsch. 21 b [1966) 118/21). [11] O'DonneLL, T. A.; Stewart, D. F. (J. Inorg. NucL. Chern. 24 [1962] 309/14, 310). [12] HenkeL, P.; KLe rn rn , W. (Z. Anorg. AlLgern. Chern. 222 [1935] 70/2). [13] Rakov, E. G.; DzhaLavyan, A V.; Dudin, A S. (Tr. Inst. Mosk. Khirn. TekhnoL. Inst. No. 125 [1982] 82/7; C.A 100 [1984] No. 166924). [14] ALLied ChernicaL Corp. (Neth. AppL. 6400628 [1964]; C.A. 62 [1965] 3690). [15] NikoLaev, N. S.; BusLaev, Yu. A.; OpaLovskii, A. A. (Zh. Neorgan. Khirn. 3 [1958]1731/3; Russ. J. Inorg. Chern. 3 No. 8 [1958] 14/7). [16] NikoLaev, N. S.; OpaLovskii, A. A. (Zh. Neorgan. Khirn. 4 [1959] 1174/83; Russ. J. Inorg. Chern. 4 [1959] 532/6). [17] CLifford, A F.; BeacheLL, H. C.; Jack, W. M. (J. Inorg. Nucl. Chern. 5 [1957] 57/70, 65). [18] Pitts, J. J.; Jache, A. W.; OLin Mathieson ChernicaL Corp. (U.S. 3373000 [1966/68]; C.A. 68 [1968] No. 88678; Inorg. Chern. 7 [1968]1661/3). [19] Cox, B.; Sharp, D. W. A; Sharpe, A. G. (J. Chern. Soc. 1956 1242/4). [20] Rakov, E. G.; Marinina, L. K.; Sudarikov, B. N.; Koshechko, L. G.; Fedorov, G. G. (Tr. Mosk. Khirn. Tekhnol. Inst. No. 65 [1970] 28/30; C.A. 76 [1972] No. 104691). [21] Grornov, B. V.; Koshechko, L. G.; Rakov, E. G.; Sudarikov, B. N. (U.S.S.R. 416319 [1972/74] frorn C.A. 81 [1974] No. 108002). [22] NikoLaev, N. S.; Sukhoverkhov, V. F. (BuL. Inst. PoLiteh. lasi [2)3 No. 1/2 [1957]61/6, 65; C.A. 19599871). Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 121 [23] Oppegard, A. L.; Srnith, W. C.; Muetterties, E. L.; Engelhardt, V. A. (J. Am. Chern. Soc. 82 [1960] 3835/8). [24] Srnith, W. C.; E.I. du Pont de Nernours & Co. (U.S. 2904398 [1957/59]; C.A. 19603883/4). [25] Prusakov, V. N.; Ezhov, V. K.; Efrernov, E. A. (At. Energiya SSSR 41 No. 2 [1976]98/101; C.A. 85 [1976] No. 149749). [26] Brooksbank, W. A., Jr.; Carter, R. J.; Osborne, M. F. (CF-58-6-86 [1958]1/22, 14, 16; N.S.A. 12 [1958] No. 13008). [27] Brooksbank, W. A., Jr.; Carter, R. J.; Osborne, M. F. (ORNL-2614 [1958]148/50; N.S.A. 13 [1959] No. 2275). [28] Hackerman, N.; Snavely, E. S.; Fiel, L. D. (Corrosion Sci. 7 [1967] 39/50, 41, 43). [29] Glernser, 0.; Wegener, J.; Mews, R. (Chern. Ber. 100 [1967] 2474/83, 2476, 2478/80). [30] Pervov, V. S.; Butskii, V. D.; Podzolko, L. G. (Zh. Neorgan. Khirn. 23 [1978]1486/91; Russ. J. Inorg. Chern. 23 [1978] 819/22). [31] Wiechert, K. (Z. Anorg. Allgern. Chern. 261 [1950] 310/23, 322). [32] Bougon, R.; Bui Huy, T.; Charpin, P. (Inorg. Chern. 14 [1975]1822/30, 1829). [33] Canterford, J. H.; O'Donnell, T. A. (Inorg. Chern. 6 [1967] 541/4). [34] Stewart, D. F.; O'Donnell, T. A. (Nature 210 [1966] 836). [35] O'Hare, P. A. G.; Benn, E.; Yu Cheng, F.; Kuzrnycz, G. (J. Chern. Thermodyn. 2 [1970] 797/804). [36] Peacock, R. D. (Proc. Chern. Soc. 1957 59). [37] Hargreaves, G. B.; Peacock, R. D. (J. Chern. Soc. 19584390/3). [38] O'Do.nnell, T. A.; Phillips, K. A. (Inorg. Chern. 12 [1973]1437/8). [39] Kuhrt, W.; Kreutz, R.; Massonne, J. (Kerntechnik 13 [1971)17/20). [40] Hedge, W. D. (U.S. At. Energy Cornrn. K-1697 [1968]1/20; 7; C.A. 69 [1968] No. 70414). [41] McLean, R. R.; Sharp, D. W. A.; Winfield, J. M. (J. Chern. Soc. Dalton Trans. 1972676/8). [42] Paine, R. T.; Asprey, L. B. (Inorg. Chern. 13 [1974]1529/31). [43] Fukutorni, M.; Corbett, J. D. (J. Less-Cornrnon Metals 55 [1977] 125/30). [44] Nuttall, R. L.; Churnay, K. L.; Kilday, M. V. (J. Res. Nat!. Bur. Stand. 83 [1978]335/45,336). [45] Brady, A. P.; Clauss, J. K.; Myers, O. E. (WADC-TR-56-4 [1955]1/55, 32/5; N.SA 10 [1956] No. 7512). [46] Weaver, C. F.; Friedrnan, H. A.; Hess, D. N. (ORNL-4254 [1968] 129/34, 129). [47] Green, P. J.; Gard, G. L. (Inorg. Chern. 16 [1977]1243/5). [48) Krause, R. F., Jr.; Douglas, T. B. (J. Chern. Thermodyn. 9 [1977]1149/63,1151). [49] Krause, R. F., Jr. (Proc. Electrochern. Soc. 78-1 [1978] 199/209, 200). [50] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chern. Soc. 73 [1951]1164/7). [51] Johnson, R. L.; Siegel, B. (J. Inorg. Nucl. Chern. 31 [1969] 955/63, 957, 959). [52] Erneleus, H. J.; Gutmann, V. (J. Chern. Soc. 1949 2979/82). [53] ,Canterford, J. H.; Cotton, R. (Halides of the Second and Third Row Transition Metals, Wiley-Interscience, London 1968, p. 207). [54] Burke, T. G.; Srnith, D. F.; Nielsen, A. H. (J. Chern. Phys. 20 [1952] 447/54). [55] O'Donnell, T. A.; Stewart, D. F. (Inorg. Chern. 5 [1966] 1434/7). Gmelin Handbook Mo Suppl. Vol. 8 5 122 MoLybdenum Fluorides 2.2.8.2 The Moleeule 2.2.8.2.1 Point Group The point group was identified as eh' indicating a reguLar octahedran, fram anaLyses of the vibrationaL (both Raman and IR) spectra [1,2]; aLso see the Raman study [3] and the IR study [4]. The 0h symmetry of the moLecuLe is consistent with eLectron diffraction resuLts [5, 6] and aLso with the centrosymmetric structure deduced from the defLection behavior of moLecuLar beams in an eLectric quadrupoLe fieLd [7]. EarLy eLectron-diffraction studies [8, 9] were evaLu ated using reaL rather than compLex scattering factors. Therefore, these studies erroneousLy had pOinted to a rather distorted structure. The corrected theory [10, 11] removed the need for assuming point groups of Lower symmetry. The seeming discrepancy between diffraction and spectroscopic resuLts was discussed earLier in [12]. However, a smaLL deviation from 0h symmetry is required for the interpretation of vibronic features [13] observed in the photoeLec tron spectrum of MoF6 (see p. 124) [14]. Distorted MoF6 octahedra are estabLished for the orthorhombic solid by NMR (see p. 129) and neutron diffraction (see p. 132) techniques. References: [1] Burke, T. G.; Smith, D. F.; NieLsen, A. H. (J. Chem. Phys. 20 [1952] 447/54). [2] CLaassen, H. H.; Selig, H.; MaLm, J. G. (J. Chem. Phys. 36 [1962] 2888/90). [3] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951]1164/7). [4] Gaunt, J. (Trans. Faraday Soc. 49 [1953]1122/31). [5] Seip, H. M.; Seip, R. (Acta Chem. Scand. 20 [1966] 2698/710). [6] Seip, H. M. (SeLec. Top. Struct. Chem. 196725/68,59; C.A. 68 [1968] No. 117180). [7] Kaiser, E. W.; Muenter, J. S.; KLemperer, W.; FaLconer, W. E.; Sunder, W. A. (J. Chem. Phys. 53 [1970] 1411/2). [8] Braune, H.; Pinnow, P. (Z. Physik. Chem. B 35 [1937] 239/55, 244/5). [9] Bastiansen, 0. (Tidsskr. Kjemi Bergvesen Met. 11 [1951] 134). [10] GLauber, R.; Schomaker, V. (Phys. Rev. [2] 89 [1953] 667/71). [11] Schomaker, V.; GLauber, R. (Nature 170 [1952] 290/1). [12] Bauer, S. H. (J. Phys. Chem. 56 [1952] 343/51). [13] TopoL', I. A.; Dement'ev, A.I.; Rambidi, N. G.; Nefedov, V. I. (Koord. Khim. 5 [1979]860/5; Soviet J. Coord. Chem. 5 [1979] 676/80). [14] KarLsson, L.; Mattsson, L.; Jadrny, R.; Bergmark, T.; Siegbahn, K. (Phys. Scr. 14 [1976] 230/41). 2.2.8.2.2 Electronic Structure The caLcuLations of the eLectronic structure make use of SCF and SCC (seLf consistent fieLd and charge, respectiveLy), Xa (SLater exchange caLcuLation), SW (scattered wave), and DV (discrete variational) methods. To the eLectronic ground state lA1g [1], the foLLowing configuration of 36 vaLence eLectrons may be assigned: {4eg)4 {2t2g)6 {7a1g)2 {6t1u)2 {1t2u)6 {7t1u)6 {1t19)6. (The numbering of the moLecuLar orbitaLs takes aLL 96 eLectrons into account [2].) This configuration is in accordance with the sequence of LeveLs given in [3] from areanalysis of the photoeLectron spectrum [4] (see p. 124) and the UV absorption spectrum [5] (see p. 160) with the aid of theoreticaL caLcuLations of these spectra by an SCF-Xa-SW method [6]. The same sequence of LeveLs was obtained by another SCF-Xa-SW caLcuLation [7] (aLso see [8]), by SCF-Xa-DV caLcuLations [2], and by SCC Xa-DV caLcuLations [12]. Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 123 Calculations of the orbital energies by nonrelativistic and relativistic SCC-Xa-DV (for the methods, see [9] and [10], respectively) were performed for sixteen molecular orbitals: 5alg, 4tlu' 3eg, 6a19, 5tlu' seven valence orbitals (see above), 3t29 , 5eg, 8alg, and 8tlu (unoccupied orbitals). For the relativistic level splittings and shifts see the paper [11]. The results for the seven valence orbitals are shown in Fig. 43 [12]. An SCF-Xa-DV calculation yielded the energy of the nine orbitals 4eg through 5eg [2]. nonrelat. relat. -11 5t1u -""''':::::..- ---B- ...... --6- :> '" 7°19-...... ::: -12 ...... -6+ >- ~ '"c u.J "0 -13 Fig.43. Comparison of nonrelativistic and rela ~ tivistic eigenvalues. The notation 6+, ... stands for yt, ... [12]. -14 -15 The bonding orbitals are mainly 4eg and 2t2g (Mo 4d orbitals interacting with F 2pa and F 2pJt orbitals, respectively) [2,6]. The remaining valence orbitals, 7a19 through 1t19 , are predominantly ligand orbitals [2]. Hybridized Mo orbitals 4d25s5p3 allowing for a bonds (see [13]) were used in an early discussion of the molecular force field (see p. 139) [14]. The nephelauxetic effect and back bonding were considered to explain the bond order of 1.34 [15]; for Jt bonding due to donation of f1uorine p electrons, see [16]. Gross atomic charges and gross Mo orbital populations were obtained from Mulliken population analyses, based on a model-potential quasi-relativistic calculation in the Hartree Fock-Roothaan scheme [4] and on an SCF-Xa-DV calculation [2]: Mo F Mo 5s Mo 5p Ref. +1.88 -0.31 3.04 0.61 0.48 [4] +1.229 -0.205 1.522 2.590 0.366 0.331 [2] An atomic charge of about + 2 at Mo was also inferred from calculations for the related WF6 molecule [12], also see [6]. An atomic charge of -0.35 at F was calculated by a simple non quantum chemical approach [17]. References: [1] Sakai, Y.; Miyoshi, E. (J. Chem. Phys. 87 [1987] 2885/92). [2] Gutsev, G. L.; Levin, A. A. (Chem. Phys. 51 [1980] 459/71, 466/9). [3] McDiarmid, R. (Chem. Phys. Letters 76 [1980] 300/3). [4] Karisson, L.; Mattsson, L.; Jadrny, R.; Bergmark, T.; Siegbahn, K. (Phys. Scr. 14 [1976] 230/41, 235/9). Gmelin Handbook Mo Suppl. Vol. B 5 124 Molybdenum Fluorides [5] McDiarmid, R. (J. Chem. Phys. 61 [1974] 3333/9). [6] Bloor, J. E.; Sherrod, R. E. (J. Am. Chem. Soc. 102 [1980] 4333/40). [7] TopoI', I. A.; Dement'ev, A. 1.; Rambidi, N. G.; Nefedov, V. I. (Koord. Khim. 5 [1979]860/5; Soviet J. Coord. Chem. 5 [1979] 676/80). [8] Onopko, D. E. (Khim. Fiz. 5 [1986]1572/4; C.A. 106 [1987] No. 75093). [9] Rosen, A.; Ellis, D. E.; Adachi, H.; Averill, F. W. (J. Chem. Phys. 65 [1976] 3629/34). [10] Rosen, A.; Ellis, D. E. (Chem. Phys. Letters 27 [1974] 595/9, J. Chem. Phys. 62 [1975] 3039/49). [11] Rosen, A.; Fricke, B.; Morovi6, T.; Ellis, D. E. (J. Phys. Colloq. [Paris] 40 [1979] C4-218/C4- 219). [12] Rosen, A.; Fricke, S.; Morovi6, T.; Ellis, D. E. (Extend. Abstr. 5th Intern. Conf. Vac. Ultraviolet Radiat. Phys., Montpellier, Fr., 1977, Vol. 2, pp. 40/2; C.A. 89 [1978] No. 171066). [13] Craig, D. P.; Maccoll, A.; Nyholm, R. S.; Orgel, L. E.; Sutton, L. E. (J. Chem. Soc. 1954 332/53, 341). [14] Linnett, J. W.; Simpson, C. J. S. M. (Trans. Faraday Soc. 55 [1959] 857/66, 864). [15] Uendling [Wendling], E.; Makhmudi [Mahmoudi], S. (Opt. Spektroskopiya 32 [1972] 492/500; Opt. Spectrosc. [USSR] 32 [1972] 257/61). [16] Canterford, J. H.; Colton, R.; O'Donnell, T. A. (Rev. Pure Appl. Chem. 17 [1967]123/32, 126). [17] Mai, L. A. (Latvijas PSR Zinatnu Akad. Vestis Kim. Sero 1980 No. 3, pp. 304/7; C.A. 93 [1980] No. 123214). 2.2.8.2.3 lonization Potentials Ei' Photoelectron Spectrum The following table shows the adiabatic (ad) and vertical (vert) ionization potentials Ei (in eV) measured in an Hel-induced photoelectron (PE) spectrum [1]. The six observed PE bands [1] were assigned toseven molecular orbitals [2 to 4]. This assignment was supported by the vibrational structure observed in [1], by comparisons with the UV absorption spectrum (see p.160), and by theoretical calculations (see preceding section). The error limits given in parentheses apply to the last digit of the experimental Ei values [1]. Remarks are given below. Ei (ad) in eV ...... 14.7 15.5 16.553(4) 17.617(3) 18.122(7) 18.93(1) Ei (vert) in eV ...... 15.07(2) 15.80(2) 16.553(4) 17.617(3) 18.526(3) 19.076(5) assignment [2 to 4, 6] 11'9 15.5 eV Band~ A Jahn-Teller instability (or the ionization. from two different orbitals) was considered in [1] (band assigned to 7t,u only). 16.553 eV Band. The vibrational structure was explained by the ionic vibrations v, and v, +vs (features at 16.635 and 16.679 eV, respectively) [1]. 17.617 eV Band. Three vibrational features were assigned to vs, v" and v, +vs ionic vibrations [1]. For the assumed a'9 state only v, is a possible vibrational mode. Small deviations from the 0h symmetry would allow the excitation of Vs [2]. 18.122 eV Band. A vibrational progression was observed with a spacing of -79 meV C~640 cm-'), which was assigned to v, (the progression extends up to 6 v,) [1]. 18.93 eV Band. A vibrational progression with an approximate spacing of 73 meV (~590 cm-') was tentatively assigned to the V2 mode [1]. An excitation of V2 is consistent with eg symmetry of the electron orbital involved [2]. Gmelin Handbook Mo Suppt. Vot. B 5 MoF6 125 Theoretical calculations of ionization potentials made use of the transition state concept. For ionization from the 1t1g level, various methods (for abbreviations, see preceding section) yielded Ei = 14.4 (relativistic SCC-Xa-DV) (5), 14.97 (SCF-Xa-SW with overlapping atomic spheres) (3), and 15.17 (SCF-Xa-DV) (6). SCF-Xa-SW calculations were performed for various radii of tangent atomic spheres and various degrees of overlap of spheres [2,7). References: (1) Karisson, L.; MaUsson, L.; Jadrny, R.; Bergmark, T.; Siegbahn, K. (Phys. Scr. 14 (1976) 230/41,235/9). (2) Topoi', I. A.; Dement'ev, A. 1.; Rambidi, N. G.; Nefedov, V. I. (Koord. Khim. 5 (1979)860/5; Soviet J. Coord. Chem. 5 (1979) 676/80). (3) Bloor, J. E.; Sherrod, R. E. (J. Am. Chem. Soc. 102 (1980) 4333/40). (4) McDiarmid, R. (Chem. Phys. LeUers 76 (1980) 300/3). (5) Rosen, A.; Fricke, B.; Morovi6, T.; Ellis, D. E. (Extend. Abstr. 5th Intern. Conf. Vac. Ultraviolet Radiat. Phys., Montpellier, Fr., 1977, Vol. 2, pp. 40/2; C.A. 89 (1978) No. 171066; J. Phys. Colloq. [Paris) 40 (1979) C4-218/C4-219). (6) Gutsev, G. L.; Levin, A. A. (Chem. Phys. 51 (1980) 459/71, 467). (7) Onopko, D. E. (Khim. Fiz. 5 (1986)1572/4; C.A. 106 (1987) No. 75093). 2.2.8.2.4 Electron Affinity A All experimental and theoretical investigations of A (in eV) agree as to a high value, i.e. A ~3, and also to a value higher than that of the related WFs moleeule. The exact figure is, however, still controversial. Experimental data for MoFs range from A = 3.6 ± 0.2 [1,4) up to A = 5.68 reported in a study of the intercalation of MoFs into graphite (2). The values are arranged by increasing magnitude in the table below. The differences A(MoF6)-A(WF6) given at the end of the table were estimated from charge-transfer (CT) absorption spectra of both moleeules with various electron donors in the condensed phase. A(MoF6) >A(WF6) was also indicated by the CT studies [14 to 16). A(MoF6) in eV method Ref. remarks 3.6±0.2 ion-molecule reaction equilibrium constants [1,4) a) 3.83 ion-molecule reaction equilibrium constants (5) b) -3.8 CT with benzene (6) c) ~4.51 ion-pair formation in crossed thermal MoFs [7] d) and potassium beams ~5.1~8:§ ion-pair formation by Na atoms (3) e) 5.36±0.06 thermochemical cycles with MMoFs (8) f) 5.68 electron attachment in a mass spectrometer (2) g) A(MoFs)-A(WFs) 0.91 CT with aromatic hydrocarbons and fluorocarbons (6) 1.26 CT with Xe(solid) (9) h) a) Complicated gas phase equilibria, involving also beryllium fluoride species, have been evaluat ed in (4). Experimental studies trom the period 1974 to 1980 were included in the survey (1). b) Gas-phase equilibria evaluated; similar to al. c) Comparison with analogous CT spectra of the I atom [11,12), using A(I) = 3.06 eV. CT sensitive to phase transition (thermochrornism). G meUn Handt)ook Mo Suppt. Vol. B 5 126 Molybdenum Fluorides d) ldentical lower limits A~ D(K2) + Ei(K) = (0.51 + 4.34) eV for both MoFs and WFs would be derived if K2 molecules rather than K atoms reacted according to MoFs(WFs) + K2~ MoF6"(WF6") + K+ + K. e) ldentical limits for A(MoFs) and A(WFs) were obtained with Na atoms at center of mass energies ranging from 0 to -16 eV. The low value 3.89 eV from an earlier report [20) of the same authors might be due to the presence of alkali dimers (then not recognized) in the alkali metal beam used [3). f) From measured formation enthalpies and calculated lattice energies, M = K, Rb, Cs. The WFs value (5.07 ± 0.05) [8) was later modified to 4.63 [13). g) The paper [2) deals with MoFs intercalation into graphite. The estimated A value cited seems to stem from unpublished work. The value fits into an approximately linear relationship between the degree of CT observed for intercalation and A of several metal hexafluorides (Mo, Tc, Re through Pt) [2). h) The onset frequency of intermolecular CT MoFs(WFs)<-Xe at liquid N2 temperature was 26300(36600) cm-1. An outdated WFs affinity of 4.51 eV, see remark e), then gave A(MoFs) = 5.77 [9). Theoretical calculations by a quasi-relativistic model-potential (QRMP) configuration interaction (Cl) method, applied to MoFs and MoF6", gave adiabatic values A=6.66 (5.33 for WFs) and, corrected by inclusion of an f function at Mo(W) and a d function at F, 5.37 (3.85 for WFs) [21). A = 8.52 and a vertical value A = 8.07 had been calculated without Cl [10). A nonrelativistic Xa-SW calculation (with overlapping spheres) using the transition-state con cept yielded A = 4.50 (or 4.79, if relativistic effects were semi-empirically taken into account) up to A = 5.87, depending on the model used [18). An Xa-DV calculation of the 3t29 orbital energy of MoF6" led to A = 3.2 [19). References: [1) Sidorov, L. N. (Usp. Khim. 51 [1982)625/45; Russ. Chem. Rev. 51 [1982)356/67,359/60, 362/3). [2) Vaknin, D.; Davidov, D.; Selig, H. (J. Fluorine Chem. 32 [1986)345/60,347,352,357/8). [3) Compton, R. N.; Reinhardt, P. W.; Cooper, C. D. (J. Chem. Phys. 68 [1978)2023/36, 2025, 2027,2031). [4) Sidorov, L. N.; Borshchevsky [Borshchevskii). A. Ya.; Rudny [Rudnyi). E. B.; Butsky [Butskii). V. D. (Chem. Phys. 71 [1982) 145/56, 150). [5) Borshchevskii, A. Ya.; Sidorov, L. N.; Boltalina, O. V. (Dokl. Akad. Nauk SSSR 285 [1985) 377/81; Dokl. Phys. Chem. Proc. Acad. Sci. USSR 280/285 [1985)1109/12). [6) Hammond, P. R. (J. Chem. Soc. A 1971 3826/32). [7) Mathur, B. P.; Rothe, E. W.; Reck, G. P. (J. Chem. Phys. 67 [1977) 377/81). [8) Burgess, J.; Haigh, 1.; Peacock, R. D.; Taylor, P. (J. Chem. Soc. Dalton Trans. 1974 1064/6). [9) Webb, J. D.; Bernstein, E. R. (J. Am. Chem. Soc. 100 [1978) 483/5). [10) Sakai, Y.; Miyoshi, E. (J. Chem. Phys. 87 [1987) 2885/92). [11) Strong, R. L.; Rand, S. J.; Britt, J. A. (J. Am. Chem. Soc. 82 [1960) 5053/7). [12) Gover, T. A.; Porter, G. (Proc. Roy. Soc. [London) A 262 [1961) 476/88, 481). [13) Burgess, J.; Peacock, R. D. (J. Fluorine Chem. 10 [1977) 479/86). [14) Hammond, P. R.; McEwan, W. S. (J. Chem. Soc. A 1971 3812/9). [15) Hammond, P. R. (J. Phys. Chem. 74 [1970) 647/53). [16) Hammond, P. R.; Lake, R. R. (Chem. Commun. 1968987/8). [17) McDiarmid, R. (J. Chem. Phys. 61 [1974) 3333/9). Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 127 [18] BLoor, J. E.; Sherrod, R. E. (J. Am. Chem. Soc. 102 [1980] 4333/40). [19] Gutsev, G. L.; BoLdyrev, A. I. (Mol. Phys. 53 [1984] 23/31). [20] Cooper, C. D.; Compton, R. N.; Reinhardt, P. W. (ELectron. At. CoLLisions Abstr. Papers 9th Intern. Conf., Seattle 1975, VoL. 2, pp. 922/3). [21] Miyoshi, E.; Sakai, Y.; Murakami, A.; Iwaki, H.; Terashima, H.; Shoda, T.; Kawaguchi, T. (J. Chem. Phys. 89 [1988] 4193/8). 2.2.8.2.5 Nuclear Magnetic Resonance (NMR). Nuclear Spin-Rotation Interaction In the 19F NMR spectrum of the Liquid there are six sateLLites due to spin-spin coupling between 19F (nucLear spin 1= 1/2) and 95Mo or 97Mo (both 1=%) [2,3], in addition to the singLe sharp line observed in [1]. WhiLe no change in the spectrum was observed on passing through the Liquid-soLid transition the spectra broadened out beLow the soLid-soLid transition so much that lines were no Longer observed [3]. The 95Mo and 97Mo NMR spectra aLso consist of septets [4]. The tabLe beLow shows resuLts for the coupling constant 1J(95.97Mo-19F): 1J in Hz .... 44 47.1 ±0.2a) 47.2b) spectrum ... 19F 19F 95.97Mo Ref. [2] [5] [4] a) VaLue cited as 1J(95Mo-19F) in [6,33]. - b) VaLue given in a figure for the 95Mo spectrum. In the text: 1J = 42.2 Hz. For 2JC 9F-19F), describing the coupling between two 19F nucLei (1: F-Mo-F = 90°) a vaLue of 73.9 Hz was caLcuLated [7]. 19F and 95.97Mo NMR were aLso studied in both of the solid modifications (orthorhombic beLow -9.6°C, cubic or "pLastic" above), see beLow and p. 130, respectiveLy. The resoLved 19F NMR spectrum was observed [3] in the cubic modification but not in theorthorhombic modification. For the 19F NMR, considered beLow first, data are given for the chemical shift I) (in ppm; 1)<0 for shifts to Lower fieLd), for the shielding constant 0 (in ppm), for the spin-rotation interaction constant C (in kHz), and for the spin-lattice and spin-spin relaxation times T1 and T2• The 95.97Mo NMR data (p. 130) yieLd a nucLear quadrupoLe coupling constant. The sign convention for I) was used in the research papers cited beLow and conforms to the sign of the shieLding factor. The reversed convention, 0>0 for Low fieLd shifts, recommended in [36] was adopted onLy in the review paper [8]. The 0 vaLues refer to liquid CFCL3 as standard and primed symboLs refer to other standards. 19F NMR A chemicaL shift 0' = - 355 against CF3COOH was measured in the liquid (probabLy at room temperature) [2]; this shift vaLue for the Liquid was aLso indicated in a shift vs. temperature pLot, however, without stating the standard used [10]. With the shift of on = + 78.5 for CF3COOH against CFCL3 given in [8] this 0' vaLue corresponds to 0 = - 276.5; with on = 77 the vaLue 0=-278 was obtained [9]; 0=-282±0.5 was measured in [5]. For the cubic modification, 0' = - 357 measured against CF3COOH [10]. The spectrum of the orthorhombic modification was measured at -15 and -110°C [11] and down to -160°C [10]. A shift 0'=-363 against CF3COOH was found above -54°C [10]. At Gmelin Handbook Mo Suppl. Vol. B 5 128 Molybdenum Fluorides lower temperatures, the speetrum eonsisted of two eomponents (pointing to a tetragonal distortion of the MoF6 oetahedra [10,11]). The shifts are ö'=-175 and =-440 against CF3COOH and indieate four short and two long Mo-F bonds [10]. For the center of gravity, a shift of -550±30 (against HF) was obtained [11]. Chemieal shifts of binary fluorides and eomplex anions, ineluding MoF6 , were used to establish a linear relationship to (ealeulated) atomie eharges on the F atoms (see p. 123) [12]. An isotropie shielding constant 0iso = - 89 (± 30) [13] follows from the above ö = - 278, if the 19F shielding is scaled to 0(CFCl3) = 188.7 (and o(HF) = 410.0) give"n in [14]. For the separation of the shielding constant into a diamagnetic and a paramagnetic term see [15]. A shielding anisotropy ~o = 011- 0.L = - 300 (components parallel or perpendicular to an Mo-F bond) was derived from the field (or frequency) dependence of the spin-lattice relaxation time Tl measured in the solid [16]. Equatorial and axial sites of the MoFa octahedron have different values for 0.L and Oll; the differences 0.L - Oll are, however, nearly equal for both of these. From a relaxation study I ~o 1= 330 ± 70 was derived in agreement with I~o 1= 350 from a line-shape study [17]" The estimated I~o 1= 300 ± 200 was given earlier [11] obviously revising the 1~01=880 [18,32]. Components 011 =-289 and 0.L=+11 resulted from 0i80= 1/3(01l+20.L)=-89±30 and ~0=-300 [13]. Nuclear Spin-Rotation Coupling Constant C. The average of this constant was given as 2:n:C" = (-)20.3 kHz and its anisotropy as 2:n:(C II -C.L) = (-)9.9 kHz [16] (2:n:C is normally used in NMR; C is used in microwave spectroscopy, see [19]). The quantity C2=1;3(C~+2Ci)=C2+%(CII-C.L)2 is related to the rate of~laxation due to spin-rotation interaction (see below). The results trom [1~ given above yield C2 v, = (-)3.32 kHz [15]. For the effeetive constant, defined by C~tt=C2+%5(CII-C.L)2, the value 2:n:Cett = (-) 20.5 kHz is given [20], also see [21]. Relaxation Times. In the vapor, the spin-lattice relaxation time Tl was measured between 300 and 400 K at densities e = 1 to 8 Amagat (1 Amagat ~0.044617 moVL) [20, 21]. Tl /e (in ms/Amagat) decreased from 1.74 at 313 K to 1.40 at 363 K [21]. From a log-log plot of Tl /e vs. temperature T the relationship Tl /e oc y-n with n =1.49 ±0.04 [20] or 1.50 ± 0.06 [21] resulted. This shows that spin-rotation interaction is the dominant relaxation mechanism [20, 21]. Effective cross seetions for transfer of angular momentum in molecular collisions [20] and the anisotropic part of the intermolecular potential (see p. 142) [21] were derived from these data. In the liquid, Tl = 0.85 ± 0.1 s was measured at 23°C for frequencies between 2 and 56.4 MHz [5]. Tl decreased with increasing temperature from 1.03 s at 18°C to 0.60 s at 84°C according to Tl =Tl ", exp (E/kT) with Tl ",=0.076 sand E,=0.07 eV [16]. For the decrease of Tl with increasing T, see also graphs in [17, 18,22]. This temperature dependence and the indepen dence from frequency point to spin-rotation interaction as the main relaxation mechanism [16, 22]; also see [5, 23]. In the cubic mOdification, the spin-lattice relaxation time Tl was measured at 2 to 56.4 MHz. At high frequencies (30 or 56.4 MHz) the behavior of Tl resembles that of Tl in the liquid: independence of the frequency and a slight increase with decreasing temperature (for the liquid-like behavior of this "plastic" modification, see p. 148). At ~9.3 MHz, Tl decreases with decreasing frequeney and increases more strongly with decreasing temperature [17, 25] (this temperature dependence of Tl was also found by [18, 22]). The spin-spin relaxation time T2, on the other hand, is frequency-independent between 30 and 9.3 MHz and decreases from - 0.02 s at the melting point (m.p.) to - 0.002 s at the solid-solid transition. The T2 and the low frequency Tl results are accounted for by translational diffusion modulating the dipolar interaction (see the theory in [24]). The residence time ll,an8L between the diffusional jumps varies from 0.07 !JS at the m.p. to 0.64 !JS at the solid-solid transition. The derived activation GmeLin Handbook Mo SuppL. VoL. B 5 MoF6 129 energy EtranSl = 0.56 ± 0.01 eV (for the diffusion eoeffieient derived, see p. 147) [17, 25]. For plots of 1:transl vs. inverse temperature for various hexafluorides see [26]; for a review on NMR studies of ultraslow motions see [28]. The T, at high frequeneies was lower than ealeulated from eonsideration of translational diffusion alone. This suggests that the spin-rotation interaetion is also modulated by librational and rotational motions [17,25]. Assuming the high-frequeney T, to result from moleeular rotations, a eharaeteristie time 1:J = 0.4 ps at the solid-solid transition was derived [23], also see [17]. For an Arrhenius plot of 1:J eomparing MoF6 with other globular moleeules see [27]. In the orthorhombic modifieation, T, was measured down to - 60°C [18,22] and down to about -150°C [11, 17] and is given in Arrhenius plots of T, (note that T, is in ms in [11] and in s in [17,18,22]). At the solid-solid transition temperature, T, is roughly a faetor 40 lower than in the eubie modifieation [11,17,18,22]. At lower temperatures, strong ehanges of T, were observed. T, deereased with deereasing T to a minimum value T, = 14.5 ± 1 ms near - 20°C with 9.3 MHz [17] and T, = 17.8 ms at -17"C with 9.2 MHz [18, 22]. The minimum was less distinet with 15.2 and 22.9 MHz [18,22]. Below about - 20°C, a steep linear inerease of log T, with inereasing 1fT was observed at all frequeneies used [11, 17], T, reaehing, e.g., -13 s at about - 85°C and 9.3 MHz [17]. Below -90°C, T, va ried only slightly, reaehing -100 s at -150°C [11,17]. A eontinuous wave measurement gave T, = 95 ± 10 s at -147"C and 110 ± 10 s at -164°C [35]. Aetivation energies E (in eV) were derived from Arrhenius plots of T, between the T, minimum temperature and -90°C as folIows: E=0.5 [17] (0.50±0.01 [34]), 0.48 [18,22] (obviously revising the 0.38 eV given in [11]). The behavior of T, below - 90°C was aseribed to paramagnetie impurities in the early paper [11] and was later diseussed in terms of rare reorientational jumps of the librating MoF6 moleeules [17]. The behavior of T, above - 90°C refleets a thermally aetivated, hindered rotation of the MoF6 oetahedra. This involves a distortion of the moleeules because of the interehange of nonequivalent Mo-F bonds and modulates the dipolar energy and, beeause of the anisotropie ehemieal shift, also modulates the Zeeman energy [11]. These rotations are quasi-isotropie; see the detailed theoretieal analysis in [17]. The moleeules in the solid state rotate indepen dently [32]. For the time interval 1: between the moleeular reorientations, the following values were given: 1:=5 ns at -9.4°C [34],1:=6.4 ns at -17°C (the T, minimum temperature) [18], 1:=20 ns at -25°C (trom T'zfT'r=1, see below) [32], and 1:=48!1S at -90°C [34]. Other relaxation times were measured in the presenee of strong radio frequeney fields H, (defining the x axis) rotating at an angular veloeity 00 elose to the Larmor frequeney Wo = y. Ho about the eonstant field Ho (defining the z axis). These measurements yield three relaxation times, T,z' T,x' and T'd in the eoordinate system fixed to H, ("rotating frame"). T,z is the eonventional T, (and results have already been referred to above). T,x is a "transverse" spin lattiee relaxation time (see [29,30]). T'd is related to a "loeal field" Hd (mainly the dipole-dipole interaetion, see [31]) and is related to the seeond moment. At resonanee (00 = wo) the relaxation time T,r is obtained: (H~+ H~)fT'r= H~fT,x + H~fT'd (see [32,33]). The ratio T'zfT'r was measured down to - 55°C, the results being given by an Arrhenius plot of T,zfT'r. These plots indieate an aetivation energy of 0.33 eV [32,33] (rather than the - 0.5 eV from the T, data referred to above). The T'zfT'rmeasured at H, = 0.75 and 0.42 G at a frequeney of 8 MHz was slightly above 1 down to - -23°C. Asteep risewas observed between -23 and -56°C. At -40°C, T'zfT'x=16 and T,zfT'd = 12 [32,33]. T'd was measured with 10 MHz down to -140°C. It showed a hump at the T, minimum temperature and deereased from -8 ms at -9.4°C to -0.3 ms near -62°C. The Arrhenius plot of T'd shows a linear inerease with inereasing 1fT from - 0.6 ms at -100°C to -4 s at -140°C [34]. The eontinuous wave NMR speetra yield T'd = 9 ± 1 s at -147"C and 30 Gmelin Handbook Mo Suppl. Vol. B 5 9 130 Molybdenum Fluorides or 32 (± 5) s at -164°C [35]. The T1d measurements below - 90°C show that 1: can be described in the whole orthorhombic range by a single activation energy, E = 0.495 ± 0.005 eV (1: = 5.5 ns to 4 s). Thus, molecular reorientations take place at these low temperatures [34]. The relaxation behavior of (UF6lx(MoF6)1-X solid solutions was studied in [6,27]. 95,97Mo NMR Strong quadrupole effects were observed for a rnagnetic fjeld of 11.7 T in the liquid, cubic, and orthorhombic phases. In the liquid (at 297 K), a septet appeared due to coupling with the six 19F nuclei. In the cubic modification, the spectrum was less weLl resolved. The 97Mo linewidth was dominated by quadrupole relaxation. In the orthorhombic modification (at 253 K), the 95Mo spectrum showed a quadrupole structure; the 97Mo spectrum consisted of a single asymmetrie and enlarged transition, shifted by a quadrupole effect of second order. Quadrupole coupling constants were eqQ=12.0±1.0 for 95Mo and 130±10 kHz for 97Mo. Asymmetry parameter of the electric field gradient, 1] = 0.37 ± 0.05 [4]. An MO_19F double resonance in a rotating frame had led to eqQ=140±20 kHz (probably for 97Mo, although described as 95Mo_19F double-resonance experiment) and 1] = 0.3 ± 0.1 [37]. References: [1] Gutowsky, H. S.; McCaLl, D. W.; Slichter, C. P. (J. Chem. Phys. 21 [1953] 279/92, 282). [2] Muetterties, E. L.; PhiLlips, W. D. (J. Am. Chern. Soc. 81 [1959] 1084/8). [3] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1563/8). [4] Brunet, F.; Le Bail, H.; Virlet, J. (Ann. Chim. [Paris] [15] 9 [1984] 771/4). [5] Rigny, P.; Demortier, A. (Compt. Rend. B 263 [1966]1408/10). [6] Virlet, J. (CEA-R-4344 [1973]1/161, 10,31/2,36/41,58/9; C.A. 80 [1974] No. 76378). [7] Yang, W. (Bopuxue Zazhi 1 [1984]137/42; C.A. 104 [1986] No. 178919). [8] Wray, V. (Ann. Rept. NMR Spectrosc. 14 [1983]1/406,5). [9] Emsley, J. W.; Phillips, L. (Progr. Nucl. Magn. Resonance Spectrosc. 7 [1971]1/526, 166, 500,504). [10] Afanas'ev, M. L.; Gabuda, S. P.; Lundin, A. G.; Opalovskii, A. A.; Khaldoyanidi, K A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 4, pp. 18/22; C.A. 70 [1969] No. 52864). [11] Blinc, R.; Pirkmajer, E.; Slivnik, J.; Zupancic, I. (J. Chem. Phys. 45 [1966]1488/95). [12] Mai, L. A. (Latvijas PSR Zinatnu Akad. Vestis Kim. Sero 1980 No. 3, pp. 304/7; C.A. 93 [1980] No. 123214). [13] Applernan, B.R.; Dailey, B. P. (Advan. Magn. Resonance 7 [1974] 231/320, 263, 278). [14] Hindermann, D. K.; CornweLl, C. D. (J. Chem. Phys. 48 [1968] 4148/54). [15] DevereLl, C. (Mol. Phys. 18 [1970] 319/25). [16] Rigny, P.; Virlet, J. (J. Chem. Phys. 47 [1967] 4645/52). [17] Rigny, P.; Virlet, J. (J. Chem. Phys. 51 [1969] 3807/16). [18] Blinc, R.; Lahajnar, G.; Pirkmajer, E.; Zupancic, I. (Proe. CoLloq. AMPERE 14 [1966/67] 1068171; C.A. 70 [1969] No. 15794). [19] Spiess, H. W. (NMR Basic Princ. Progr. 15 [1978] 55/214, 155). [20] Ursu, 1.; Bogdan, M.; Fitori, P.; Darabont, A.; Demco, D. E. (Mol. Phys. 56 [1985] 297/302). [21] Ursu, 1.; Bogdan, M.; Balibanu, F.; Fitori, P.; Mihailescu, G.; Demco, D. E. (Mol. Phys. 60 [1987] 1357/66). [22] Blinc, R.; Lahajnar, G. (Fizika [Zagreb]1 [1968]17/29,24,26; C.A. 70 [1969] No. 72747). Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 131 [23) Rigny, P.; Drifford, M.; Virlet, J. (J. Phys. Colloq. [Paris) 32 [1971) C5a-229/C5a-232). [24) Resing, H. A.; Torrey, H. C. (Phys. Rev. [2)131 [1963)1102/4). [25) Virlet, J.; Rigny, P. (Compt. Rend. B 267 [1968)1238/40). [26) Virlet, J.; Rigny, P. (Chem. Phys. Letters 6 [1970) 377/80). [27) Virlet, J.; Rigny, P. (J. Magn. Resonance 19 [1975) 188/207, 201/2). [28) Ailion, D. C. (Advan. Magn. Resonance 5 [1971) 177/227,216/9). [29) Redfield, A. G. (Phys. Rev. [2) 98 [1955)1787/809, 1792). [30) Solomon, 1.; Ezratty, J. (Phys. Rev. [2)127 [1962) 78/87). [31) Hebel, L. C., Jr. (Solid State Phys. 15 [1963) 409/91, 447). [32) Rigny, P. (Compt. Rend. B 265 [1967)1058/61). [33) Rigny, P. (CEA-R-3464 [1969)1/84, 16,36,40/1; C.A. 71 [1969) No. 86416). [34) Virlet, J.; Rigny, P. (Chem. Phys. Letters 4 [1969170) 501/4). [35) Wind, R. A.; van Baren, B. A.; Emid, S.; Kroonenburg, J. A.; Smidt, J. (Physica [Amster dam) 65 [1973) 522/38). [36) IUPAC Commission on Molecular Structure and Spectroscopy (Pure Appl. Chem. 45 [1976) 217/9). [37) Kind, R.; Vi riet, J. (CEA-CONF-3846 [1976) 1; C.A. 88 [1978) No. 30023). 2.2.8.2.6 Electrical Multipole Moments of the Moleeule All moments up to the octopole moment vanish due to the 0hsymmetryof the moleeule. For the dipole moment, this was confirmed by deflection studies using a molecular beam in an electric quadrupole field [1). The hexadecapole moment was derived from the i9F spin-Iattice relaxation time T1 in the vapor (see p. 128). The temperature dependence of T1 was interpreted in terms of the aniso tropie part of the intermolecular potential (see p. 142). Using three models for the isotropie interaction, for (in 10-41 esu· cm4 ~ 33.36 x 10-60 C· m4) the values 1.03, 0.88, and 0.67 resulted for the hard-sphere, the Lennard-Jones- (12,6), and a modified Buckingham- (exp,6) potential, respectively [2) (the definition of used here yields values twice as large as would result from the definition used with SFs in "Schwefel" Erg.-Bd. 2, 1978, p. 122). References: [1) Kaiser, E. W.; Muenter, J. S.; Klemperer, W.; Falconer, W. E.; Sunder, W. A. (J. Chem. Phys. 53 [1970)1411/2). [2) Ursu, 1.; Bogdan, M.; Balibanu, F.; Fitori, P.; Mihailescu, G.; Demco, D. E. (Mol. Phys. 60 [1987)1357/66, 1365). 2.2.8.2.7 Rotational Constant B. Centrifugal Distortion Constants For the vibrational ground state, Bo = 0.0670 ± 0.0002 cm-1 [1) (2007.2 MHz [2)) was calcu lated from an Mo-F bond length of r =1.820 ± 0.003 A (see below). Centrifugal distortion constants DJ, DK, DJK, Rs, Rs, and öJ were calculated from different sets of force constants (see p.138), using relations given in [3) and the general expressions for DJ , DK, ... [4). For octahedral symmetry, DJK =_sI7DK, Rs=O, Rs=-DK/14, and öJ =0[5). DJ =108.3 and DK = -247.9 Hz were calculated on the basis of the MoFs vibrational frequencies given in [6) (see p.133) [5). Based on frequencies from [8) and assuming r=1.84 Aaset of six non vanishing distortion constants was calculated in [7). GmeLin Handbook Mo Suppt. Vol. B 5 9' 132 Molybdenum Fluorides For the vibrationalty excited V3 state, the rotational constant B3 was derived for the seven isotopic MoF6 species trom the corresponding IR absorption band, taken in a supersonic free jet. Two additional constants, a220 and a224' were also determined [2]. These appear as coefficients of vibration-rotation operators in the effective Hamiltonian (for Td symmetry) [9]. B3 - % a220 and B3 +% a220 are the effective rotational constants for the P- and R-branch and the Q-branch lines, respectively, see the WFa study [10]. Values for B3 and a224 are given in the foltowing table [2]: isotope .... 92MoF6 ~Mo~ ·Mo~ %Mo~ 97MoFa 96MoF6 l00MoFa B3 in MHz. .. 2005.59 2005.548 2005.496 2005.531 2005.44 2005.62 2005.74 a224 in kHz .. 337 310 310 299 281 319 288 a220 was fixed at 809 kHz for alt isotopic species [2]. Effective perturbations of the Q-branch rotational constants were previously measured for three isotopic species containing 92Mo, %Mo, and looMo [11]. References: [1] McDowelt, R. S.; Sherman, R. J.; Asprey, L. B.; Kennedy, R. C. (J. Chem. Phys. 62 [1975] 3974/8). [2] Takami, M.; Matsumoto, Y. (Mol. Phys. 64 [1988]645/58, 652), Matsumoto, Y.; Takami, M. (Reza Kagaku Kenkyu 8 [1986]13/5; C.A. 106 [1987] No. 164845). [3] Kivelson, D.; Wilson, E. B., Jr. (J. Chem. Phys. 21 [1953]1229/36). [4] Kivelson, D.; Wilson, E. B., Jr. (J. Chem. Phys. 20 [1952]1575/9). [5] Dhanalakshmi, A.; Lalitha, M. (Bult. Classe Sci. Acad. Roy. Belg. [5]68 [1984] 249/58). [6] Weinstock, S.; Goodman, G. L. (Advan. Chem. Phys. 9 [1965] 169/319, 199). [7] Sabapathy, K.; Ramasamy, R. (Indian J. Phys. B 58 [1984] 464/72). [8] Claassen, H. H.; Goodman, G. L.; Holtoway, J. H.; Selig, H. (J. Chem. Phys. 53 [1970] 341/8). [9] Robiette, A. G.; Gray, D. L.; Birss, F. W. (Mol. Phys. 32 [1976] 1591/607, 1599). [10] Takami, M.; Kuze, H. (J. Chem. Phys. 80 [1984] 5994/8). [11] Cummings, J. C. (J. Mol. Spectrosc. 83 [1980] 417/30, 427). 2.2.8.2.8 Atomic Distances r. Inertial Defect Electron diffraction on an MoFa jet (nozzle temperature - 20°C) yielded an Mo-F distance (in A) of rg '" 1.820 ± 0.003 and indicated 0h symmetry for the molecule [1] (the subscript "g" refers to the center of gravity of the probability density, see [4]); also see the review [2] and the paper [3]. For the Mo-F and F-F distances, slightly modified by shrinkage effects, see [1 to 3]. The values r'" 1.840 [5], r = 1.84 ± 0.02 [6, 8]. and r'" 1.84 [9] are apparenHy cited from the unpublished electron diffraction measurement [7]. Early electron diffraction studies suffered from the use of real rather than complex scattering lengths and yielded two different Mo-F distances [10, 13 to 16]. For cubic MoFa a single r(Mo-F) =1.802 resulted [17] while for the orthorhombic modifica tion Mo-F distances of 1.766 to 1.861, mean distance r=1.809, were measured by neutron diffraction [18]. Equilibrium Mo-F distances re =1.849 [19] and 1.881 [12] were theoreticalty calculated using model-potential methods and taking major relativistic effects into account. The Badger Gmelin Handbook Mo Suppt. Vot. B 5 MoF6 133 ruLe [20] was used to derive the Mo-F distance from vaLence force constants, r=1.83 [22], but when using the extension [21] of that ruLe, r=1.69 resuLted [23]. For the oLd estimate r =1.90, see [14]. An increase of the Mo-F distances in severaL eLectronicaLLy excited states was inferred from the reduction of the frequencies of the totaLLy symmetric Mo-F stretching vibration v, (A,g) in these states (see p. 135) [24, 25]. The vaLue ~=0.1418 u ·A2 was caLcuLated [27] for the correction termed "inertiaL defect" [26] (and reLated to the apparent shrinkage). References: [1] Seip, H. M.; Seip, R. (Acta Chem. Scand. 20 [1966] 2698/710, 2706). [2] Seip, H. M. (SeLec. Top. Struct. Chem. 1967 25/68, 57). [3] Cyvin, S. J.; Cyvin, B. N.; BrunvoLL, J.; Andersen, B.; St0Levik, R. (SeLec. Top. Struct. Chem. 196769/89, 84). [4] BarteLL, L. S. (J. Chem. Phys. 23 [1955]1219/22). [5] CLaassen, H. H.; SeLig, H.; MaLm, J. G. (J. Chem. Phys. 36 [1962] 2888/90). [6] StuLL, D. R.; Prophet, H. (JANAFThermochemicaL TabLes, 2nd Ed., NSRDS-NBS-37 [1971 D. [7] Nazarian, O. (private eommunieation to [5], see aLso [11 D. [8] Gutsev, G. L.; BoLdyrev, A. I. (Mol. Phys. 53 [1984] 23/31). [9] Cyvin, S. J. (MoLecuLar Vibrations and Mean Square AmpLitudes, UniversitetsforLaget, Oslo 1968, p. 130). [10] Braune, H.; Pinnow, P. (Z. Physik. Chem. B 35 [1937] 239/55, 244/5). [11] Nazarian, G. M. (Diss. CaLif. Inst. Teeh. 1957, Pt. 11). [12] Miyoshi, E.; Sakai, Y.; Murakami, A.; Iwaki, H.; Terashima, H.; Shoda, T.; Kawaguchi, T. (J. Chem. Phys. 89 [1988] 4193/8). [13] Bastiansen, O. (Tidsskr. Kjemi Bergvesen Met. 11 [1951]134). [14] Bauer, S. H. (J. Phys. Chem. 56 [1952] 343/51). [15] Sehomaker, V.; GLauber, R. (Nature 170 [1952] 290/1). [16] GLauber, R.; Schomaker, V. (Phys. Rev. [2] 89 [1953] 667/71). [17] Levy, J. H.; Sanger, P. L.; TayLor, J. C.; WiLson, P. W. (Acta Cryst. B 31 [1975]1065/7). [18] Levy, J. H.; TayLor, J. C.; WiLson, P. W. (Acta Cryst. B 31 [1975] 398/401). [19] Sakai, Y.; Miyoshi, E. (J. Chem. Phys. 87 [1987] 2885/92). [20] Badger, R. M. (J. Chem. Phys. 2 [1934]128/31,3 [1935] 710/4). [21] Jensovsky, L. (Z. Chem. [Leipzig] 2 [1962] 334/6). [22] Gaunt, J. (Trans. Faraday Soe. 50 [1954] 546/51). [23] Fadini, A.; KemmLer-Sack, S. (Z. Anorg. ALLgern. Chem. 436 [1977] 210/2). [24] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951] 1164/7). [25]' McDiarmid, R. (J. Chem. Phys. 61 [1974] 3333/9). [26] Hersehbach, D. R.; Laurie, V. W. (J. Chem. Phys. 40 [1964] 3142/53). [27] DhanaLakshmi, A.; LaLitha, M. (BuLL. CLasse Sei. Acad. Roy. BeLg. [5] 68 [1984] 249/58). 2.2.8.2.9 Fundamental Vibrations Vi in cm-'. Vibrational Amplitudes. Coriolis Coupling Constants The frequeneies of the three Raman-aetive vibrations, v,(A'g)' v2(Eg), and V5(F2g) and the frequeneies of the two IR-active vibrations, V3(F,u) and v4(F,u), were obtained from the respective vapor-phase spectra. The frequency of the siLent mode, V6 (F2u ), was derived trom Gmelin Handbook Mo Suppl. Vol. B 5 134 MoLybdenum Fluorides the Raman overtone 2V6 or from IR combination bands (for the spectra, see pp. 157ft.). Wavenumbers (in cm-1) of individuaL isotopic species are given first. They were measured with isotopicaLLy enriched sampLes or by tunabLe Laser spectroscopy (at reduced temperatures). The foLLowing tabLe for 92MoF6 and 1ooMoF6 shows the Q-branch maxima forv1' V2' V4' and vs. For the V3 vaLue, the band origin was estimated from the position of the high-frequency edge of the Q branch. For the vaLue of V6' one haLf of the 2v6 Q-branch maximum was adopted. The isotopic purity of the Mo used was ~97.4%. The V1' V2' Vs, and 2 V6 vaLues for 92MoF6 were taken in [1] from the Raman data of 1ooMoF6, which was most compLeteLy investigated (no significant frequency difterences were observed between 92MoF6 and 100MoF6). IR data were taken at 300 and 200 K [1]: isotope v1(A19 , Ra) 741.8±0.3 652.0±0.5 749.5±0.5 265.7±0.5 317±1 117b) 1ooMoF6 741.8±0.3 652.0±0.5 741.4±0.5a) 262.7±0.5a) 317±1 117b) a) Isotopic shifts in cm-1 with respect to 92MoF6: -8.1 ±0.3 for V3' -3.0±0.4 for V4. - b) 2V6=233±2 cm-1. Using a tunabLe diode Laser, the V3 band origins of aLL seven isotopic species were measured by IR absorption spectroscopy on a supersonic free jet of naturaL MoF6 [2] (Last digit of the originaL data omitted): isotope 92MoF6 94MoF6 ~Mo~ %Mo~ ~Mo~ 9BMoF6 1ooMoF6 V3 in cm-1 ...... 749.489 747.364 746.3247 745.3001 744.289 743.294 741.340 Isotopic shift (in cm-1 per atomic mass unit) ßV3/ßA= -1.018 [2]. Consistent shifts were previousLy measured for the V3 Q branch of 92MoF6, %MoF6, and 1ooMoF6, using isotopicaLLy pure sampLes at 195 and 80 K [3]. These resuLts of [3] cLoseLy foLLow the relationship ßvslßA= -4.20·V3·A-1.7S [4]. Isotopic shifts ßV3 and ßV4 were aLso derived from the set of moLecuLar force constants [5]. The foLLowing tabLe contains vibration frequencies (in cm-1) from measurements with naturaL MoF6. These Raman and IR data suffer from a severe overLapping of both isotopic and hot bands. The V6 vaLue is haLf the frequency of the observed overtone 2v6 [8, 9]. V1 ...... 741.6±0.5 741.5±0.3 741 V2 ...... 650.9 ± 0.5 651.6 643 V3 ...... 741.1±0.3 741 V4 ...... (264) 262 Vs ...... 318.4±0.5 318 (312) V6 ...... 114.5 ± 1 116 (122) source Raman spectrum Raman, IR spectra earLier survey c) remark .... a) b) Ref...... [8] [9] [10] a) Q-branch maxima; T = 378 K. - b) Raman study at 70°C; V4 from the earLier IR study [12]. - c) CriticaL examination of Raman [12] and IR data [12 to 14] from gaseous MoF6. The vaLue V6 = 122 cm-1 [10] was evaLuated from the reported IR combination bands and revised the earLier suggestions V6 =190 [12], 240 [13], and 234 cm-1 [14]. The vaLues V1= 739, V2 = 643, and Vs = 320 cm-1 [10] are approximate mean vaLues of the Raman frequencies observed in the Liquid state [14, 15]. Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 135 The Raman study [11] yielded V1 =742±0.8 cm-1• Vibronic progressions were observed in UV absorption bands of the vapor {see p. 160}. If assigned to the totally symmetric stretching vibration, they would indicate smaller V1 values for the excited states than the above V1 value of the ground state: V1 = 630 [16] or 639 cm-1 [15] in bands around 189 nm, V1 =609 cm-1 near 144 nm and 600 cm-1 around 123 nm [16]. Vibrational Amplitudes Root-mean-square amplitudes u {in 10-2 A} were obtained from an electron diffraction measu rement at a nozzle temperature of - 20°C [17] and -15°C [18]. For the Mo-F bond, the following value (reported in [18]) slightly revises the value given in [17]. The u values for Mo-F and for short {s} and long {l} F···F distances are: u{Mo-F}=3.55±0.4 [18], u{F···F,s}= 9.8±0.5 [17,18], u{F···F, l}=6.0±0.7 [17, 18]. Calculated u values {in 10-2 A} derived from more recent sets of Vi are given below. The experimental data or assumptions used to obtain a unique set of force constants are indicated {see p. 138}: Tin K u{Mo-F} u{F' .. F, s} u{F' .. F, l} Vi from unique force remark Ref. constants by 293 4.0 11.0 5.3 [1] isotopic shifts a) [1] 298 4.0 11.1 5.3 [1] L-F approximation b) [22] c) 293 3.99 10.92 5.33 [10] F34/F 44 = 4m F/{m MO + 2m F} [19] 0 3.87 7.48 5.11 [1] Coriolis coupling constants d) [23] 298 3.99 11.12 5.31 } 298 4.47 10.69 5.31 [9] Torkington [6] method [25] 500 5.11 13.36 5.90 } a) More accurate than the experimental results of [17, 18] according to [1]. b) Calculated for 92MoF6• The L-F approximation neglects the squares of the L-matrix element L34 and of F34• c) Another sign convention was used for F34 {see p. 138} in [19]. For the dependence of u on F34 , see graphs for 298 Kin [19]; also see [20]. The frequencies given in [10] were also used in [26,27]. d) Apparently using Coriolis coupling constants derived from the set of molecular force constants given in [1]. Calculations on the basis of fundamental frequencies Vi {or sets of molecular force constants} yield symmetrized {~ii' i, j = 1 to 6} or valence type {o"oa' ... } mean-square amp,litudes. One has, e.g., u2{Mo-F} = 0,= %~11 + V3~22+ V2 ~33 [20, 21] and ~11 = 0,+40,,+ 0", [21]. u2{Mo-F} is also termed a "parallel" mean-square amplitude, <öz2>. The so-called "perpendicular" amplitudes <öx2> = <Öy2> are given by % ~44 + 1;16 ~55 + % ~66 [20]. For a table of ° and ~ values see [25]. Parallel «öz2» and perpendicular {<öx2> = <Öy2>} amplitudes are calculated for 298 and 500 K [28]. The frequencies from [9] were also used in [29]. Outdated frequency sets {including too large a value of V6} were used to calculate values of u [31 to 34, 37], ~ [21, 24, 35, 36] and ° [21, 35, 37], Coriolis Coupling Constants Sij {i, j = 2 to 6} Coriolis coupling constants Sij depending on the set of molecular force constants {nontrivial Sij} belong to the following direct products of representations (symmetry species): F1u x F1u Gmelin Handbook MoSuppl.Vol.B5 136 MoLybdenum Fluorides (1 st-order constants ~33 = ~3 and ~ =~, 2nd-order constant ~34) and F1u x F2u (2nd-order constants ~3S and ~), see [19, 33]. The triviaL nonzero constants beLong to F29 x F2g (~55 = ~5)' F2u X F2u (~= ~), and to Eg x F2g (~25)' see [33]. The constant ~22 = ~2 (from Eg x Eg) is zero [38, 39]. The numericaL vaLues of the (nonvanishing) constants depend both on the choice of the moLecuLar axis system (x, y, z) and on that of the normaL coordinates (Qj., ... ; note that most of the normaL modes are degenerate). This is indicated by the fuLL designation ~\1.jb (a = x, y, z). In the foLLowing, unprimed constants refer to x, y, z axes going through the corners of the MoFs octahedron (see [20, p. 102]). Primed constants, on the other hand, refer to an axis system with z going through corners and x, y going through mids of edges (used in [33]). The choice of normaL coordinates used here for the unprimed constants foLLows McDoweLL's convention [38,39]; for further conventions required see [20, p. 131]. TriviaL (nonzero) constants and sum ruLes are given first. For the 1st-order constants of F1u , ~3 + ~ = V2 hoLds, see [19, 20, 38, 39] (or ~3 + tI = y'2/4, see [33]). For the 2nd-order constant ~34 (or ~3.t) the product ~·~-lJt=-V2 [23,30] (or ~3+t1-~=-% [33]). For the F1U xF2u constants, ~ + l;t, = % [20,23, 30] (~+ tIä = % [33]) hold. For F29 and F2u , ~5 = - V2 and ~ = - V2 [30, 38, 39]. The Eg x F2g reLated constant is ~25 = -1 [23,30]. The soLe experimentaL CorioLis constant seems to be adetermination of B~3 for individuaL isotopic species from a V3 absorption spectrum taken in a supersonic free jet. B~3 decreases from 558.6 ± 0.6 MHz for 92MoFs to 522.0 ± 0.5 MHz for 1OOMoFs [2]. With B = 2000 MHz (see p. 131), ~=0.28 for 92MoFs and =0.26 for 1ooMoFs. CorioLis coupLing constants were aLso deduced from the fundamentaL frequencies vjand the set of moLecuLar force constants. Since these caLcuLations make use of the sum ruLes it is sufficient to report expLicit data onLy for ~3 and ~s. ~3 = 0.233 for 92MoFs and ~3 = 0.212 for 1ooMoFs were deduced from isotopic frequencies and empiricaL force constants (based on the measured isotopic frequency shift). The observed contours of the V3 (and v4) absorption bands were consistent with these vaLues [1]. Further vaLues are (in parentheses: frequency set and assumption concerning the force fieLd) ~ = 0.30 (Vj(92MoFs) [1]; L-F approximation, see pp. 135,139) [22], 0.29 (vj(MoFs) [10]; F44 = min.) [27], 0.284 (v;[10]; F33/F44 = (-)4mF/(m MO + 2 mF)) [19, 20], ~3 = -0.157 (v j [9]; Torkington [6] method) [40], - 0.156 (vj [12]; F33 = max.) [33]. ~ was aLso derived from an empiricaL formuLa containing onLy the atomic masses for octahedraL moLecuLes [7]. ~3S = ± 0.598 (~s = ± 0.626) was caLcuLated (Vj from [10] and using F34/F 44 = (-)4 m F/ (m Mo +2mF)) [19]. ~= -0.626 [20]. ~3s=0.552 [33], ~3s=0.553 (~4s=0.264) [40]. References: [1] McDoweLL, R. S.; Sherman, R. J.; Asprey, L. B.; Kennedy, R. C. (J. Chem. Phys. 62 [1975) 3974/8). [2) Takami, M.; Matsumoto, Y. (Mol. Phys. 64 [1988]645/58, 652); Matsumoto, Y.; Takami, M. (Reza Kagaku Kenkyu 8 [1986]13/5; C.A. 106 [1987] No. 164845). [3] Cummings, J. C. (J. Mol. Spectrosc. 83 [1980] 417/30, 427). [4] McDoweLL, R. S. (Spectrochim. Acta A 42 [1986] 1053/7). [5] Atvars, T. D. Z.; ZaniqueLLi, M. E. D.; Lin, C. T. (Acta Sud Am. Quim. 3 [1983]37/48,43/4; C. A. 100 [1984] No. 147579). [6] Torkington, P. (J. Chem. Phys. 17 [1949] 357/69). [7] Timoshinin, V. S.; Godnev, I. N. (Dokl. Nauch. Tekh. Konf.lvanov. Khim. Tekhnol.lnst. 1971 3/5; C.A. 78 [1973] No. 153209). [8] Bosworth, Y. M.; CLark, R. J. H.; Rippon, D. M. (J. Mol. Spectrosc. 46 [1973)240/55, 242). Gmelin H.ndboak Mo Suppl. Val. B 5 MoF6 137 [9) CLaassen, H. H.; Goodrnan, G. L.; HoLLoway, J. H.; SeLig, H. (J. Chern. Phys. 53 [1970] 341/8). [10) Weinstock, B.; Goodrnan, G. L. (Advan. Chern. Phys. 9 [1965)169/319, 199, 310). [11) Cahen, J.; CLerc, M.; Isnard, P.; Rigny, P.; WeuLersse, J. M. (Nonlinear Behav. Mol. At. Ions ELectr. Magn. ELectrornagn. FieLds Proc. 31 st Intern. Meeting Soc. Chirn. Phys., Abbaye de Fontevraud, Fr., 1978 [1979), pp. 127/39, 132; C.A. 91 [1979) No. 65652). [12) CLaassen, H. H.; SeLig, H.; MaLm, J. G. (J. Chern. Phys. 36 [1962) 2888/90). [13) Gaunt, J. (Trans. Faraday Soc. 49 [1953) 1122/31, 1125). [14) Burke, T. G.; Srnith, D. F.; NieLsen, A. H. (J. Chern. Phys. 20 [1952) 447/54). [15) Tanner, K. N.; Duncan, A. B. F. (J. Am. Chern. Soc. 73 [1951)1164/7). [16) McDiarrnid, R. (J. Chern. Phys. 61 [1974) 3333/9). [17) Seip, H. M.; Seip, R. (Acta Chern. Scand. 20 [1966) 2698/710). [18) Seip, H. M. (SeLec. Top. Struct. Chern. 1967 25/68, 57). [19) Cyvin, S. J.; Cyvin, B. N.; BrunvoLL, J.; Andersen, B.; St0Levik, R. (SeLec. Top. Struct. Chern. 196769/89,79,81). [20) Cyvin, S. J. (MoLecuLar Vibrations and Mean Square ArnpLitudes, UniversitetsforLaget, OsLo 1968, pp. 130,240,369). [21) Nagarajan, G. (BuLL. Soc. Chirn. BeLges 72 [1963) 537/59, 540, 546/50, 558). [22) Verrna, U. P.; Sharrna, D. K.; Pandey, A. N. (Acta Ciencia Indica 3 [1977) 58/62; C.A. 87 [1977) No. 159286). [23) Chinnappan, V. A.; Natarajan, A. (Prarnana 18 [1982)501/9; C.A. 97 [1982) No. 225850). [24) Nagarajan, G. (Indian J. Pure Appl. Phys. 4 [1966) 237/43). [25) Nagarajan, G.; Adams, T. S. (Z. Physik. Chern. [Leipzig) 255 [1974) 869/88, 878/84). [26) Awasthi, M. M.; Mehta, M. L. (Spectrosc. LeUers 2 [1969) 327/31). [27) Thakur, S. N.; Rao, D.V.R.A.; Rai, D. K. (Indian J. Pure Appl. Phys. 8 [1970)196/8). [28) Nagarajan, G.; Adams, T. S. (Monatsh. Chern. 104 [1973)1607/22, 1616). [29) Sabapathy, K.; Rarnasarny, R. (Indian J. Phys. B 58 [1984) 464/72). [30) Mohan, S.; Kurnar, K. G. R. (Indian J. Pure Appl. Phys. 18 [1980) 857/63). [31) Singh, O. N.; Rai, D. K. (Can. J. Phys. 43 [1965) 378/82). [32) Kirnura, M.; Kirnura, K. (J. Mol. Spectrosc. 11 [1963) 368/77, 376). [33) Meisingseth, E.; BrunvoLL, J.; Cyvin, S. J. (Kgl. Norske Videnskab. SeLskabs Skrifter 1964/ 65 No. 7, pp. 1/49, 45, 48). [34) Meisingseth, E.; Cyvin, S. J. (Acta Chern. Scand. 16 [1962) 2452/3). [35) Nagarajan, G. (Current Sci. [India) 32 [1963) 64/5). [36) Sundararn, S. (Z. Physik. Chern. [N.F.) 34 [1962) 225/32). [37) UendLing [WendLing). E.; Makhrnudi [Mahrnoudi). S. (Opt. Spektroskopiya 32 [1972)492/ 500; Opt. Spectrosc. [USSR) 32 [1972) 257/61). [38)' McDoweLL, R. S. (J. Chern. Phys. 41 [1964) 2557/8). [39) McDoweLL, R. S. (J. Chern. Phys. 43 [1965) 319/23). [40) Nagarajan, G.; BrinkLey, D. C. (Monatsh. Chern. 104 [1973)1183/202, 1198/200). Gmelin Handbook Mo Suppl. Vol. B 5 138 MoLybdenum Fluorides 2.2.8.2.10 Vibrational Relaxation A singLe reLaxation process attributed to the totaL vibrationaL energy was inferred from a measurement of uLtrasonic attenuation at 293 K. At pressures p = 5 to 111 Torr, for the isothermal reLaxation time ,;, the product ,;. p = 2.8 X 10-8 s· atm resuLted [1]. A theoreticaL caLcuLation of the temperature dependence yieLded Log,; = - 9.3 + 25.3 x T-l13 (,; in s; presum abLy normaL pressure) [2]. References: [1] Bass, H. E.; Jensen, V.; EzeLL, J. (J. Chem. Phys. 77 [1982] 4164/8). [2] Doi, H.; Kono, Y.; Higashi, K. (J. Acoust. Soc. Am. 54 [1973]1267170). 2.2.8.2.11 Force Constants For the force constants of hexafluorides with 0h symmetry, see, e. g., the corresponding chapter on SFs in "SchwefeL" Erg.-Bd.2, 1978, pp. 126/7, and the papers [1 to 3]. For the vaLence force constants (f) the designations from [4] are used beLow. The symmetry force constants (F) are reLated to the f as described in [2, 4], see aLso [5]. Another sign convention for F34 is used in [1]. The foLLowing tabLe shows two compLete sets of symmetry force constants. The first set is derived from the observed fundamentaL frequencies Vi of the isotopic species 92MoFs and lOOMoFs [5]. The second set is based on onLy the isotopicaLLy unresoLved MoFs frequencies [3] and on the Fadini method of the "next soLution" [6] (see aLso [7]) for the three constants of the F1u symmetry bLock [8] (F ij in mdyn/A): F34 remark Ref. 6.16 4.76 4.65 0.25 0.25 0.28 0.08 a) [5] 6.14 4.64 4.33 0.02 0.25 0.29 0.08 b) [8] a) No error Limits are given because the harmonic frequencies were not avaiLabLe. These wouLd raise F11 , F22, and F33 by a few percent. The aLternative soLution for the ambiguous F1u constants, F33 = 1.19, F34 = 1.12, F44 = 1.98 mdyn/A was rejected in view of a comparison of experimentaL (see p. 135) and caLcuLated vibrationaL ampLitudes [5]. b) F34 = - 0.02 in the originaL paper [8] is due to an opposite sign convention. Frequencies Vi from [3]. F34 = 0.250 ± 0.004 mdyn/A was derived in [9] from the V3 isotopic shift measured by [10]. F34 =0.257 ±0.047 and 0.203 ±0.176 mdyn/A were obtained from the isotopic shifts of V3 and V4, respectiveLy (weighted average: F34 = 0.253 ± 0.045 mdyn/A) [5]. F34 =0.19 rndyn/A resuLted for a V3 shift caLcuLated by a semi-empiricaL formuLa (from data of [5]) [9]. Fij vaLues which, except for F66 = 0.2766, were simiLar to those tabulated above were derived from the measured Vi [5] and CorioLis coupLing constants ~ (presumabLy the theoreticaL ~ vaLues from [5] were used) [11]. The three force constants of the F1u bLock (F33 , F34 , F44) are to be determined from onLy two frequencies (V3, V4). In order to remove the impLied ambiguity, different constraints were imposed on the set of force constants and yieLded the foLLowing range of resuLts: Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 139 V3' V4 in cm-1 constraint F33 F34 F44 remark Ref. 749.5, 265.7 [5) L34 =O 4.585 0.143 0.252 [12) L-F approximation 4.52 0.14 0.25 a) [13) PED 4.504 0.072 0.252 b) [12) c) 741, 262 [3) F44 =min. 4.634 0.144 0.246 [14) d) F34/F 44 = 4mF/(m MO + 2mF) 4.480 0.139 0.245 [15) a) The L-F method [16) negLects the squares of the L-matrix eLement L34 and of F34• b) PED = potentiaL energy distribution, see [17). c) Method equivaLent to L34 = 0, see [17). d) The constraint used corresponds to fuu-fuu'= min. with respect to fru-fra, [3). F34 sign convention from [1) was used in [15). The F1u force constants in [18, 19) show stronger deviations from those given above. The F1u constants were aLso determined using the concept of "atomic force constants" [20), or a Linear transformation between normaL and symmetry coordinates [21). or modeLs based on the Urey BradLey or the generaL vaLence force fieLds [22). Outdated frequency sets were used in [23, 24). VaLence force constants (or combinations; aLL in mdyn/A) are given in the foLLowing tabLe. The first set is based on measured frequencies of 92MoF6 and 1OOMoF6 [5). The second and the third set are based onLy on six (isotopicaLLy unresoLved) vibration modes. They make use of additionaL constraints (see the remarks): fr 'rr 'rr' fru -fra' fu-fuu'" fuu -fuu' fuu,-fuu'" remark Ref. 4.94 0.23 0.29 0.13 0.16 0.04 -0.06 a) [5) 4.87 0.23 0.35 0.07 0.16 (0.04) -0.06 b) [13) 4.843 0.255 0.328 0.070 1.165 0.041 -0.054 c) [3) a) fr may be a few percent higher if harmonic frequencies were used. The other constants, however, might change by up to ± 0.01 mdyn/A. The originaL paper gives fu-fuu' = 0.22 [5). b) 92MoF6 frequencies [5) and the L-F approximation [16) (see above) were used. The originaL paper gives fu-fuu' = 0.22 and fuu -fuu,=0.44 [13). c) Their own set of revised MoF6 frequencies and the condition F34/F 44 = 4 mF/(m MO + 2mF) were used [3). Constants of the generaL vaLence force fieLd were caLcuLated by various constraints or approximations [18, 19,25 to 29) (another caLcuLation using the L-F approximation is in [30)). For simpLified or outdated sets of constants see [1, 2, 24, 31 to 41). Urey-BradLey type force fieLds were aLso given in [30, 35, 36, 41 to 43). References: [1) Pistorius, C. W. F. T. (J. Chem. Phys. 29 [1958)1328/32). [2) CLaassen, H. H. (J. Chem. Phys. 30 [1959) 968/72). [3) Weinstock, B.; Goodman, G. L. (Advan. Chem. Phys. 9 [1965) 169/319, 199, 309/12). [4) McDoweLL, R. S.; HoLLand, R. F.; McCuLLa, W. H.; Anderson, G. K.; Reisfeld, M. J. (J. Mol. Struct. 145 [1986) 243/56, 251). [5) McDoweLL, R. S.; Sherman, R. J.; Asprey, L. B.; Kennedy, R. C. (J. Chem. Phys. 62 [1975) 3974/8). [6) Fadini, A. (Z. Naturforsch. 218 [1966) 426/30). [7) Peacock, C. J.; MüLLer, A. (Z. Naturforsch. 238 [1968)1029/33). Gmelin Handbook Mo Suppl. Vol. B 5 140 Molybdenurn Fluorides [8] Müller, A.; Fadini, A.; Peacock, C. (Z. Physik. Chern. [Leipzig] 238 [1968]17/21). [9] McDowell, R. S. (Spectrochirn. Acta A 42 [1986]1053/7). [10] Curnrnings, J. C. (J. Mol. Spectrosc. 83 [1980] 417/30, 427). [11] Chinnappan, V. A.; Natarajan, A. (Prarnana 18 [1982]501/9; C.A. 97 [1982] No. 225850). [12] Sarkar, P. C.; Singh, G. C. (Spectrosc. Letters 11 [1978]17/31,27). [13] Verrna, U. P.; Sharrna, D. K.; Pandey, A. N. (Acta Ciencia Indica 3 [1977] 58/62; C.A. 87 [1977] No. 159286). [14] Thakur, S. N.; Rao, D. V. R. A.; Rai, D. K. (Indian J. Pure Appl. Phys. 8 [1970]196/8). [15] Cyvin, S. J.; Cyvin, B. N.; Brunvoll, J.; Andersen, B.; St0levik, R. (SeLec. Top. Struct. Chern. 196769/89, 77). [16] Pandey, A. N.; Sharrna, D. K.; Verrna, U. P.; Arora, L. D.; Gupta, S. L.; Singh, B. P. (Indian J. Pure Appl. Phys. 14 [1976] 815/8). [17] Becher, H. J.; Ballein, K. (Z. Physik. Chern. [Frankfurt] 54 [1967] 302/18, 310). [18] Nagarajan, G.; BrinkLey, D. C. (Monatsh. Chern. 104 [1973]1183/202, 1193/4). [19] Nagarajan, G.; Adarns, T. S. (Z. Physik. Chern. [Leipzig] 255 [1974] 869/88, 875). [20] Rao, K. R. P.; Dash, P. C.; Mishra, K. C.; Mohanty, B. S. (Indian J. Pure Appl. Phys. 16 [1978] 10517). [21] Thyagarajan, G.; Subhedar, M. K. (Indian J. Pure Appl. Phys. 12 [1974] 309/11). [22] Knyazev, D. A.; lvLev, A. A.; Popov, I. B. (Zh. Fiz. Khirn. 43 [1969]1269/78; Russ. J. Phys. Chern.43 [1969] 704/8). [23] Meisingseth, E.; Brunvoll, J.; Cyvin, S. J. (Kgl. Norske Videnskab. SeLskabs Skrifter 1964/65 No. 7, pp. 1/49, 45). [24] Nagarajan, G. (BuLI. Soc. Chirn. BeLges 72 [1963] 276/85). [25] Awasthi, M. N.; Mehta, M. L. (Spectrosc. Letters 2 [1969] 327/31). [26] Keng, Fang Ting [Quyen, Phan Dinh]; Kovrikov, A. B. (Zh. Prikl. Spektrosk. 15 [1971]81/5; J. Appl. Spectrosc. [USSR]15 [1971] 899/902). [27] Uendling [Wendling], E.; Makhrnudi [Mahrnoudi], S. (Opt. Spektroskopiya 32 [1972] 492/500; Opt. Spectrosc. [USSR] 32 [1972] 257/61). [28] Sabapathy, K.; Rarnasarny, R. (Indian J. Phys. B 58 [1984] 464/72). [29] Kochikov, I. V.; Yagola, A. G.; Kurarnshina, G. M.; Kovba, V. M.; Pentin, Yu. A. (Spectro chirn. Acta A 41 [1985] 185/9). [30] Pandey, A. N.; Sharrna, D. K.; Verrna, U. P. (Acta Phys. Polon. A 51 [1977]475/85,480). [31] Linnett, J. W.; Sirnpson, C. J. S. M. (Trans. Faraday Soc. 55 [1959] 857/66). [32] Nagarajan, G. (Australian J. Chern. 16 [1963] 906/7). [33] Kirnura, M.; Kirnura, K. (J. Mol. Spectrosc. 11 [1963] 368/77, 375). [34] Singh, R. B.; Rai, D. K. (Can. J. Phys. 43 [1965]167/9). [35] Califano, S. (Atti Accad. NazI. Lincei Classe Sci. Fis. Mat. Nat. Rend. [8]25 [1958]284/91). [36] LabonviLle, P.; Ferraro, J. R.; Wall, M. C.; Basile, L. J. (Coord. Chern. Rev. 7 [1971/72] 257/87, 265). [37] VenkateswarLu, K.; Sundararn, S. (Z. Physik. Chern. [Frankfurt] 9 [1956]174/9). [38] Gaunt, J. (Trans. Faraday Soc. 50 [1954] 546/51). [39] Tanner, K. N.; Duncan, A. B. F. (J. Arn. Chern. Soc. 73 [1951]1164/7). [40] Heath, D. F.; Linnett, J. W. (Trans. Faraday Soc. 44 [1948] 873/8, 45 [1949] 264/71). [41] Kirn, H.; Souder, P. A.; CLaassen, H. H. (J. Mol. Spectrosc. 26 [1968] 46/66, 52). [42] Hiraishi, J.; Nakagawa, 1.; Shirnanouchi, T. (Spectrochirn. Acta 20 [1964] 819/28, 824). [43] Thakur, S. N.; Rai, D. K. (J. Mol. Spectrosc. 19 [1966] 341/8). Gmelin Handbook Mo Suppl. Vol. B 5 141 2.2.8.2.12 Bond Disscociation Energy D(FsMo-F) and Average Bond Energy ReLiabLe D vaLues (in kJ/moL) were derived from a combination of formation enthaLpies ß Hf (in kJ/moL) taken from the Literature for MoFs and Fand measured vaLues for gaseous MoFs [1 to 3]. Recent ßHf data given in [4] wh ich incLude the MoFs resuLts of [1,2] suggest D = 392.0 ± 5.4 and 395.7 ± 5.4 at T = 0 and 298 K, respectiveLy (the D vaLues are not given in the paper [4]). In agreement with the previousLy reported D298 = 393 [1], D298 = 396 ± 5 given as Rx(47600±600 K) was derived from -ßHf(MoFs)=1241 ±4 given as Rx(149300±500 K) at 298 K [2] and oLder ß Hf vaLues of MoFs and F from [5]. Do = 385.2 foLLowed from ß Hf(MoFs) = -1243.2 at 0 K [3] and corresponding ß Hf data for MoFs and F from [5]. D298 = 397.1 ± 2.5 was cited as "from the Literature" in [6]. D = 394 was earLier estimated [7] from the beginning of the continuous UV absorption by MoFs at 281.5 nm C~424.3 kJ/moL) [8] (see p.160). The average bond energy 444.8 kJ/moL is obtained as one-sixth of the MoFs atomization enthaLpy ßH~t (0 K)=2669 kJ/moL [4]; aLso see [1]. SimiLar vaLues were 447.7 (given as R x 53900 K in the text and R x 53800 Kin the abstract of the paper) [2],449 [9], and 449.4 kJ/ moL [10]. The higher vaLues 455.6 [11, 12] or 454 kJ/moL cited in [7] are mainLy due to an outdated MoFs formation enthaLpy (- 382 kcaVmoL or -1598 kJ/moL, see p. 155). References: [1] HiLdenbrand, D. L. (J. Chem. Phys. 65 [1976]614/8; NucL. Instrum. Methods 186 [1981] 357/63). [2] KLeinschmidt, P. D.; Lau, K. H.; Hildenbrand, D. L. (J. Chem. Thermodyn.11 [1979]765/72). [3] Borshchevskii, A. Ya.; Sidorov, L. N.; BoLtaLina, O. V. (DokL. Akad. Nauk SSSR 285 [1985] 377/81; DokL. Phys. Chem. Proc. Acad. Sci. USSR 280/285 [1985] 1109/12). [4] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonaLd, R. A.; Syverud, A. N. (JANAF ThermochemicaL Tables, 3rd Ed., Pt. 11, MidLand, Mich., 1985/86, p. 1162). [5] StuLL, D. R.; Prophet, H. (JANAF ThermochemicaL TabLes, 2nd Ed., NSRDS-NBS-37 [1971]). [6] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982]145/56, 150). [7] Chester, A. N.; Hess, L. D. (IEEE J. Quantum Electron. 8 [1972]1/13, 12 footnote). [8] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951]1164/7). [9] Burgess, J.; Haigh, 1.; Peacock, R. D. (J. Chem. Soc. DaLton Trans. 1974 1062/4). [10] BartLett, N. (Angew. Chem. 80 [1968] 453/60; Angew. Chem. Intern. Ed. EngL. 7 [1968] 433/9). [11] MetyeL, A. S.; Nastyukha, A.1. (Proc. 13th Intern. Co nt. Phenom.loniz. Gases, Berlin, FRG, [1977], VoL. 1, pp. 379/80; C. A. 89 [1978] No. 121531). [12] Drobot, D. V.; Pisarev, E. A. (Zh. Neorgan. Khim. 26 [1981]3/16; Russ. J. Inorg. Chem. 26 . [1981]1/8). 2.2.8.2.13 Intermolecular Potential Parameters for the isotropie part qJ(r) of the intermoLecuLar potentiaL were derived from the temperature dependence of the second vi riaL coefficient B (see p. 149) and trom the viscosity T) of gaseous MoFs (see p. 146). A (generaLized) Lennard-Jones (L-J)-(n,6) potentiaL, qJ = E[6 (rmin/r)n- n(rmin/r)S]/(n - 6), and the more famiLiar L-J-(12,6) potentiaL, in the form qJ = 4E[(rolr)12 - (rolr)S], and a (modified) Buckingham (B)-(exp,6) potentiaL, see [1], were used. The L-J-(12,6) potentiaL was aLso repLaced bya Kihara (K) potentiaL, where r stands for the distance Gmelin Handbook Mo Suppt. Vot. B 5 142 MoLybdenum FLuorides between the surfaces (instead of the centers) of the two moLecuLes (see [2]). Parameters n, E (depth of the potentiaL), and IQ (distance at which L-J-(n,6) 18 513 K 5.57 B(T) [3] a) b) L-J-(12,6) (12) 434 K 4.96 (5.78) f] [4] 230 K 7.6 B(T) [5,6] B-(exp,6) 481 K 5.47 f] [4] [1] K-(12,6) (12) 1130 K 1.7 B(T) [5] [6] c) a) E= 7.08 xlO-14 erg. - b) rminaccording to [3]. PreviousLy: Elk= 223 K, ro=5.820 A [7]. See aLso a more detaiLed report [8] on f] and on B(T). - c) See aLso [9]. Information on the anisotropie part of the intermoLecuLar potentiaL was obtained from the 19F spin-Lattice reLaxation time of the pure gas (see p. 127), using for the isotropic part a hard sphere, an L-J-(12,6), and a B-(exp,6) potentiaL [1]. References: [1] Ursu, 1.; Bogdan, M.; BaLibanu, F.; Fitori, P.; MihaiLescu, G.; Demco, D. E. (Mol. Phys. 60 [1987]1357/66, 1362, 1365). [2] Kihara, T. (Progr. Theor. Phys. [Kyoto] Suppl. No. 40 [1967] 177/206, 178). [3] Heintz, A.; LichtenthaLer, R. N. (Ber. Bunsenges. Physik. Chem. 80 [1976] 962/5). [4] Morizot, P.; Ostorero, J.; PLurien, P. (J. Chim. Phys. 70 [1973]1582/6). [5] MaLyshev, V. V. (TepLofiz. Vys. Temp.12 [1974]743/8; High Temp. [USSR]12 [1974]649/53). [6] MaLyshev, V. V. (TepLofiz. Vys. Temp.12 [1974]1114/8; High Temp. [USSR]12 [1974]979/83). [7] Ostorero, J. (CEA-N-1293 [1970]1/36; N.SA 24 [1970] No. 36195). [8] Morizot, P. (CEA-R-4380 [1973]1/118; C.A. 79 [1973] No. 83607). [9] MaLyshev, V. V. (TepLofiz. Svoistva Gazov 1976 97/105; Ref. Zh. Khim. 1977 No. 2B 771). 2.2.8.2.14 Mass Spectra The mass spectrum of MoF6 in an Ni ceLL at 30°C (acceLerating voLtage not given) is as foLLows [1]: ion ...... MoFt MoFt MoFt MoF~ MoF+ Mo+ intensity ...... 100 32 19 15 11 8 From ionization efficiency curves plotted in [2]. the foLLowing appearance potentiaLs (AP) have been evaLuated (Ar reference gas: Ar+ at 15.75 eV) [2]: ion ...... MoFt MoFt MoFt MoF~ MoF+ Mo+ AP in eV ...... 16 19.5 23.5 29.5 35.5 41.0 For the abundant MoFt and the Less abundant MoFt the AP=15.2±0.2 and 19 eV, respectiveLy. Lower appearance threshoLds given in the paper refer to the ionization of reaction products formed in the MoF6-Mo and SF6-Mo systems or refer to the fragmentation of MoOF4 (but not to the fragmentation of MoF6) [3]. The fragmentation reaction yieLding MoFt was formuLated as MoF6+e-~MoFt+F+2e- (AP=15.2±0.3 eV) [4]. Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 143 References: [1] StrehLow, R. A.; Redman, J. D. (ORNL-4254 [1968]134/6; N.SA 22 [1968] No. 47112). [2] Weaver, e. F.; Redman, J. D. (ORNL-4449 [1970]116/21,117/8; N.S.A. 24 [1970] No. 18587). [3] HiLdenbrand, D. L. (J. ehem. Phys. 65 [1976] 614/8). [4] KLeinschmidt, P. 0.; Lau, K. H.; HiLdenbrand, D. L. (J. ehem. Thermodyn.11 [1979]765/72). 2.2.8.3 Crystallographic Properties Polymorphism. MoFs has an orthorhombic Low-temperature modification beLow about -10oe and a cubic high-temperature modification above this temperature up to the meLting point (-17°C). This behavior is simiLar to other transition metaL hexafluorides (see, e.g., [1]). Perhaps another phase transition occurs near -54°e. Under the vapor pressu re of MoFs, the orthorhombic-cubic transition occu rs at 263.479 ± 0.02 K (tripLe point) as determined by heat capacity measurements [2], and 263.6 K were found by [3]. Vapor pressure measurements indicate 262.89 ± 0.14 Kat 94.1 Torr [4] or -8.7°e (264.4 K) and 104.7 Torr [5]. Under p=1 atm (MoFs pLus He), the transition occurs at 263.50±0.02 Kin the heat capacity study [2]. By DTA and visuaL inspection, transitions at -8.9 ± 0.9°e (264.2 K) [6], -9.6°e (263.6 K) [7], -10.5°e (262.6 K) [8], and -10.6°e (262.6 K) [9] were found. ThermaL anaLysis (TA) showed arrests at -10.8±0.1°e and at -9.8±0.05°e (262.4 and 263.4 K) on cooLing and heating, respectiveLy [10]. This tendency for the high-temperature (cubic) modifi cation to supercool [10] was aLso noted by [3]. The transition was pLaced at -9.6°e (263.6 K) in the X-ray diffraction study [1]. The solid-solid transition is refLected in the 19F NMR spectra by a jump at -8.7°e (264.4 K) in the LongitudinaL reLaxation time 1; [11]. At the transition tempera ture, given as -10oe (263 K), the narrow 19F NMR resonance from the cubic modification is superimposed (nearLy centered) on the broad resonance from the orthorhombic modification [12]. The soLid-soLid transition is pLaced at 263.5 K in the review [13]. The heat capacity study indicates an enthaLpy of transition öHtr = 1953.2 ± 2.0 caLlmoL (at the tripLe point, see above) [2] confirming the simiLar study which had reveaLed this transition by the detection of the associated ÖHtr =1957±10 caLlmoL at the tripLe point (263.6 K) [3]. öHtr =1960 caLlmoL [5] and 9.1 ±0.3 kJ/moL~2174.9 caLlmoL (at 262.89 ± 0.14 K and 94.1 Torr) [4] resuLt from the vapor pressure studies [4, 5]. Under 1 atm (MoFs pLus He), ÖHtr =1953.3± 2.0 caLlmoL (at 263.50±0.02 K) [2]; ÖHtr =8.171±0.008 kJ/moL (~1952.9 caLlmoL) [20]. The associated entropy of transition is ÖStr = 7.412 caL· moL-1. K-1 [2]. ÖStr = 7.40 caL· moL-1. K-1 are evaLuated in [5]. A strong change in the chemicaL shift was observed near -54°e in the 19F NMR and attributed to a phase change [12]. The low-temperature modification of MoFs, which is isomorphous with UFs (cf. "Uran" Erg. Bd. e 8, 1980, pp. 86/9), crystaLlizes with orthorhombic symmetry, space group Pnma-D~~ (No. 62); Z = 4 [14, 15]. The LaUice parameters (in A) at various temperatures T are determined from X-ray [1,10] and neutron powder diffraction data [14, 15] as foLlows: Tin K a b c Ref. 253 9.65±0.02 8.68±0.03 5.05±0.02 [10] 237 9.61 ±0.02 8.75±0.02 5.07±0.02 [1] 193 9.559(9) 8.668(8) 5.015(5) [14] 77 9.387(3) 8.530(3) 4.953(3) [15] GmeLin Handbook Mo SuppL. VoL. B 5 144 MoLybdenum Fluorides The structuraL investigation was performed by neutron powder diffraction at 193 and 77 K be cause the X-ray patterns were not suitabLe for detaiLed structuraL anaLysis and singLe crystaLs couLd not be isoLated. ProfiLe refinements gave R vaLues of 0.11 at 193 K [14], and 0.076 (B(Mo) = 0.69(21) and B(F)=1.90(15) A2) at 77 K [15]. Apowderdiagram at 193 K isdispLayed in [14], another at 77 Kin [15]. The observed and caLcuLated d vaLues from an X-ray diffraction powder diagram obtained at - 20°C are given by [10]. PositionaL parameters (X104) of orthorhombic MoFs at 193 and 77 K compared with the ideaL vaLues for a perfect hexagonaL cLose-packed structure are: atom position parametera) at 193 K [14] at 77 K [15] ideaL vaLue Mo 4c x 1224(12) 1285(11) 1250 z 1043(35) 912(26) 833 F(1 ) 4c x 155(14) 76(13) 0 z -1978(30) -2033(28) -2500 F(2) 4c x 2559(17) 2441(18) 2500 z 3744(71) 3933(59) 4167 F(3) 8d x 221 (11) 170(10) 0 Y 993(11 ) 993(10) 833 z 2446(20) 2423(16) 2500 F(4) 8d x 2320(10) 2375(10) 2500 Y 1120(21 ) 1047(21 ) 833 z -711(42) -706(35) -833 a) Nonstated y parameters are y = 0.25. The structure is based on hexagonaL cLose-packed fLuorine Layers stacked perpendicuLarLy to the x axis. The Layers at x = 0 and x = V4 at 193 Kare shown in Fig. 44. The F atoms are contracted around Mo atoms to form a nearLy reguLar octahedron whiLe the hexagonaL cLose packing around vacant octahedraL hoLes is expanded and greatLy distorted. The deviations from ideaLity are greater than in the case of UFs since MOVI is the smaLLer cation and shorter metaL-fLuorine bonds are formed [14]. On cooLing to 77 K the octahedra pack more efficientLy and the atomic coordinates more cLoseLy approach the ideaL coordinates [15]. Bonding distances (in A) at 193 Kare [14]: Mo-F(1) 1.827(17) Mo-F(3) 1.766(12) (2x) Mo-F(2) 1.861(29) Mo-F(4) 1.817(20) (2x) F-Mo-F angLes between neighboring F atoms vary between 82.3(15) and 95.4(10t, whiLe the angLes aLong the diameters of the octahedron are F(1 )-Mo-F(2) =170.7(17) and F(3)-Mo-F(4) = 173.0(12t (2x) [14]. At 77 K the mean Mo-F distance was found as 1.824(7) A. In contrast to the vaLues at 193 K, differences in the bond Lengths were not observabLe [15]. As the Mo-F distances are Less than the sums of the Mo and F ionic radii by about 0.10 A the structure is better described as an assembLage of interLocking MoFs moLecuLes rather than a cLose-packed ionic array [14, 15]. The orthorhombic modifications of MoFs, WFs, and UFs are compared in [15,16]. High-Temperature Modification. The X-ray powder diffraction pattern 01 this modi1ication can be indexed on the basis 01 a body-centered (bc) cubic structure [1, 10]. 19F NMR measure ments (see p. 148) estabLished the presence 01 a "pLastic" modi1ication with the octahedraL moLecuLes undergoing rapid rotationaL and sLow transLationaL motions, see, e. g. [5, 12, 17, 18]. The Lattice parameter was determined as a = 6.23 ± 0.04 Aat 5°C [1], 6.221 ± 0.005 Aat rc [19], GmeLin Handbook Mo Suppl. Vol. B 5 MoF6 145 and 6.23 ± 0.01 A at 1Q°C [10]; Z = 2 [1, 19]. The structure was determined by neutron powder diffraction at 266 K. As the MoF6 groups are in rapid rotational disorder, the pattern collected was analyzed by the method of Kubic Harmonics, where only cubic symmetry is assumed and no molecular model presupposed. The 4th order Kubic Harmonie model (Mo on 000 + bc) corresponds to a diffuse fluorine distribution, smeared out over the surface of a sphere, but with maxima along the fourfold axes. Profile refinement gave an Mo-F distance of 1.802(14) A; R=0.103 [19]. Fig. 44. The fluorine layers at x = 0 and x = V4 in MoF6 at 193 K illustrating the distortions from hexagonal close packing [14]. / / 'L------=jE----f(1) ---"L\ / _____ \~ / References: [1] Siegel, S.; Northrop, D. A. (Inorg. Chem. 5 [1966] 2187/8). [2] Osborne, D. W.; Schreiner, F.; Malm, J. G.; Selig, H.; Rochester, L. (J. Chem. Phys. 44 [1966] 2802/9, 2804). [3] Brady, A. P.; Myers, O. E.; Clauss, J. K. (J. Phys. Chem. 64 [1960]588/91); Brady, A. P.; Clauss, J. K.; Myers, O. E. (WADC-TR-56-4 [1955]1/55, 14; N.S.A. 10 [1956] No. 7512). [4] Meixner, D.; Heintz, A.; Lichtenthaler, R. N. (Ber. Bunsenges. Physik. Chem. 82 [1978]220/5). [5] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1563/8,1565). [6] Prusakov, V. N.; Korobtsev, V. P.; Markov, S. S.; Ezhov, V. K.; Khokhlov, V. A.; Bosenko, I. I. (Zh. Neorgan. Khim. 17 [1972] 2549/52; Russ. J. Inorg. Chem. 17 [1972] 1334/6). [7] Legasov, V. A.; Marinin, A. S. (Zh. Fiz. Khim. 46 [1972]2649/51; Russ. J. Phys. Chem. 46 [1972]1515/6). [8] Khaldoyanidi, K. A.; Yakovlev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981]3067/9; Russ. J. Inorg. Chem. 26 [1981]1639/40). [9] Popov, A. P.; Tsvetnikov, A. K.; Goncharuk, V. K. (Zh. Neorgan. Khim. 23 [1978] 236/9; Russ. J. Inorg. Chem. 23 [1978]132/3). [10] Trevorrow, L. E.; Steindler, M. J.; Steidl, D. V.; Savage, J. T. (U.S. At. Energy Comm. ANL-7240 [1966]1/20, 13/4, 16; C.A. 67 [1967] No. 57717; Advan. Chem. Sero No. 71 [1967] 308/l9, 314, 31617). [11] ,Blinc, R.; Lahajnar, G.; Pirkmajer, E.; Zupancic, I. (Proc. Colloq. AMPERE 14 [1966/67] 1068171); Blinc, R.; Pirkmajer, E.; Slivnik, J.; Zupancic, I. (J. Chem. Phys. 45 [1966] 1488/95, 1495). [12] Afanas'ev, M. L.; Gabuda, S. P.; Lundin, A. G.; Opalovskii, A. A.; Khaldoyanidi, K. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 4, pp. 18/22; C.A. 70 [1969] No. 52864). [13] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec.lssue No. 7 [1980]11/191,46/58). [14] Levy, J. H.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975] 398/401). [15] Levy, J. H.; Taylor, J. C.; Waugh, A. B. (J. Fluorine Chem. 23 [1983] 29/36). [16] Lew, J. H.; Taylor, J. C.; Wilson, P. W. (J. Sqlid State Chem. 15 [1975] 360/5). [17] Virlet, J.; Rigny, P. (Compt. Rend. B 267 [1968] 1238/40). Gmelin Handbook Mo Su ppl. Vol. B 5 10 146 Molybdenum Fluorides [18] Rigny, P.; Virlet, J. (J. Chem. Phys. 51 [1969] 3807/16, 3809). [19] Levy, J. H.; Sanger, P. L.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975]1065/7). [20] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. (JANAF Thermochemical Tables, 3rd Ed., Pt. 11 [1985] 1161). 2.2.8.4 Mechanical and Thermal Properties 2.2.8.4.1 Mechanical Properties Density D in g/cm3 The density D of orthorhombic MoFs is given by D=3.619-0.0013 T, T in K [1]. It was determined by the displacement (He Dis) [1], by neutron diffraction (ND) [2], and by X-ray diffraction (XD) [3]: D ...... 3.519 3.393 3.35 3.27±0.03 Tin K ...... 77.16 173.83 196 -237 (-36°C) method ...... He Dis He Dis ND XD Ref...... [1] [1] [2] [3] The density of cubic MoFs has been determined by X-ray diffraction. The Dx values are 2.895 at 266 K [4] and 2.88 at +5 [3] and +10°C [8]. The laUer Dx value has been cited with an uncer tainty of ± 0.04 in [1] (note that actually the laUice parameter was given as a = 6.23 ± 0.04 A in [3]). From weight and volume measurements, Dm = 2.88 and 2.91 at 0 and +8°C, respectively [8,9]. The density of liquid MoFs was determined by pycnometry as D = 2.544,2.491, and 2.341 at T = 294.33,307.08, and 344.63 K, respectively [1]. At the normal boiling point, D = 2.47 [5]; also see [6] (T not given). In the experimentally studied range 17 to 76.rC (which exceeds the boiling point), the density is given by D=2.614-0.00416t, tin °c [5]. Along the liquid-vapor equilibrium line, the D of the liquid ranges from 2.285 at 350.9 K to 1.099 at 483.7 ± 0.4 K. D is weil approximated bya polynomial in T'!J (up to T'!J). At the critical point (485.2 ±1.0 K and 49.7 ±0.6 bar), Dc,=0.916±0.008 [7]. Calculated Dc,=0.93 [5]. The density of the saturated vapor ranges from D = 0.005001 at 291.6 K to 0.698 at 484.8 ± 0.6 K and is weil approximated bya polynomial in T'/4 (up to T'/4). For vapor densities between D=0.0013 and 2.28, see this compressibility study wh ich covers temperature and pressure ranges 280 to 590 K and -0.13 to 246 bar [7]. For the normal boiling point, D = 0.008 g/cm3 was calculated [5]. Viscosity The temperature dependence of the viscosity l] was determined for liquid MoFs between 17 and 60°C. With l] in cP and T in K, log l]=-1.542+431.7/T. At the normal boiling point, l] = 0.71 cP [5]. The viscosity of gaseous MoFs was measured by application of the Hagen-Poiseuille law. The apparatus used was calibrated with N2 [10]. The l] was measured at pressures between 20 and 100 Torr and temperatures ranging from 40 to 140°C [11]. The smoothened data of [10] indicate a linear T dependence: l] in f-tP 150 158 160.0,162.5 163.8,165.5 165.8,168.8 167 170.3,172.9 tin °c 40 60 66 74.2 81.2 80 91.1 Ref...... [11] [11] [10] [10] [10] [11] [10] Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 147 l] in flP 174.8, 175.8 176 176.2, 178.0 184 184.1,184.3 192 191.0,193.5 tin °C 100 100 103.9 120 120.5 140 140.3 Ref...... [10) [11) [10) [11) [10) [11) [10) The l] value 170 flP was ealeulated for the vapor at the normal boiling point [5). Surface Tension From 17 to 60°C, the surfaee tension 0 (in erg/em 2) deereases linearly with temperature t (inOC): 0=19.7-0.105 t. At the normal boiling point, 0=17.9 erg/em 2 [5). Dynamics of Condensed MoF6• Diffusion Orthorhombic MoF6• In the early NMR study [14), two temperature regimes were distin guished: "MoFslII" below about -60°C and "MoFslI" up to -10°C. The seeond moment of the 19F NMR line width (extrapolated to H = 0) is 6.65 ± 0.7 and 0.90 ± 0.05 Oe2 in MoFs 111 and MoFs 11 eorresponding to rigid laUiee behavior and isotropie rotations, respeetively. The change in the ehemieal shift öC 9F) is small at the eubie MoFs I to MoFs 11 phase transition, but below -54°C the NMR speetra show two eomponents with intensity ratio 2: 1 aUributed to 4 short and 2 long Mo-F bonds [14); see also the change from symmetrie to asymmetrie line shape noted on eooling in [15). The MoFs moleeules are distorted in the orthorhombie modifieation and librate about their equilibrium positions. After the lapse of some time, the moleeules make a rotational jump and redistort themselves, the axial and equatorial F positions being fixed laUiee sites [15). The inerease in the seeond moment by a faetor of 3 to 5 on eooling indieates a gradual freezing-in of the rotational degree of freedom [16), the value of - 5 Oe 2 (for H ~ 0) indieating rigid laUiee behavior at low temperatures [17) (also see above [14)). On the other hand, elose to the orthorhombie-eubie transition, the MoFs moleeules rotate at least about a C3 axis of the (idealized) oetahedra as dedueed from the frequeney-independent, roughly Gaussian line shape of the 19F NMR signals [15). Above -90°C, the reorientations oeeur with apparently equal probability about eaeh of the C3 axes of the (idealized) oetahedra [18). Free rotation about the fourfold axes is assumed for the range -40 to -10°C in [14). The longitudinal relaxation time Tl was studied between -123 and - 286 K. Up to -175 K, 1, is large and temperature-independent. Then, up to - 250 K, Tl deereases exponentially due to moleeular motions (elose to rotations) aetivated by EA = 0.38 eV [17). EA = 0.33 eV was evaluated for the moleeular rotations below - 250 K from Arrhenius plots of the ratio T/T, measured between - 221 and - 261 K (Tz and T, are the relaxation times, longitudinal and in the rotating frame, respeetively, measured by slow passage through the 19F NMR at 8 MHz) [19); also, see [20, pp. 40/1). Arrhenius plots of 1, (for v = 9.2, 15.2, and 22.9 MHz) indieate EA = 0.48 eV for the moleeular reorientation (hindered rotations whieh modulate the intra moleeular dipolar interaetions) [16). Between about -10 and -142°C, EA =0.495±0.005eV [21), also see [18). Above -250 K, the lifetime 1: of a partieular eonfiguration is shorter than -0.02 f!S (1:·2n·8 MHz=1) as eoneluded from the temperature indepenee of T/T, (for T~250 K, v=8MHz) [19). On the other hand, below -90°C, no motional narrowing was observed and the eorrelation time 1: exceeds the transversal relaxation time T2. Below -90°C, the librating moleeules show small but frequent fluetuations [18). However, the MoFs mole eules are said to move independently, sinee jumps are rare events in orthorhombie MoFs [19). At the eubie to orthorhombie transition, the eorrelation time 1:J for the angular momentum of the MoF6 moleeules is 0.4 ps [24). Gmelin Handbook Mo Suppl. Vol. B 5 10' 148 Molybdenum Fluorides At the cubic to orthorhombic transition, 11 jumps to much lower values (by 1 to 2 orders of magnitude). This decrease is attributed to the strong compression of the lattice associated with the phase transition. For the activation energy EA determined from Arrhenius plots of 11 the result EA(orthorhombic) =0.38 eV>3EA(cubic) is given in [17). Cubic MoF6 has been studied rather extensively by NMR. This interest largely stems from the fact that it behaves like a liquid with respect to 19F NMR (there is a sharp, single 19F NMR line accompanied by satellites) and also shows a low entropy of fusion, see p. 150. In addition, when stored for a considerable time below the melting point, this modification tends to form a glass-clear mass (single crystal?). These characteristics suggest that this modification is a "plastic phase" [12). For the term "plastic phase" and properties characteristic of "plastic crystals", see, e.g. [13). The 19F NMR spectra of cubic MoFs do not differ much from those of liquid MoFs and the change in the chemical shift öC9F) is minute at the liquid to solid transition [14). An evaluation of 19F NMR relaxation data in [20) in terms of the theory by [22) yields a "glass transition" temperature of 13.5°C and a free volume ratio of 13% [20). The Lorentzian line shape of the 19F NMR lines indicates that the molecules perform diffusive translations much as in a viscous liquid [15, 23). The zero value of the second moment of the 19F NMR line width (H extrapolated to zero) indicates self-diffusion plus isotropic rotation for the molecules [14). Their motion consists of rapid (frequent) reorientations and slow (rare) translations [21); also see [15). At the melting point (17.4°C), the diffusion coefficient D = 0.52 X 10-8 cm2/s [15) correspond ing to a correlation time (inverse jump rate) T=0.07 f.IS [15, 21, 23). At the cubic to ortho rhombic transition T = 0.9 f.IS [15, 21, 24). Arrhenius plots of T indicate an activation energy of EA= 0.55 [21) (0.56 [23). 0.56 ± 0.01 [15)) eV. Liquid MoF6• From 20 to 78°C, the diffusion coefficient D (in 10-5 cm2/s) increases from 2.8 to 7.7. The D values were determined in a field with strong, known field gradient by the C9F) nuclear spin echo method. D = (0.0314 cm2/s)· exp (- Etransl/kT). The Elransl value of 0.11 eV given in the paper [25) (also see [20)) is obviously erroneous (a value of -0.18 eV would be more consistent with the Arrhenius plot of D and the table of D values given in [25)). The longitudinal relaxation time 11 measured between 18 and 84°C by adiabatic passage follows the Arrhenius law 11 =11 .. ·exp(Ero/kT) with 11 .. = 76 ms and Erot = 70 meV. At 70°C, the mean angular momentum of the MoFs molecules corresponds to a rotation through -55° per rotational jump. This angle increases by -12° for an increase in temperature by -50 K. These figures show that the molecules in liquid MoFs neither rotate freely nor is their motion adequately described by rotational diffusion (for the latter the amplitudes are too large) [25); also see [20). The frequency independent 11 of MoFs (at 23°C) suggests reservat ions with respect to a description of the MoFs molecular motion in terms of classical Brownian motion [26). References: [1) Osborne, D. W.; Schreiner, F.; Malm, J. G.; Selig,'H.; Rochester, L. (J. Chem. Phys. 44 [1966) 2802/9). [2) Levy, J. H.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975) 398/401). [3) Siegel, S.; Northrop, D. A. (Inorg. Chem. 5 [1966) 2187/8). [4) Levy, J. H.; Sanger, P. L.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975)1065/7). [5) Nisel'son, L. A.; Nikolaev, R. K.; Sokolova, T. D.; Stolyarov, V. 1.; Korolev, Yu. M. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 1, pp. 109/14; C.A. 69 [1968) No. 69834). [6) Isakov, V. P. (Zh. Fiz. Khim. 47 [1973) 702/4; Russ. J. Phys. Chem. 47 [1973) 395/6). Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 149 [7] Malyshev, V. V. (Teplofiz. Vys. Temp.12 [1974]743/8; High Temp. [USSR]12 [1974]649/53). [8] Trevorrow, L. E.; Steindler, M. J.; Steidl, D. V. (Advan. Chem. Sero No. 71 [1967] 308/19). [9] Trevorrow, L. E.; Steindler, M. J.; Steidl, D. V.; Savage, J. T. (U.S. At. Energy Comm. ANL- 7240 [1966] 1/20, 15; N.S.A. 21 [1967] No. 5828). [10] Ostorero, J. (CEA-N-1293 [1970]1/35; N.S.A. 24 [1970] No. 36195). [11] Morizot, P.; Ostorero, J.; Plurien, P. (J. Ctlim. Phys. 70 [1973]1582/6). [12] Cady, G. H.; Hargreaves, G. 8. (J. Chem. Soc. 1961 1563/8). [13] Proc. Symp. Plastic Cryst. Rotation Solid State, Oxford 1960, Phys. Chem. Solids 18 [1961] 1/92. [14] Afanas'ev, M. L.; Gabuda, S. P.; Lundin, A. G.; Opalovskii, A. A.; Khaldoyanidi, K. A. (Izv. Sibirsk. Otd. Akad. NaukSer. Khim. Nauk 1968 No. 4, pp. 18/22; C.A. 70 [1969] No. 52864). [15] Rigny, P.; Virlet, J. (J. Chem. Phys. 51 [1969] 3807/16). [16] 8linc, R.; Lahajnar, G. (Fizika [Zagreb]1 [1968]17/29; C.A. 70 [1969] No. 72747). [17] 8linc, R.; Pirkmajer, E.; Slivnik, J.; Zupancic, I. (J. Chem. Phys. 45 [1966]1488/95). [18] Virlet, J.; Rigny, P. (Chem. Phys. Letters 4 [1969170] 501/4). [19] Rigny, P. (Compt. Rend. 8265 [1967]1058/61). [20] Rigny, P. (CEA-R-3464 [1969]1/84; C.A. 71 [1969] No. 86416). [21] Virlet, J. (CEA-R-4344 [1973]1/164; C.A. 80 [1974] No. 76378). [22] Cohen, M. H.; TurnbuU, D. (J. Chem. Phys. 31 [1959] 1164/9). [23] Virlet, J.; Rigny, P. (Compt. Rend. 8 267 [1968] 1238/40). [24] Rigny, P.; Drifford, M.; Virlet, J. (J. Phys. CoUoq. [Paris] 32 [1971] C5a-229/C5a-232). [25] Rigny, P.; Virlet, J. (J. Chem. Phys. 47 [1967] 4645/52). [26] Rigny, P.; Demortier, A. (Compt. Rend. 8263 [1966]1408/10). 2.2.8.4.2 Thermal Properties Second Virial Coefficient The second virial coefficient 8(T) was determined for MoF6 at 15 temperatures in the range 320 to 460.9 K by comparison with the values for N2 [1] (for the method used, see [6]). At 320.0 and 460.9 K, 8(T) = -713 and -389 cm3/mol, respectively [1]. The 8 vS. T curve measured by [1] slopes less steeply than do the data of [2, 3] who determined 8(T) at 20 K intervals between 40°C (-790 cm3/mol) and 180°C (-320 cm 3/mol). The numericaUy identical results of [2,3] have been derived from viscosity data in [2] and by a volumetric and by a dielectric method in [3]. At 298.15 K, 8 = -923 ± 32 cm3 [5]. Considerably different values have been found by [4J. The 25 tabulated entries range from -4.94 cm 3/g at 300.5 K to -0.77 cm3/g at 593.2 K (corresponding to -;-1037 and -161.7 cm3/mol) [4]. Melting. Boiling. Vaporization Melting Point. Under its own vapor pressure, MoF6 fuses at 290.73 ± 0.02 K (tripIe point) according to the heat capacity study [5]; also see the 290.7 K of [7]. 290.73 ± 0.06 K were determined from temperature vs. time curves (both freezing and melting runs) byextrapolation to zero cryoscopic impurity conte nt [8, 9] and using the melting enthalpy value given in [5]. 290.95 ± 0.11 K and 409.6 Torr are given as tripIe point coordinates in the vapor pressure study [10]. 290.76 ± 0.02 K is given in the reviews [11 to 13J. 17.40°C and 398.1 Torr resulted from the vapor pressure study [14] and has later been confirmed (17.4 ± 0.09°C) [151. Thermal analysis indicates 17.4 ± OSC [16J. 17°C is given for the tri pIe point temperature in the NMR study [17]. Gmelin Handbook Mo Suppl. Vol. B 5 150 MoLybdenum Fluorides Under 1 atm (MoF6 pLus He), MoF6 meLts at 290.76 ± 0.02 K, see the heat capacity study [5]. SoLidification was found at 17°C [18]; aLso see [19]. A discontinuity in the NMR spectra occurs at 17.4°C [20]. 17.4°C is aLso given in [21,22], 17SC in [23], and 17.6°C in [24]. About 18°C is reported in the study of the MoF5-MoF6 phase diagram by DTA and visuaL inspection [25]; 18SC is given in the NMR study [26]. In the presence of smaU admixtures of HF the meLting point hardLy differs from that of pure MoF6 [27]. See aLso p. 181. SoiLing Point. See aLso under "Vapor Pressure" , p. 151. The boiLing point temperature Tb=34.0°C was determined in the vapor pressure study [14]. Other Tb vaLues (in 0c) are 33.8 [28],33.9 [24], 35.0 [23], 35 [18, 29, 30], and 36 [19]. At 2600 Torr, Tb=72.9°C [31 to 33]. The enthaLpies of fusion ~H~ =1034.2 and 1034.1, both ±1.0 caVmoL, have been determined by heat capacity measurements for fusion at 290.73 K (tripLe point TP) and at 290.76 K (normaL meLting point), respectiveLy [5]. Sy the same method, ~H~ =1059 ± 10 caVmoL(TP) [7]. Sy vapor pressure studies [10, 14], i. e., for TP, ~H~ = 915 caVmoL [14] (the 920 caVmoL given in a tabLe of [14] seems to be erroneous) and ~H~=4.4±0.1 kJ/moL [10]. The vaLue 4.3 kJ/moL is given in [24]. As a difference between the enthaLpies of subLimation and vaporization the very high vaLue 23.2 kJ/moL is given in [4]. ~H~ =1 034.1 caVmoL is recommended in the reviews [11,12]; ~H~/R = 520.4 ± 0.5 K according to [12]. ~H~ = 4.326 ± 0.004 kJ/moL C~ 1033.9 caVmoL) [13]. The Low vaLue for the entropy of fusion, ~S~ = 3.557 ± 0.004 caL' moL- 1 • K-1 (at 290.73 K), suggests that the high-temperature solid is a pLastic crystaL [5]. ~S~ = 3.15 caL· moL-l. K-l was evaLuated in the vapor pressure study [14]. ~S~/R=1.790±0.002 [12]. EnthaLpies of Sublimation and Vaporization. From the vapor pressure curve, the sublima tion and vaporization enthaLpies, ~HSUb and ~Hvap, have been derived by the CLausius CLapeyron relationship, see Fig.45 [10]. SimiLarLy, for the temperature range 40 to 88°C, ~Hvap=6607 caVmoL [32], and for the saturation pressure range ~2240 to ~2830 Torr, ~Hvap=6590 caVmoL [31] (6584 caVmoL [33]). For T=298.15 K, ~H~ap=6630±25 caVmoL resuLted from the heat capacity study [5], 6.66 kcaVmoL are given in [34] (see aLso [35]). According to the reviews [11, 12], ~H~ap.29a1R = 3367.4 ± 5 K [12] (3367 ± 10 K [11]) and ~H~ub.ofR=5617±5 K [12]. At the boiLing point, ~Hvap=27.8 kJ/moL (~6.64 kcaVmoL) [24]. 31 and 35 kJ/moL were estimated for vaporization and sublimation enthaLpies at 298 K by [36]. For cubic MoF6, ~HSUb = 5696.5 caVmoL was estimated from the difference between the heats of soLution of gaseous and cubic MoF6 in hexachLorobuta-1,3-diene [37]. 50r------~ o E ~ 40 1+lt' 1.... ortho - 1 Fig. 45. EnthaLpies of sublimation and :J 30 rhomblc cublc liquid vaporization, ~HSUb' ~Hvap, of MoF derived "'l +-++ + 6 . -+-+-+- from the vapor pressure vs. temperature [10]. 200 250 300 350 Temperature in K Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 151 The folLowing tabLes showenthalpies of sublimation and vaporization caLcuLated from the two-phase data of the vapor pressure study [4]: tlHsub in kJ/kg 156.4 157.9 155.7 Tin K ...... 282.0 286.0 289.0 tlHvap in kJ/kg 132.0 131.2 130.5 129.5 108.6 95.0 86.2 78.0 Tin K ...... 291.6 295.0 298.2 300.9 371.7 403.7 423.9 438.1 tlHvap in kJ/kg 70.3 63.0 56.4 49.8 37.5 26.2 14.8 Tin K ...... 448.4 457.4 463.6 468.8 477.8 482.5 484.8 Critical Point Parameters The criticaL point temperature, pressure, and density are Te, = 485.2 ± 1.0 K, Pe, = 49.7 ± 0.6 bar, and Oe,=0.916±0.008 g/cm3 according to the compressibiLity study [4]; aLso see [38]. By comparison with UF6, Ter was estimated at 215°C [17]. In a theoreticaL study, depending on the modeLs used, 1;,,=463 to 475 K, Pe,=42.9 to 52 atm, and Ve, (=0;;-,1)=1.01 to 1.171 cm 3/g; R ·1;,/(Per" Ve,) = 3.762 to 3.81 [39]. 1;" = 200°C, Pe, = 46.9 atm, and Oe, = 0.93 g/cm3 were caLcuLat ed in [28]. Vapor Pressure Orthorhombic MoF6. From 190 to 263.5 K, Ln p = 22.23 - 0.00956 T - 5735/T (p in atm, T in K) [12]. From -60to -8.7°C, Log p= 10.216-2166.5/T(p in Torr, T in K) [14]. From 194to 262.89± 0.14 K, Ln p = 24.0711- 5133.489/T (T in K, p ± 0.2 Torr) [10]. At 236.60 K, P = 10.62 Torr [40]; at 213 and 263.6 K, p=0.13 and 13 kPa, respectiveLy [41]. 262.89 ±0.14 K and 94.1 Torr are given for the orthorhombic-cubic tripLe point [10]. Cubic MoF6. From 263.5 to 290.76 K, Ln p=15.507(±0.001)-0.004134 T -4341/T (p in atm, Tin K) [12]. From -8.7 to +17.4°C, Log p=8.533-1722.9/T (p in Torr, Tin K) [14]. From 280 to 290 K, Log p=8.6492-1755.7/T (p±0.2%) [4]. To within ±0.2 Torr, between 262.89 (±0.14) and 290.95 (±0.11) K, Ln p=-17.43429-681.632/T+0.1385873 T-0.000171639 F [10]. At 266 K, p=14.7 kPa has been caLcuLated [45]. 290.95±0.11 K and 409.6 Torr [10] and 17.40°C and 398.1 Torr [14] have been given for the cubic-Liquid tripLe point. Liquid MoF6. Between 290.76 and 345 K, Ln p =14.455(± 0.0005) - 0.0055T -3919.8/T(p inatm) [12]. From 17.4 to 34°C, Log P = 7.766 -1499.9/T (p in Torr) [14]. In the approximate range from 44 to 88°C, Log P = (7.577 ± 0.005) - (1439.6 ± 1.9)/T [31,32], aLso see [42]. Between 35 and 90°C, Log p=7.545-1432/T [28]. The resuLt Log p=20.19354-2047.15/T-4.28004·Log T (p in Torr) determined between 291.15 and 320.15 K by [5] was incLuded in the approximate equation Log p = 8.02,29 -1865/T - 0.008421 T + 6.811 x1Q-6 T2 (p in bar) [4]. Between 290.95(±0.11) and 335 K, P (±0.4 Torr) is given by Ln p=25.24951-4357.644/T-0.0186598 T+0.000013847 T2 [10]. At 291.15 and 320.15 K, P = 412.85 and 1192.01 Torr, respectiveLy [5]. At 20°C, P = 350(?) Torr [17, 43]. At 50°C, p=2 atm [44], at 72.9°C, p=2600 [31] or 2612 Torr [32], at 85°C, p=5 atm [17]. References: [1] Heintz, A.; LichtenthaLer, R. N. (Ber. Bunsenges. Physik. Chem. 80 [1976] 962/5). [2] Morizot, P.; Ostorero, J.; PLurien, P. (J. Chim. Phys. Physicochim. Biol. 70 [1973]1582/6). [3] Morizot, P. (CEA-R-4380 [1973]1/113; C.A. 79 [1973] No. 83607). [4] MaLyshev, V. V. (TepLofiz. Vys. Temp. 12 [1974] 743/8; High Temp. [USSR] 12 [1974] 649/53). Gmelin Handbook Mo Su ppl. Vol. B 5 152 Molybdenum Fluorides [5] Osborne, D. W.; Schreiner, F.; Malm, J. G.; Selig, H.; Rochester, L. (J. Chem. Phys. 44 [1966] 2802/9). [6] Lichtenthaler, R. N.; Schramm, B.; Schäfer, K. (Ber. Bunsenges. Physik. Chem. 73 [1969] 36/41). [7] Brady, A. P.; Myers, O. E.; Clauss, J. K. (J. Phys. Chem. 64 [1960] 588/91). [8] Krause, R. F., Jr. (Proc. Electrochem. Soc. 78-1 [1978]199/209, 201). [9] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977]1149/63, 1152). [10] Meixner, D.; Heintz, A.; Lichtenthaler, R. N. (Ber. Bunsenges. Physik. Chem. 82 [1978] 220/5). [11] Brewer, L. (Proc. Electrochem. Soc. 78-1 [1978]177/86). [12] Brewer, L.; Lamoreaux, R. H. (At. Energy Rev. Spec. Issue No. 7 [1980] 11/191, 46/58). [13] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. (JANAF Thermochemical Tables, 3rd Ed., Pt. 11 [1985]1161/2). [14] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1563/8). [15] Hedge, W. D. (U.S. At. Energy Comm. K-1698 [1968]1/22, 7; C.A. 69 [1968] No. 70415). [16] Trevorrow, L. E.; Steindler, M. J.; Steidl, D. V. (Advan. Chem. Sero No. 71 [1967]308/19). [17] Rigny, P.; Virlet, J. (J. Chem. Phys. 47 [1967] 4645/52). [18] Braune, H.; Pinnow, P. (Z. Physik. Chem. B 35 [1937] 239/55, 244). [19] Ternisien, J. A. (Metaux 34 [1959] 151/61, 154). [20] Blinc, R.; Lahajnar, G.; Pirkmajer, E.; Zupancic, I. (Proc. Colloq. AMPERE 14 [1966/67] 1068171; C.A. 70 [1969] No. 15794). [21] O'Donnell, T. A. (J. Chem. Soc. 19564681/2). [22] Siegel, S.; Northrop, D. A. (Inorg. Chem. 5 [1966] 2187/8). [23] Nikolaev, N. S.; Opalovskii, A. A. (Zh. Neorgan. Khim. 4 [1959] 1174/83; Russ. J. Inorg. Chem. 4 [1959] 532/6). [24] Rakov, E. G.; Dzhalavyan, A. V.; Dudin, A. S. (Tr. Inst. Mosk. Khim. Tekhnol. Inst. No. 125 [1982] 82/7; C.A. 100 [1984] No. 166924). [25] Popov, A. P.; Tsvetnikov, A. K.; Goncharuk, V. K. (Zh. Neorgan. Khim. 23 [1978] 236/9; Russ. J. Inorg. Chem. 23 [1978]132/3). [26] Afanas'ev, M. L.; Gabuda, S. P.; Lundin, A. G.; Opalovskii, A. A.; Khaldoyanidi, K. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 4, pp. 18/22; C.A. 70 [1969] No. 52864). [27] Prusakov, V. N.; Korobtsev, V. P.; Markov, S. S.; Ezhov, V. K.; Khokhlov, V. A.; Bosenko, I. I. (Zh. Neorgan. Khim. 17 [1972] 2549/52; Russ. J. Inorg. Chem. 17 [1972]1334/6). [28] Nisel'son, L. A.; Nikolaev, R. K.; Sokolova, T. D.; Stolyarov, V. 1.; Korolev, YU. M. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 1, pp. 109/14; C.A. 69 [1968] No. 69834). [29] Bernhardt, H. A.; Bishop, H. W.; Brusie, J. P. (U.S. At. Energy Comm. TID-5212 [1955] 153/4; C.A. 1956 16499). [30] Prusakov, V. N.; Ezhov, V. K.; Lebedev, O. G.; Popov, V. K. (Ind. Chim. BeIge [2]32 [1967] Spec. No. Pt. 1, pp. 787/92, 789). [31] Carles, M. J.; Aubert, J. (J. Chim. Phys. Physicochim. Biol. 67 [1970] 671/5). [32] Reynes, J. A.; Carles, M. J.; Aubert, J. (J. Chim. Phys. Physicochim. Biol. 67 [1970]676/9). [33] Reynes, J.; Carles, M.; Aubert, J. (J. Chim. Phys. Physicochim. Biol. 67 [1970]1526/9). [34] Wagman, D. D.; Evans, W. H.; Parker, V. B.; Halow, 1.; Bailey, S. M.; Schumm, R. H. (NBS-TN-270-4 [1969]141 + XIII pp., 130). [35] Nuttall, R. L.; Kilday, M. V.; Churney, K. L. (AD-782028 [1973] 110+XIII pp., 78/89). [36] Dittmer, G.; Niemann, U. (Mater. Res. Bull. 18 [1983] 355/69). Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 153 [37] Galkin, N. P.; Bertina, L. E.; Orekhov, V. T.; Paklenkov, E. A. (Zh. Fiz. Khim. 49 [1975]2454; Russ. J. Phys. Chem. 49 [1975] 1443). [38] Malyshev, V. V. (Teplofiz. Svoistva Gazov 1976 97/105; Ref. Zh. Khim. 1977 No. 2B771). [39] Verkhivker, G. P.; Tetel' baum, S. D. (Termodin. Termokhim. Konstanty 197028/32; C.A. 74 [1971] No. 15771). [40] Douglas, T. B.; Krause, R. F., Jr. (AD-782028 [1973] 110 + XIII pp., 90/110). [41] Levy, J. H.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975] 398/401). [42] Carles, M. J.; Reynes, J. A.; Bethuel, L.; Aubert, J. (CEA-CONF-2171 [1972]1/8; C.A. 79 [1973] No. 140116). [43] Ursu, 1.; Bogdan, M.; Fitori, P.; Darabont, A.; Demco, D. E. (Mol. Phys. 56 [1985]297/302, 298). [44] Claassen, H. H.; Selig, H.; Malm, J. G. (J. Chem. Phys. 36 [1962] 2888/90). [45] Levy, J. H.; Sanger, P. L.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975]1065/7). 2.2.8.4.3 Thermodynamic Data Heat Capacity The heat capacity Csat of MoF6 under its saturated vapor was measured between 3.55 and 347.52 K (0.018 and 42.619 cal' mol-1 • K-l), see Fig. 46, p. 154; see also the tables for Csat and C~ (under constant pressure of 1 atm) given in the paper [1]. Following are the older Csat values from [2]: Csat in cal' mol-1 • K-1 ...... 11.81 13.77 16.50 17.10 T in K ...... (orthorhombic) 50 60 70 80 Csat in cal· mol-1 • K-l ...... 18.67 20.12 22.52 25.14 27.30 29.43 Tin K ...... 90 100 120 140 160 180 Csat in cal·mol-1 ·K-1 ...... 31.48 33.65 35.97 Tin K ...... 200 220 240 Csat in cal· mol-1 • K-1 ...... 36.17 36.68 39.61 T in K ...... (cubic) 273.15 280 (liquid) 298.15 The C~ values for liquid MoF6 between 200 and 1000(?) Kare listed in [3]. For values up to 400K, see [4, 5]. Between 291 and 400 K, C~R=14.180+0.020934 T (±0.03) [5]. For the melting point, 290.76 K, C~ = 37.820 and 40.275 cal· mol-1 • K-l have been given for solid and liquid MoF6 in the reviews [4, 5]. For the liquid at 298.15 K under 1 atm, C~ = 40.582 [1] (also given in [4,5]),40.58 cal·mol-1.K-l [6],169.795 J·mol-1 ·K-1 (,~40.581cal·mol-l·K-l) [3]. Gaseous MoF6 (values calculated from spectroscopic data). C~ values are calculated for T = 50 to 1000 K [1], for 200 to 2000 K [7], 250 to 400 K (50 K steps) and 400 to 1000 K (100 K steps) [8]; for T=100to 1500 K, also see [9]. For 298 to 3000 K, C~R =18.50 + 1.928 x10-4 T - 370 150r2 (± 0.07) [5]. For T = 500 to 3000 K, C~ increases from 33.601 to 37.620 cal· mol-1 • K-l according tothe reviews [4, 5]. The C~ valuesforthe ideal MoF6 gas between Oand 6000 Kare listed in [3]. Gmelin Handbook Mo Suppt. Vot. B 5 154 Molybdenum Fluorides Fig. 46. Heat capacity CSal of MoFe under its saturated vapor vs. temperature [1]. Temperature in K C~ = 27.544 [8] and 27.22 cal· mol-1. K-1 [9] at 273.15 [8] and 273.16 K [9], respectively. For 298.15 K, C~=28.747 [4,5], 28.816 [1] (28.82 [6]), 28.610 cal·mol-1·K-1 [8],120.276 J·mol-1 . K-1 (~28.746 cal· mOl-1. K-1) [3]. For 298.16 K, the values 29.7651 [7] and 28.35 cal· mol-1. K-1 [9] are given. Entropy and Other Data Solid MoFe. In orthorhombic MoFe, ST ranges from 0.024 at 5 K to 46.464 cal· mol-1. K-1 at 263.50 K.ln cubic MoFe, ST ranges from 53.876 at 263.50 K to 57.490 cal· mol-1. K-1 at 290.76 K [1]. Liquid MoFe. The calorimetric value S~8.15 of 62.061 ±0.06 cal· mol-1. K-1 [1] is in excellent agreement with the value 61.96 recalculated by [1] from the calorimetric data of [2] who erroneously gave the value 60.6 [2]. S~8.15 = 62.06 is given in [6]. S298.15 = 62.061 ± 0.06 cal· mol-1. K-1 (S~alR = 31.231 ±0.03 [4]) is recommended in the reviews [4,5]; S29815= 259.693 ±0.25 J·mol-1·K-1 (~62.067 cal·mol-1·K-1) [3]. ST ranges from 61.047 at 290.76 K to 68.736 cal·mol-1·K-1 at 350 K [1]; values from 200 to 1000 Kare listed in [3]. Gaseous MoFe. The calorimetric S~815 value of 83.75 ±0.10 cal· mol-1. K-1 [1] is in excellent agreement with the spectroscopic value 83.77 [10] (83.765 [1]) calculated using the rigid rotor harmonic oscillator approximation for the frequency assignment given in [10] and an Mo-F distance of 1.840 A [1]. The value 83.75 is given in [6]. The calorimetric value 80.6 ± 0.7 [2] (wh ich revises the 79.7 ± 0.6 given in [11]) is low because of the ~Svap = 20.1 cal· mol-1. K-1 value of [2] which is lower than the more accurate 22.237 ± 0.08 of [1]. Spectroscopic values given are S298 = 84.295 [12], S~8.15=81.303 [8], and 83.8688 cal·mol-1·K-1 [7]. S29815=83.795 ±0.03 cal· mol-1. K-1 (S~alR = 42.168 ± 0.01 [4]) is recommended in the reviews [4, 5]; S~8.15= 350.710±0.42 J·mol-1·K-1 (~83.820 cal·mol-1·K-1) [3]. For gaseous MoFe, ST increases from 100.017 to 165.473 cal· mol-1. K-1 as T increases from 500 to 3000 K [4, 5]; 93.213 to 191.775 for Tranging from 400 to 6000 K [12]; 73.3486 to 150.5424 for T = 200 to 2000 K [7]; from 50.420 at 50 K to 124.541 at 1000 K [1]. For T = 250 to 400 K, also see [8]. Values between 0 and 6000 Kare listed in [3]. Values for _{Go - H~8)/T and H" - H~8 are listed between 200 and 1000 K for liquid MoFe and between 0 and 6000 K for gaseous MoFe [3]. For acheck of the thermodynamical similarity of SFe, MoFe, WFe, and UFe liquids and vapors, see [13]. Gmelin Handbook Mo Suppl. Vol. B 5 MoFa 155 Thermodynamic Data of Formation ßH,. Liquid MoFa. By solution calorimetry, ßHi,298 = -1591.30 ± 3.72 kJ/mol {a -380.33 ± 0.89 kcaUmol} [14). Using a heat of vaporization of 6.6 kcaUmol and the {recalculated} ßH, value of gaseous MoFa from [15]. ßHj.298 = -1585.53 ±0.92 kJ/mol {a -378.95 ± 0.22 kcaUmol} has been calculated [14). The more negative value ßHi,2981S = -388.6 ± 4 kcaUmol [16) is obso lete, -378.95 kcaUmol is given in [6), and -379.189 ± 1.883 kcaUmol is recommended in [17); ßHj.298.1S= -1585.656 ±0.11 kJ/mol {a -378.97 kcaUmol} [3). The value ßHj.mlR = -190720 ± 120 K results when small corrections are applied in response to changes in the accepted values of the atomic weights [4, 5). ßHj.o = -381.733 kcaUmol [6). ßH, values for temperatures between 200 and 1000 Kare listed in [3). Gaseous MoFa. By solution calorimetry {MoFa in 1M and 0.1M aqueous NaOH}, ilHj.298.2= -1564 kJ/mol {a-373.8 kcaUmol} [19). By fluorine bomb calorimetry {in an Ni bomb}, ilHj.298.1S= -372.35±0.22 kcaUmol [15) (also see [20)). Due to changes in the accepted values of the atomic weights, the value given in [15) has to be changed to ilHj.2981S = -372.31 ± 0.22 kcaUmol [21). Based on the result of [15) and data from [1), the value ßHi,298.1S = -372.506 ± 1.868 kcaUmol is recommended in [17), ßHi,298.1S= -372.29 kcaUmol is given in [6); see also the -1558 kJ/mol {a-372 kcaUmol} in [16). ßHi,298.1S=-1557.661±0.92 kJ/mol {a -372.28 kcaUmol} [3). The value ilHj.29a1R = -187355 ± 110 K results when small corrections {see above} were applied [4, 5). ßHi,o = -370.27 ± 0.23 [1]. -370.608 kcaUmol [6), and -1550.595 ± 0.92 kJ/mol {a -370.59 kcaUmol} [3); see also [18). ilH, values between 0 and 6000 K are listed in [3). ßG,. For liquid MoFa, ßGj.298.1S = -352.08 kcaUmol [6), -1473.170 kJ/mol {a -352.088 kcaUmol} [3). ilGi,mlRT= -594.3±0.4 [4). ilGj values for 200 to 1000 Kare listed in [3). For gaseous MoFa, ilGj.298.1S = -351.88 [6), -351.91± 0.23 [1), -350.8 ± 0.22 kcaUmol [15), and -1472.312 kJ/mol {a -351.882 kcaUmol} [3). ßGi,29a1RT = -594.0 ± 0.3 [4). ßGj values for temperatures between 0 and 6000 Kare listed in [3). log Kf • For liquid MoFa, log Kf values between 200 and 1000 K and for gaseous MoFa between 0 and 6000 Kare listed in [3). References: [1) Osborne, D. W.; Schreiner, F.; Malm, J. G.; Selig, H.; Rochester, L. (J. Chem. Phys. 44 [1966) 2802/9}. [2) Brady, A. P.; Myers, O. E.; Clauss, J. K. (J. Phys. Chem. 64 [1960) 588/91}. [3) Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. {JANAF Thermochemical Tables, 3rd Ed., Pt. 11 [1985) 1161/2}. [4) Brewer, L. (Proc. Electrochem. Soc. 78-1 [1978) 177/86}. [5) Brewer, L.; Lamoreaux, R. H. {At. Energy Rev. Spec. Issue No. 7 [1980)11/191, 46/58}. [6) Wagrrran, D. D.; Evans, W. H.; Parker, V. B.; Halow, 1.; Bailey, S. M.; Schumm, R. H. {NBS- TN-270-4 [1969) 141 + XIII pp., 130}. [7) Nagarajan, G.; Brinkley, D. C. {Z. Naturforsch. 26a [1971) 1658/66}. [8) Claassen, H. H.; Selig, H.; Malm, J. G. (J. Chem. Phys. 36 [1962) 2888/90}. [9) Sundaram, S. (Z. Physik. Chem. [Frankfurt) 34 [1962) 225/32}. [10) Weinstock, B.; Goodman, G. L. (Advan. Chem. Phys. 9 [1965) 169/319, 197/9}. [11) Brady, A. P.; Clauss, J. K.; Myers, O. E. (WADC-TR-56-4 [1955)1/55 from N.S.A. 10 [1956) No. 898}. [12) Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. {Termodinamicheskie Svoistva Neorgani cheskikh Ftoridov, Atomizdat, Moscow 1972, pp. 1/144}. [13) Malyshev, V. V. {Teplofiz. Vys. Temp. 14 [1976)47/55; High Temp. [USSR)14 [1976) 41/7}. Gmelin Handbook Mo Suppl. Vol. B 5 156 MOlybdenum Fluorides [14] Nuttall, R. L.; Kilday, M. V.; Churney, K. L. (AD-782028 [1973]110 + XIII pp., 78/89); Nuttall, R. L.; Churney, K. L.; Kilday, M. V. (J. Res. Natl. Bur. Std. 83 [1978] 335/45). [15] Settle, J. L.; Feder, H. M.; Hubbard, W. N. (J. Phys. Chem. 65 [1961]1337/40). [16] Rakov, E. G.; Dzhalavyan, A. V.; Dudin, A S. (Tr. Inst. Mosk. Khim. Tekhnol. Inst. No. 125 [1982] 82/7; C.A. 100 [1984] No. 166924). [17] Barnes, D. S.; Pedley, J. B.; Kirk, A; Winser, E.; Heath, L. G. (Comput. Anal. Thermoehern. Data 1974 1/30,11). [18] Dellien, 1.; Hall, F. M.; Hepler, L. G. (Chem. Rev. 76 [1976] 283/310, 299). [19] Burgess, J.; Haigh, 1.; Peaeoek, R. D. (J. Chem. Soe. Dalton Trans. 1974 1062/4). [20] Settle, J. (ANL-6231 [1960]1/182,83/5; N.S.A. 15 [1961] No. 12649). [21] O'Hare, P. A. G.; Benn, E.; Cheng, F. Y.; Kuzmyez, G. (J. Chem. Thermodyn. 2 [1970]797/804, 800). 2.2.8.5 Electrical and Magnetic Properties The molar pOlarizability Pmol = 5.52 em3/mol (dieleetrie eonstant E =1.22) is given for obvi ously liquid MoFs (temperature not stated) [1]. For the gas, between 39.8 and 144.7°C, Pmol is seattered between the mueh larger values 29.31 and 30.16 em 3/mol [2]. The magnetie suseeptibility Xwas measured by the Gouy method as Xg = -0.124 x 10- 6 em 3/g or Xm = -26 x10-6 em 3/mol ([3] obviously eiting [4]). A van Vleek-type eontribution Xvv = +44 x 10- 6 em3/mol was assumed in view of the diamagnetism of Mos+ and F- ions (XvV = +27 x 10-s em3/mol was also eonsidered in the paper) [3]. XvV = +29 X lO-s em3/mol aeeording to [5]. References: [1] Isakov, V. P. (lh. Fiz. Khim. 47 [1973] 702/4; Russ. J. Phys. Chem. 47 [1973] 395/6). [2] Morizot, P. (CEA-R-4380 [1973]1/113; C.A. 79 [1973] No. 83607). [3] Tilk, W.; Klemm, W. (l. Anorg. Allgern. Chem. 240 [1939] 355/68, 362). [4] Henkel, P.; Klemm, W. (l. Anorg. Allgern. Chem. 222 [1935] 70/2). [5] Rigny, P.; Virlet, J. (J. Chem. Phys. 47 [1967] 4645/52). 2.2.8.6 Optical Ptoperties 2.2.8.6.1 Color MoFs is deseribed as a eolorless [1, 5] or nearly water-elear liquid [2], and as a elear, eolorless liquid [3]. At -80°C, MoFs forms a white solid whieh melts at room temperature to a eolorless liquid [4]. References: [1] Braune, H.; Pinnow, P. (l. Physik. Chem. B 35 [1937] 239/55, 244). [~] Burke, T. G.; Smith, D. F.; Nielsen, A. H. (J. Chem. Phys. 20 [1952] 447/54). [3] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chern. Soc. 73 [1951]1164/7). [4] Gaunt, J. (Trans. Faraday Soe. 49 [1953] 1122/31). [5] Rakov, E. G.; Dzhalavyan, A. V.; Dudin, A. S. (Tr. Inst. Mosk. Khim.-Tekhnol. Inst. No. 125 [1982] 82/7; C.A 100 [1984] No. 166924). Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 157 2.2.8.6.2 Raman Spectrum Solid. Orthorhombic single erystals (faetor group D2h) at 77 K showed altogether forty-four Stokes shifts, ranging from 1482.79 to 30.9 em-I and eomprising internat and external modes. Due to the site symmetry Cs all moleeular vibrations are Raman-aetive. For the fundamentals and the phonons the theoretieal and observed numbers (N) of modes together with their ob served wavenumbers (v) or ranges of v are given in the following table grouped aeeording to their parent moleeular vibrations [10]: parent mode .... VI V2 V3 V4 Ntheor ...... 2 4 6 6 Nobs ...... 4 4a) 6 v in em-I ...... 742.19 652.45 to 642.43 721.64 to 694.60 275.81 to 247.62 parent mode ".' . Vs Vs rotation and translationb) Ntheor ...... 6 6 12 Nobs ...... 3 1 8 v in em-I ...... 324.78, 319.50, 140 128 to 30.9 316.02 a) Higher-energy eomponents probably buried under VI. - b) "External" modes yielding erystal phonons. For higher harmonies (2vI at 1482.79 to 2V6 at 278.20 em-I) and eombination bands, see the paper [10]. Properties of exeiton states were diseussed in [11] and studied also on solid solutions with other hexafluorides in [12]. VI (at 743.5) and split V2 (653, 641) and v5 (325, 320, 315 em-I) were observed earlier [6]. For the cubic modifieation, shifts at 742.5, 647, and 323 em-I were observed [6]. The linewidths at O°C agreed with those of the liquid [7]. Liquid. Laser exeitation at room temperature led to VI =743.5, v2=647, and v5=326 em-I [6]. For shifts against the gas-phase speetrum (as published in [5]) and for linewidths, see [7]. Older results are 741,645, and 322 em-I [8] and (relative peak intensities 1 and depolarization ratios Q in parentheses) 736 (I=10, Q=0.09), 641 (3, 0.94), and 319 em-I (3, 0.98) [9]. Vapor. For an isotopicallyenriched 1CXJ MoF6 sampie (>97%), the following wavenumbers v, relative peak intensities I, and depolarization ratios Q were measured with the saturated vapor at 300 K. The stronger bands, VI, V2' V5' and 2V6' were studied for 92MoF6, too, and showed no signifieant isotopie shifts. The shifts of 2V4 and V4+V6 have not been determined [1]: v{'OOMoF6) in em-I .... 741.8 ±0.3 652.0±0.5 531±3 380±3 317±1 233±2 1 ...... 100 6. 0.07 0.15 4.5 0.6 Q ...... 0.01 0.74 0.77 0.5 assignment ...... VI V2 2V4 V4 + V6 Vs 2V6 The VI band eonsisted of a Q braneh with an estimated ÖVy, of 1.5 em-I. The V2 band showed rotational branehes (OP, Q, RS) with aseparation of ÖVOP,RS =16.2 ±0.5 em-I. No strueture was resolved with the remaining bands; estimated half widths are öVy, = 23 (vs) and 38 em-I (2V6) [1]. For natural MoF6 the bands VI = 741.5 ± 0.3 (highly polarized), V2 = 651.6 (Q near 0.75), 2V4 = 534, V4 +V6 = 389, v5=318 (Q near 0.75), and 2V6= 233 em-I were observed at 70°C and 2 atm [2], and VI = 741.6, V2 = 650.9 (ÖVOP,RS =18.2 em-I), v5 = 318.4 em-1 (all ± 0.5 em-I), and 2v6 = Gmelin Handbook Mo Suppl. VOt. B 5 158 MoLybdenum Fluorides 229±2 cm-1 at 378 K [3]. V1 =742±0.8 cm-1 at room temperature and 100 Torr [4]; V1 =741 ±1 and v2=643±5 cm-1 with the saturated vapor at 50°C [5]. Solutions. Saturated soLution in HF at room temperature: V1 = 744 ± 0.5, V2 = 651 ± 2, Vs = 320±2 cm-1 [13]. In CH3CN: V1 =740 cm-1 [14]. References: [1] McDoweLL, R. S.; Sherman, R. J.; Asprey, L. B.; Kennedy, R. C. (J. Chem. Phys. 62 [1975] 3974/8). [2] CLaassen, H. H.; Goodman, G. L.; HoLLoway, J. H.; Selig, H. (J. Chem. Phys. 53 [1970]341/8). [3] Bosworth, Y. M.; CLark, R. J. H.; Rippon, D. M. (J. Mol. Spectrosc. 46 [1973]240/55, 242). [4] Cahen, J.; CLerc, M.; Isnard, P.; Rigny, P.; WeuLersse, J. M. (Nonlinear Behav. Mol. At. Ions ELectr. Magn. ELectromagn. FieLds Proc. 31st Intern. Meeting Soc. Chim. Phys., Abbaye de Fontevraud, Fr., 1978 [1979], pp. 127/39, 132; C.A. 91 [1979] No. 65652). [5] CLaassen, H. H.; SeLig, H.; MaLm, J. G. (J. Chem. Phys. 36 [1962] 2888/90). [6] GiLbert, M.; Drifford, M. (Advan. Raman Spectrosc. 1 [1972] 204/14, 20617). [7] GiLbert, M.; Drifford, M. (Mol. Motions Liq. Proc. 24th Ann. Meeting Soc. Chim. Phys., Paris-Orsay, Fr., 1972 [1974], pp. 279/86; C.A. 82 [1975] No. 162303). [8] Burke, T. G.; Smith, D. F.; NieLsen, A. H. (J. Chem. Phys. 20 [1952] 447/54). [9] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951]1164/7). [10] Bernstein, E. R.; Meredith, G. R. (Chem. Phys. 24 [1977] 289/99, 291). [11] Bernstein, E. R.; Meredith, G. R. (Chem. Phys. 24 [1977]301/9). [12] Bernstein, E. R.; Meredith, G. R. (Chem. Phys. 24 [1977] 311/25). [13] FrLec, B.; Hyman, H. H. (Inorg. Chem. 6 [1967]1596/8). [14] Prescott, A.; Sharp, D. W. A.; WinfieLd, J. M. (Chem. Commun. 1973 667/8). 2.2.8.6.3 IR Spectrum Solid. The foLLowing absorption maxima (positions in cm-1) were observed at -180°C. The assignments (in parentheses) were based on the site group Cs: 318 and 326 (vs), 463 and 477 (erroneousLy 2vs), 510 and 520 (2V4)' 645 (V2), -740 (V3 and V1), 900 (V2 + v4),970 (V2 + vs), 1030 (v3+vs),1250(V3+2v4),1355(V2+V3),1423(-),1453(2v30rv1+V30r2v1),and 1515(-) [12]. Vapor. High-resoLution spectra in the region of the V3 fundamentaL (740 to 750 cm-1) were obtained with a tunabLe Laser for isotopicaLLy enriched [1] and for naturaL sampLes [1 to 3]. The Q-branch absorption spectra of 92MoFs, 96MoFs, and 1ooMoFs (aLL 97% purity), each covering a range of -0.2 cm-1, were measured at 195 K. Five (92MoFs) or four "subband heads" were observed. Their positions yieLded the (isotopic) band centers (see p. 133) and the effective perturbations to the rotationaL constants (see p. 131). ALso, the octahedraL spLitting constants g=-1.5, -1.0, and -2.0x1Q-s cm-1 were obtained for the 92Mo, 9sMo, and 1ooMo species, respectiveLy [1]. Spectra at Lower temperatures were obtained bya supersonic jet using a puLsed nozzLe. At -80 K, the 1ooMoFs Q-branch subband heads (around 741.3 cm-1) were observed with an isotopicaLLy pure as weLL as with a naturaL sampLe [1]. Q branches of 9sMoFs and of 96MoFs, both measured with a naturaL sampLe, are shown in [2]. IndividuaL P- and R-branch Lines, showing octahedraL fine-structure splitting for the higher J vaLues, were identified in [3] and yieLded severaL vibrationaL and rotationaL constants (see pp. 131, 133). Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 159 Lower-resolution spectra over the range -1500 to -250 cm-1 were obtained for two isoto pically enriched sampies (>97.4%) at 300 K. The wavenumbers (in cm-1) given below indicate the points of maximum absorbance in the Q branch and are accurate to ± 0.5 cm-1 [4): sampie 1487.3 1394.6 916.1 747.2 265.7 1479.4 1386.4 913.1 739.3 262.7 At 300 K. the fundamental V3 showed a partially resolved PQR structure. which sharpened at 200 K. The P-R separations of V3 and v4 were derived from the calculated Coriolis constants (see p. 135) as 11.6 cm-1 forv3 and 10.8 cm-1 forv4 at 300 K. consistent with the observed band contours [4). The absorption bands in conventional spectra of natural MoFs are broad and featureless due to severe overlapping of isotopic and hot bands [4). The assignments made in [5 to 7) were critically reviewed and partly changed in [8). The following table shows observed wave numbers v and intensities I of the fundamentals and the more prominent (binary) combination bands. For additional features. see the remarks and the text below: v in cm-1 ...... 264 [4. 5) 435 [5. 7) 480 [5) 741 [4.5.7) 763 [6. 10) I from [7) ...... m vw vs m assignment by [8) ... V4 vs+vs V1- V4 V3 V2+ VS remark ...... a) b) c) d) V in cm-1 ...... 915 [4) 1005 [5) 1052 [4. 6. 7) 1390 [4.5) 1482 [4) I from [7) ...... w vw w m m assignment by [8) ... V2+ V4 V1 +v4 V3+ VS V2+ V3 V1+V3 remark ...... e) f) g) h) a) 260 cm-1 [7). - b) 434 cm-1 [6). - c) 740.7 [10). 741.1± 0.3 [9). 742 cm-1 [6). - d) 764 cm-1 [7). e) 914 [5.6).913 cm-1 [7.10). - f) 1004 [6). 1002 cm-1 [7). -g) 1054 cm-1 [5). Used for multiple photon isotope separation by CO2-laser radiation [2. 11). - h) 1389 [10). 1385 [7). 1384 cm-1 [6). - i) 1479 [5). 1480 [7). 1481 cm-1 [6.10). Additional features (in cm-1): v= 453 [5). 455{vw) [7).456 [6). v = 648{w) [7). v = 777{m) [7). 776 [10). assigned to 3V4 [7). v = 832 [5).833 [6. 7). v = 882 [6. 7) (vw [7)). ascribed to an impurity by [5). v=970{vw) [7). 983 [6. 7). v=1156 (assigned to a ternary combination band) [6). 1175{vw) [7). v=1265{vw) [7). 1262 [6). Five very weak [7) ternary combination bands were observed at (v from [6). followed by v from [7) in parentheses) 1590 (1585). 1743 (1740). 2032 (2030). 2128 (2125). and 2218 (2215) cm-1. Solid solutions obtained by freezing a liquid Xe solution of natural MoFs were studied at 81 K. The isotopic splitting of the V3 absorption band was fully resolved: V3 = 735.31 cm-1 for 92MoFs• 727.09 cm-1 for 1ooMoFs [13). In an Ar matrix (MoFs :Ar =1: 500) at 6 ± 1 K the isotopic structure of V3 was partly resolved (743.5 to 733.5 cm-1). Absorption due to V4 (at 261.0 cm-1). and several polymer peaks (443. 517. 706. 724. and 783 cm-1) were also found [14). An Ar matrix at 20 K was previously used [15). GmeLin Handbook Mo Suppl. Vol. B 5 160 MoLybdenum Fluorides References: [1] Cummings, J. C. (J. Mol. Spectrosc. 83 [1980] 417/30). [2] Oyama, T.; Watanabe, T.; Tashiro, H.; Takami, M. (Reza Kagaku Kenkyu 5 [1983]109/13; C.A. 100 [1984] No. 75882). [3] Takami, M.; Matsumoto, Y. (Mol. Phys. 64 [1988]645/58, 646/9); Matsumoto, Y.; Takami, M. (Reza Kagaku Kenkyu 8 [1986] 13/5; C.A. 106 [1987] No. 164845). [4] McDoweLL, R. S.; Sherman, R. J.; Asprey, L. B.; Kennedy, R. C. (J. Chem. Phys. 62 [1975] 3974/8). [5] CLaassen, H. H.; Selig, H.; MaLm, J. G. (J. Chem. Phys. 36 [1962] 2888/90). [6] Gaunt, J. (Trans. Faraday Soc. 49 [1953] 1122/31, 1127). [7] Burke, T. G.; Smith, D. F.; NieLsen, A. H. (J. Chem. Phys. 20 [1952] 447/54). [8] Weinstock, B.; Goodman, G. L. (Advan. Chem. Phys. 9 [1965]169/319, 199). [9] CLaassen, H. H.; Goodman, G. L.; HoLLoway, J. H.; SeLig, H. (J. Chem. Phys. 53 [1970]341/8). [10] Rak, V.; Sara, V.; ULLrich, J.; VeseLy, V. (Ustav Jad. Vyzk. 3282-Ch [1974]1/13; C.A. 85 [1976] No. 28197). [11] Freund, S. M.; Lyman, J. L. (Chem. Phys. Letters 55 [1978] 435/8). [12] HeLLberg, K. H.; MüLLer, A.; GLemser, O. (Z. Naturforsch. 21 b [1966] 118/21). [13] HoLLand, R.; Maier, W. B., 11; Freund, S. M.; Beattie, W. H. (J. Chem. Phys. 78 [1983] 6405/14, 6405, 6413). [14] BLinova, O. V.; Predtechenskii, Yu. B. (Opt. Spektroskopiya 47 [1979] 1120/5; Opt. Spectrosc. [USSR] 47 [1979] 622/4). [15] Acquista, N.; Abramowitz, S. (J. Chem. Phys. 58 [1973] 5484/8). 2.2.8.6.4 UV spectrum The eLectronic absorption spectrum of the saturated vapor was measured between 250 and 110 nm at pressures p = 0.15 to ?;4 Torr. The vibronic progressions observed in four absorp tion systems were ascribed to the totaLLy symmetric Mo-F stretching vibration in the respective eLectronicaLLy excited states. In the foLLowing tabLe vmax gives the wavenumbers of maximum absorption and of the most prominent peak of the progressions for structureLess and struc tured systems, respectiveLy [1] ("verticaL excitation"; see [2, 3]). The extinction coefficients f max [1] are apparentLy given in L·moL-l· cm-l (see, e.g. [4]). For the structured systems, the number N of observed peaks and their average separation I'!v are aLso given [1]. In the papers [2, 3, 5] the originaL assignments to one-eLectron transitions [1] were Later partLy changed (see beLow). The orbitaL numbering was made consistent with the eLectron configuration given on p.122. vmax incm-1 from[1] ..... 47600 52763 57500 69546 f max from [1] ...... 500 2200 5000 50 Nfrom [1] ...... 14 8 I'!v in cm-1 from [1] ...... 630 609 b) a) c).d) remark ...... a) Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 161 Vrnax in cm-1from [1] .... . 74377 81014 ~87700 Ernax from [1] ...... <20 600 ~3000 N from [1] ...... 5 14 ~vincm-1from[1] ...... 562(?) 600 assignment ...... 3 t29 <- 2 t2g [2] 3t2g <-4eg [2] 5eg<-7t1u [1] a),e) remark ...... d) a) StructureLess absorption system, - b) The center of this system was estimated previousLy to be at ~185 nm [6] (cited as v=54000 cm-1 in [7]); ~v=639 cm-1 [6], see aLso beLow. - c) v rnax =69541 cm-1 in a tabLe of aLL peaks [1]. - d) Beginning of the progression uncertain. e) An assignment 5eg <-1t1g was aLso considered [1]. At 532 Torr a continuous absorption extended to shorter waveLengths from ~281.5 nm (v = 35524 cm-1). Diffuse bands were observed at much reduced pressures (0.35 to 0.15 Torr). Increasing absorption coefficients a (a·1o = Ln 1/10 with 10 in cm at ODC and 760 Torr) were measured between 281.5 nm (a = 0.09) and 197 nm (a =176) [6]. The onset frequency for the intramoLecuLar charge-transfer transitions at 77 K is given as 50000 cm-1 in a study on solid soLutions of 0.5% MoF6 in Xe while the onset of the intermoLecuLar charge transfer is at 26300 cm-1 [8]. The two strong transitions at V rnax = 52763 and 57500 cm-1 are ascribed to three opticaLLy aLLowed (g_u) excitations (the transitions from 7t1u and 1t2u are assumed to be opticaLLy unresoLved), The other transitions with V rnax from 47600 to 81 014 cm-1 are considered as g_g transitions [2] (foLLowing the leveL ordering caLcuLated for MoF6 [3] and for WF6 [11]). The v=47600 cm-1 transition was assigned to t29 <-t1g and the v~87700 cm-1 transition was assigned to eg<-(t1g or t 1u) [1]. The assignments given in [1] were based on a qualitative moLecuLar orbitaL LeveL diagram from [9], on intensity ruLes from [7], and on a comparison with the WF6 spectrum aLso measured in [1]. The assignments for the transitions with 52763 cm-1~ v~81 014 cm-1 given in [1] have been revised in [2] mainty on grounds of the photoeLectron spectrum (PES) of MoF6 meanwhiLe measured by [10] and the Xa-scattered wave caLcuLations [3,5] interpreting the PES given in [10]. TheoreticaL transition energies were obtained from an Xa-SW caLcuLation with atomic spheres overLapping by 20% (making the first ionization energy agree with the vaLue measured in [10]). The transition-state method then yieLded v (in 104 cm-1): 5.32, 5.54 and 5.73, 5.95, 6.6, and 6.96 for the first five transitions (see the tabLe above) [5]. Energies E were caLcuLated from E = Ei - A - Q, using ionization energies Ei measured by [10], eLectron affinities A from an Xa-SW caLcuLation with overLapping spheres, and Q adjusted to 4.40 eV (making caLcuLated and experimentaL energies of the first transition agree). The resuLting energies (in 104 cm-1) are 4,74, 5.32, 5.9, 6.79, 7.53, and 7.97 for the first six transitions, and ~ 8881 0 cm-1 for 5eg <-1t1g and ,~94690 for 5eg<-7t1u 13]. Transition energies were aLso caLcuLated by severaL modified versions of the Xa-SW method [12]. An Xa-discrete variational caLcuLation yieLded vaLues for the orbitaL energy differences [13]. References: [1] McDiarmid, R. (J, Chem. Phys. 61 [1974] 3333/9). [2] McDiarmid, R. (Chem. Phys. Letters 76 [1980] 300/3). [3] BLoor, J. E.; Sherrod, R. E. (J. Am. Chem, Soc. 102 [1980] 4333/40). [4] McDiarmid, R. (J. Mol. Spectrosc. 39 [1971] 332/9), [5] TopoL', I. A.; Dement'ev, A. 1.; Rambidi, N. G,; Nefedov, V. I. (Koord, Khim. 5 [1979]860/5; Soviet J. Coord. Chem. 5 [1979] 676/80). GrneLin Handbook Mo Suppl. Vol. B 5 11 162 Molybdenum Fluorides [6] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951]1164/7). [7] Jf2Irgensen, C. K. (Absorption Spectra and Chemical Bonding in Complexes, Pergamon, New York 1962, pp. 157,287). [8] Webb, J. D.; Bernstein, E. R. (J. Am. Chem. Soc. 100 [1978] 483/5). [9] Henning, G. N.; Dobosh, P. A.; McCaffery, A. J.; Schatz, P. N. (J. Am. Chem. Soc. 92 [1970] 5377/82). [10] Karisson, L.; Mattsson, L.; Jadrny, R.; Bergmark, T.; Siegbahn, K. (Phys. Scr. 14 [1976] 230/41, 235/9). [11] Ellis, D. E.; Rosen, A. (Z. Physik A 283 [1977] 3/10). [12] Onopko, D. E. (Khim. Fiz. 5 [1986]1572/4; C.A. 106 [1987] No. 75093). [13] Gutsev, G. L.; Levin, A. A. (Chem. Phys. 51 [1980]459/71,466). 2.2.8.7 Electrochemical Behavior The electrochemical behavior of MoF6 was studied in neutral (0.5 M KBF4) and basic (NaF) anhydrous HF solutions at Pt and glassy carbon electrodes by cyclic voltammetry. On Pt, two successive chemically reversible one-electron reduction reactions having half-wave potentials EV2 =0.91 and 0.31 V, respectively, occur. They can be described by MoF6 +e-;;:=MoF6" and MoF6" +e-;;:=MoF~-. On glassy carbon electrodes, the waves are quasi-reversible. Under ac conditions two well-defined symmetrical waves are obtained implying fast electron transfer for both steps. A comparison with WF6, which also exhibits reversible electrochemical behavior, shows that the reduction potential for the MoF6/MoF6" couple is about 1 V more positive than that for WFJWF6". On addition of H20 to a solution of MoF6 in either neutral or basic anhydrous HF solution the reduction waves of MoF6 disappear at mole ratios H20: MoF6 =1: 1 up to 2: 1 and a new reduction wave appears corresponding to that of MoOF4 in the same medium. Bond, A. M.; Irvine, I. 1.; O'Donnell, T. A. (Inorg. Chem. 16 [1977] 841/4). 2.2.8.8 Chemical Reactions Survey. MoF6 (like WF6) exhibits an extreme sensitivity to moisture and requires special precautions for handling. This striking behavior probably contributed to the assumption in the earlier literature that MoF6 is highly reactive and almost identical with WF6 in its chemical properties. However, examination of the reactions with numerous compounds showed that MoF6 is only a mild f1uorinating agent and is relatively inert as an oxidant. The reactivity with respect to f1uorination decreases in the order CrFs>UF6>MoF6>WF6, and with respect to oxidizing strength in the order VFs>UF6>MoF6>WF6>NbFs=TaFs. Either reduction of the hexafluoride to lower fluorides or mere halogen exchange occurs more readily with the molybdenum than with the tungsten compound. MoF6 behaves like UF6 rather than WF6 which is surprisingly inert [1 to 3]. References: [1] Canterford,J. H.; Colton, R.; O'Donnell, T. A. (Rev. Pure Appl. Chem. 17 [1967]123/32, 127/8). [2] O'Donnell, T. A.; Stewart, D. F. (Inorg. Chem. 5 [1966]1434/7). [3] Canterford, J. H.; O'Donnell, T. A. (Inorg. Chem. 6 [1967] 541/4). Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 163 2.2.8.8.1 Handling and Storage Because of its high reactivity with moisture, MoF6 must be handled in a clean and dry high vacuum system (1), in a dry box [2,3), or in N2 atmosphere (4) at low temperatures. Glass can be used as a material for handling and storage when special precautions are taken to remove traces of H20 and HF which lead to complete hydrolysis of the MoF6 and attack of the glass by a chain reaction (see p. 172) [5 to 7). Usually the clean glass vessels are dried by flaming in vacuum and HF is removed by adding NaF as a "getter" [8 to 12). Borosilicate glass is attacked by liquid MoF6 but can be protected by platinization with H2PtF6 in organic solvents (13). Nickel and monel appear to be the main metallic materials which can satisfactorily be used as containers for handling and storing MoF6 [8,14 to 22). Inconel proved to be more resistant than nickel (23). Corrosion tests with Ni and numerous Ni alloys at 500°C (7 to 9.2 h) showed good resistance against gaseous MoF6 for Inconel, HyMu-80, and INOR-8 (24). At 20 to 60°C (100 to 150 h) Au, Pt, Ni, and stainless steel are suitable metallic materials for handling pure and technical grade MoF6 (13). For large scale handling nickel and copper are proposed as materials (9). Alternative materials for reaction vessels and critical parts are poly(chlorotrifLuoroethylene) (Kel-F) and Teflon, see e.g. [3,20,21,25 to 27) and (28), respectively. However, Kel-F ampules were not suitable for long term storage (22). Good resistance against pure and technical grade MoF6 at 20 to 60°C (100 to 150 h) is also stated for Fluoroplast-4 and leucosapphire (13). Since MoF6 reacts with the usual stopcock lubricants, stopcocks must be lubricated with a fluorochlorocarbon light grease (8) or with fully fluorinated tap grease [5, 9). For prolonged manipulation even fluorinated greases are insufficient and greased taps and tapered joints are replaced by specially designed valves and joints (10). Also packless all-metal valves [10, 29) and Teflon-packed valves (15) are used. Equipment for carrying out reactions is given in [20, 23, 29). References: (1) Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A.; Steven, A. M. (lnorg. Syn. 13 [1971]146/50). (2) McLean, R. R.; Sharp, D. W. A.; Winfield, J. M. (J. Chem. Soc. Dalton Trans. 1972676/8). (3) Levy, J. H.; Taylor, J. C.; Wilson, P. W. (Acta Cryst. B 31 [1975] 398/401). (4) Afanas'ev, M. L.; Gabuda, S. P.; Lundin, A. G.; Opalovskii, A. A.; Khaldoyanidi, K. A. (lzv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 4, pp. 18/22; C.A. 70 [1969] No. 52864). [5) Gaunt, J. (Trans. Faraday Soc. 49 (1953) 1123/31, 1123). [6) Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1563/8). [7) 'Galkin, N. P.; Bogdanov, G. V.; Fedorov, V. D.; Orekhov, V. T. (Zh. Neorgan. Khim. 16 [1971) 496/9; Russ. J. Inorg. Chem. 16 [1971) 262/4). [8) Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951)1164/7). (9) Brady, A. P.; Clauss, J. K.; Myers, O. E. (WADC-TR-56-4 [1955)1/55, 1/2; N.S.A. 10 [1956) No. 7512). [10) O'Donnell, T. A. (J. Chem. Soc. 1956 4681/2). [11) Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4229 [1968) 33/7; N.S.A. 22 [1968) No. 25374). [12) Weaver, C. F.; Friedman, H. A.; Hess, D. N. (ORNL-4254 [1968)129/34; N.S.A. 22 [1968) No.47112). Gmelin Handbaak MaSuppl. Val. 85 11" 164 MoLybdenum Fluorides [13] NiseL'son, L. A.; NikoLaev, R. K.; SokoLova, T. 0.; StoLyarov, V. 1.; KoroLev, Yu. M. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Ser. Khim. Nauk 1968 No. 1, pp. 109/14; C.A. 69 [1968] No. 69834). [14] SettLe, J. L.; Stein, L. (ANL-5959 [1959]136/7; N.S.A. 13 [1959] No. 13360). [15] Osborne, o. W.; Schreiner, F.; MaLm, J. G.; Selig, H.; Rochester, L. (J. Chem. Phys. 44 [1966] 2802/9). [16] Trevorrow, L. E.; SteindLer, M. J.; SteidL, O. V.; Savage, J. T. (ANL-7240 [1960]1/20, 8; C.A. 67 [1967] No. 57717). [17] Trevorrow, L. E.; SteindLer, M. J.; SteidL, O. V.; Savage, J. T. (Advan. Chem. Sero No. 71 [1967] 308/19, 309). [18] Pitts, J. J.; Jache, A. W. (Inorg. Chem. 7 [1968]1661/3). [19] CarLes, M. J.; Aubert, J. (J. Chim. Phys. 67 [1970] 671/5). [20] O'OonneLL, T. A.; Stewart, T. F. (Inorg. Chem. 5 [1966] 1434/7). [21] Paine, R. T.; Asprey, L. B. (Inorg. Chem. 13 [1974]1529/31). [22] NuttaLL, R. L.; Churnay, K. L.; KiLday, M. V. (J. Res. Nat!. Bur. Std. [U.S.] 83 [1978] 335/45, 336). [23] Fukutomi, M.; Corbett, J. o. (J. Less-Common Metals 55 [1977]125/30). [24] Gunther, W. H.; SteindLer, M. J. (ANL-7241 [1966]1/40,23,31; C.A. 68 [1968] No. 34999). [25] FrLec, B.; Hyman, H. H. (Inorg. Chem. 6 [1967]1596/8). [26] Levy, H. J.; Sanger, P. L.; TayLor, J. C.; WiLson, P. W. (Acta Cryst. B 31 [1975]1065/7). [27] Paine, R. T.; Asprey, L. B.; Graham, L.; Ba rtLett , N. (Inorg. Syn. 19 [1979]137/40). [28] NikoLaev, N. S.; Sukhoverkhov, V. F. (Ookl. Akad. Nauk SSSR 136 [1961] 621/3; Proc. Acad. Sci. USSR Chem. Sect. 136/141 [1961]101/3). [29] O'OonneLL, T. A.; Stewart, o. F. (J. Inorg. Nucl. Chem. 24 [1962] 309/14). 2.2.8.8.2 Physical Changes Thermolysis. Thermodynamic caLcuLations of the stabiLity of MoFs at high temperatures show that at 1000 to 2000 K and 1 to 0.001 atm the reaction MoFs(g) -c> MoF4(g) + 2 F(g) is possibLe. The caLcuLated thermaL effect at 298 K is 810 kJ/mol. EquiLibrium constants are Listed in the paper [1]. cf. aLso [2]. The bond dissociation energy 0298(FsMo-F) = 94 kcaLlmoL [15]. Photolysis. The photolysis of MoFs in an Ar matrix at 6±1 K by UV radiation (A~200 nm) proceeds in two steps, the first being the formation of MoFs, which was identified by the IR absorption bands at 693.5 and 658 cm-1. ALso a weaker band at 674 cm-1 was observed which probabLy beLongs to MoF4 formed by the photolysis of MoFs. The photolysis rate va ries with dilution of the MoFs by Ar. Heating the specimen to 35 K leads to recombination via MoFs + F -c> MoFs. The 674 cm-1 band remains unchanged [3]. The multiphoton ionization of gaseous MoFs at lO-s to lO-s Torr by an ArF excimer Laser (193 nm) at intensities of several GW/cm2 causes extensive fragmentation and ionization up to M0 2+. In the mass spectrum mainly Mo+ but also M0 2+ occurs [4]. Isotopically seLective jissociation can be induced by irradiating low pressure (~1 Torr) samples of MoFs with intense CO2 laser radiation. Several frequencies within the weak V3 + Vs combination band were employed. At least two of the Lines, P(10) and P(16), show isotope enrichment. Irradiation on the high-frequency side (P(10)) of the band depletes the Light isotopes while lower frequency irradiation (P(16)) depletes the heavier isotopes. The selectivity is smaLL but significant (~1 % per mass unit) and the reaction yield is substantiaLLy Less than for similar experiments with SFs [5]. see "SchwefeL" Erg.-Bd. 2, 1978, p. 171. The muLtiphoton absorption and the isotopicaLLy selective excitation from IR laser pulses (and thereby the efficiency of the Laser isotope Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 165 separation) is enhanced by raising the temperature of the MoF6 gas from 199 to 500 or 600 K [6]. Isotope-selective IR multiphoton dissociation of MoF6 (2 Torr) with a maximum value for selectivity of 1.1 takes place with parallel beams of a para-H2 Raman laser at 728 cm-1 and - 58°C [7]. Reactions in Electrical Discharges. Dissociation processes in the hollow cathode glow discharge plasma have been investigated for some molecular species, e.g. MoF6. With the discharge mixtures of MoF6 with He or Ar deposit metallic Mo on the cathode surface [8]. Reactions with Electrons. Formation of positive ions. In the mass spectrum of MoF6 gas at 70 eV the following positive ions were observed (98Mo isotope simply denoted as Mo; relative abundances related to MoFt in parentheses): MoFt (100), MoFt (32.5), MoFt (19.9), MoFt (19.0), MoF+ (12.2), Mo+ (9.6), MoF~+ (8.3), MoF~+ (5.9), MoF~+ (5.8), MoF2+ (3.4), M0 2+ (3.0), F+ (6.9). For additional data of the corresponding ionic species containing the less abundant isotopes 92Mo, 9410 97Mo, and 1OOMo see the table in the paper [9]. Earlier measure ments which involve only +1 charged ions summarized for all isotopes are in satisfactory agreement with these data [10]. lonization efficiency curves for positive MoF6 fragment ions are plotted in [11] for electron energies ranging from 16 to 45 eV. For the fragmentation of MoF6 by electron impact according to MoF6 + e- ~ MoFt + F + 2e- the threshold energy was determined to be 15.2 eV [14]. Formation of negative ions. At low incident electron energies the formation of MoF6", MoFs, and F- (at about 0 to 3 eV), and MoF4" (at 4 to 9 eV) occurs. Contrary to other hexafluoride molecules (e.g. UF6 or SF6) the MoF6 forms the negative hexafluoride ion by direct electron attachment at electron energies close to zero [12]. The MoF6 proved to be an excellent electron attacher at high temperatures. By using a jet of partially ionized hot air at T>3000 K and an ambient pressure of 20 Torr with injection of gaseous MoF6 coaxial along the jet centerline the attachment performance exceeds that of SF6 [13]. The electron affinity of MoF6 forming MoF6" has been obtained from various experiments to be 517 ± 6kJ/mol (~5.36 eV) [16], ~5.14 eV [17], and ~4.5 eV [18]. References: [1] Galkin, N. P.; Tumanov, Yu. N. (Termodin. Termokhim. Konstanty 1970 195/9; C.A. 74 [1971] No. 57934). [2] Galkin, N. P.; Tumanov, Yu. N.; Butylkin, Yu. P. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Ser. Khim. Nauk 1968 No. 2, pp. 12/21,18; C.A. 69 [1968] No. 110616). [3] Blinova, O. V.; Predtechenskii, Yu. B. (Opt. Spektroskopiya 47 [1979] 1120/5; Opt. Spectrosc. [USSR] 47 [1979] 622/4). [4] Stuke, M. (Ber. Bunsenges. Physik. Chem. 86 [1982] 837/41). [5] Freund, S. M.; Lyman, J. L. (Chem. Phys. Letters 55 [1978] 435/8). [6] Harn, D. 0.; Tsay, W. S. (U.S. 4303483 [1979/81]; C.A. 96 [1982] No. 76294). [7]' Oyama, T.; Satooka, S.; Kato, S.; Takeuchi, K.; Midorikawa, K.; Tashiro, H. (Reza Kagaku Kenkyu NO.8 [1986] 61/3 from C.A. 10~ [1987] No. 165912). [8] Metyel, A. S.; Nastyukha, A. I. (Proc. 13th Intern. Conf. Phenom. lonized Gases, Berlin 1977, Vo1.1, pp. 379/80; C.A. 89 [1978] No. 121531). [9] Beattie, W. H. (Appl. Spectrosc. 29 [1975] 334/7). [10] Redman, J. D.; Strehlow, R. A. (ORNL-4229 [1968] 37/9; N.S.A. 22 [1968] No. 25374). [11] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970] 116/21, 118). [12] Stockdale, J. A. D.; Compton, R. N.; Schweinler, H. C. (J. Chem. Phys. 53 [1970] 1502/7). [13] Shui, V. H.; Singh, P.I.; Kivel, B.; Bressel, E. R. (AIAA [Am.lnst. Aeron. Astron.] J.17 [1979] 1178/84; C.A. 92 [1980] No. 47356). Gmelin Handbook Mo Suppl. Vol. B 5 166 MoLybdenum Fluorides [14) KLeinschmidt, P. 0.; Lau, K. H.; HiLdenbrand, D. L. (J. Chem. Thermodyn. 11 [1979)765/72). [15) HiLdenbrand, D. L. (J. Chem. Phys. 65 [1976) 614/8). [16) Burgess, J.; Haigh, 1.; Peacock, R. 0.; TayLor, P. (J. Chem. Soc. DaLton Trans. 19741064/6). [17) Compton, R. N.; Reinhardt, P. W.; Cooper, C. D. (J. Chem. Phys. 68 [1978)2023/36, 2028). [18) Mathur, B. P.; Rothe, E. W.; Reck, G. P. (J. Chem. Phys. 67 [1977) 377/81). 2.2.8.8.3 Reactions with Nonmetallic Elements Noble Gases. For solubiLity in Liquid Krsee p. 181. No reaction was observed with Xe [1). The near-IR spectrum of a soLution of MoF6 in Liquid Xe recorded after cooLing to 77 K indicates charge-transfer transitions for MoF6 with Xe. The concomitant charge-transfer compLex is weakLy bound [2). Hydrogen. The reduction of MoF6 by hydrogen takes pLace in steps and invoLves the formation of Lower fluorides among which MoF3 is the most stabLe compound. The finaL reduction product is metallic moLybdenum. A thermodynamic anaLysis of the imaginabLe reduction steps in the temperature range 298 to 1600 K shows that the formation of MoFs, MoF4 , and MoF3 as intermediate products is possibLe whereas MoF2 can not occur [3). At room temperature there is onLy a very sLow reaction but in the presence of UV Light (Hg Lamp) reduction to MoFs in good yieLd occurs after 3 to 5 d [4). The deposition of metallic Mo from gaseous MoF6 + H2 mixtures onto heated substrates takes pLace above 500°C. Thermodynamic data and kinetic studies at 500 to 1200°C indicate that the reaction mechanism is characterized by two main stages: the formation of MoF3 and the H2 reduction of MoF3 to Mo. The MoF3 formation is due to H2 reduction of MoF6 (via MoFs and MoF4) and to the reaction MoF6(g) + Mo(s) ~ 2 MoF3(s) wh ich starts after the formation of a moLybdenum Layer when an inert substrate is used and is significant from the very beginning when Mo is used as a substrate. When Mo is present the Latter reaction is the rate controLling process. In view of the fact that MoFs and MoF4 are reLativeLy unstabLe above 500°C, the chemicaL changes which are possibLe during the reduction of MoF6 to Mo may be written as foLLows [5), see aLso [6): HF H t ~HF ~2!~.2 HF I ! MoF, I MoF6 • ~ I Mo H2 .. MoF 3 -- Mo - HF Enrichment of the gas phase with HF decreases the deposition rate of Mo [7, 8). A quantitative anaLysis of the kinetic characteristics of the heterogeneous reduction of MoF6 by H2 on a moLybdenum substrate summarized in a kinetic equation is presented in [9). The effect of the reduction conditions (e. g. reduction temperature and HF concentration in the gaseous mixture) on the morphoLogicaL and mechanicaL properties of the Mo deposits are described in [10). The hydrogen reduction of MoF6 is wideLy used to produce moLybdenum coatings on various substrates, see "MoLybdän" Erg.-Bd. A 1,1977, pp. 167/72, and [11 to 14, 27). It aLso serves for the deposition of compact moLybdenum on a heated base; for optimum conditions see [15). The technoLogicaL feasibiLity of the process is given in [16). Gmelin Handbook Mo Suppl. Val. B 5 167 For the reaction MoF6(g)+3H2(g)~ Mo(s)+6HF(g) the free energy ßG=-50 kcaUmoL at 400°C has been caLcuLated [27]. For thermodynamic caLcuLations see aLso [17]. The reduction of an MoF6 (5%) + WF6 (95%) mixture by H2 at 500 to 700°C Leads to the simuLtaneous deposition of Mo and W, the aLLoy containing 9 to 12% Mo [18]. For the reduction with H2 in Liquid HF see p. 175. Air. The compound is known to be stabLe in dry air, see "MoLybdän", 1935, p. 150. When Liquid MoF6, in KeL-F (= poLy(chLorotrifLuoroethyLene)) ampuLes, is exposed to air at room temperature, cLear crystaLs assumed to be MoOF4, form above the Liquid after severaL days [19]. For reactions with humid air see p. 170. lodine is readiLy dissoLved by MoF6 without reaction [20]. For reaction with iodine in acetonitriLe see p. 175. Sulfur is unaffected by MoF6 [20]. Carbon. MoF6 can be intercaLated between the Layers of graphite. At 24°C and 523.6 Torr an equiLibrium state is reached after 750 to 800 h. The product obtained corresponds to C5MoF6 [21]. Liquid MoF6 in a moneL ampuLe in contact with graphite at 20°C gives a bLue-bLack second stage intercaLation compound after 48 h corresponding to C22±2MoF6 and a first-stage com pound after one week corresponding to Cll ±lMoF6. Thermogravimetry of the n-th stage intercaLation compounds confirmed the composition C(ll ±1)nMoF6 [22], see aLso [24]. Charge-transfer measurements (refLectivity and Raman spectra, EPR, and magnetic susceptibiLity) in the first-stage intercaLated compound (Cato llMoF6) show that a Large fraction of the intercaLant moLecuLes remain neutraL, the charge transfer per MoF6 moLecuLe is approximateLy 0.2. Thus, the reaction can be formuLated as mC + MoF6~ C~,+(MoF6)x(MoF6)1_x with x=0.2 [23, 28], see aLso [29]. In the presenceof Cr02F2, formation of a 1:1 compLex between Cr02F2 and MoF6 may occur between the graphite Layers (C 15MoCrF70 2) [25]. Silicon. When MoF6 is condensed directLy into Si powder without soLvent present an expLosive reaction may resuLt [26]. Molybdenum films can be deposited by low pressure chemicaL vapor deposition (LPCVD) on silicon substrates by the reduction of MoF6 in an argon atmosphere according to 2MoF6(g)+3Si(s)~2Mo(s)+3SiF4(g). The free energy of this reaction is ßG = - 213 kcaUmol at 400°C [27]. For reaction of MoF6 with Si in Liquid HF see p.175. References: [1] Canterford,J. H.; Colton, R.; O'DonneLL, T.A. (Rev. Pure Appl. Chem. 17 [1967]123/32,127/8). [2] Webb, J. D.; Bernstein, E. R. (J. Am. Chem. Soc. 100 [1978] 483/5). [3] Kopchikhin, D. S.; Rychagov, A. V.; Korolev, Yu. M.; Rakov, E. G. (Tr. Mosk. Khim. Tekhnol. Inst. No. 62 [1969] 60/2; C.A. 75 [1971] No. 80810). [4] Asprey, L. B.; Paine, R. T., Jr. (U.S. 3929601 [1974/75]; C.A. 84 [1976] No. 124096). [5] Korolev, Yu. M.; Rychagov, A. V. (Izv. Akad. Nauk SSSR MetaLLy 1978 No. 6, pp. 16/22; Russ. Met. 1978 No. 6, pp. 14/8). [6] Rychagov, A. V.; Korolev, Yu. M.; Pobedash, N. V. (Met. MetaLLoved. Chist. Metal. No. 11 [1975] 37/47; C.A. 85 [1978] No. 48830). [7] Korolev, Yu. M.; Rychagov, A. V. (Izv. Akad. Nauk SSSR MetaLLy 1980 No. 2, pp. 59/60; Russ. Met. 1980 No. 2, pp. 50/1). [8] Korolev, Yu. M.; Rychagov, A. V. (Met. MetaLLoved. Chist. Metal. No. 13 [1979]32/4; C.A. 93 [1980] No. 76768). [9] Korolev, Yu. M.; Rychagov, A. V. (Izv. Akad. Nauk SSSR MetaLLy 1979 No. 6, pp. 34/42; Russ. Met. 1979 No. 6, pp. 27/36). Gmelin Handbook Mo Suppt. Vot. B 5 168 MOlybdenum Fluorides [10] Korolev, Yu. M.; Rychagov, A. V. (Fiz. Khim. Obrab. Mater. 1979 No. 2, pp. 128/35; C.A. 90 [1979] No. 207803). [11] Jaeger, R. R.; Cohen, S. T. (Proc. 3rd Intern. Conf. Chem. Vapor Deposition, Salt Lake City 1972, pp. 500/12,501; C.A. 84 [1976] No. 36537). [12] Jaeger, R. R.; Cohen, S. T. {MLM-1918 [1972} 1/13, 2; C.A. 77 [1972] No. 133947). [13] Korolev, Yu. M.; Rychagov, A. V. (lzv. Akad. Nauk SSSR Metally 1978 No. 5, pp. 40/6; Russ. Met. 1978 No. 5, pp. 31/6). [14] Watanabe, N.; Chong, Yong-Bo {Denki Kagaku 49 [1981] 784/6 from C.A. 96 [1982} No. 89964). [15] Epshtein, A. L.; Izhvanov, L. A.; Korolev, Yu. M.; Stolyarov, V.I.; Pobedash, N. V. {U.S.S.R. 180800 [1964/66}; C.A. 65 [1966} 11916). [16] Korolev, Yu. M.; Solov'ev, V. F.; Agnokov, T. Sh.; Morozova, O. V. (Khim. Tekhno!. Molibdena Vol'frama 1978 No. 4, pp. 12/21; C.A. 90 [1979] No. 190288). [17] Zakharov, A. A.; Kazantsev, V. V.; Lishnev, L. A. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 117; C.A. 90 [1979] No. 13065). [18] Korolev, Yu. M.; Solov'ev, V. F.; Ponomareva, A. M.; Emet'yanov, A. B.; Gurovich, N. A. {Met. Metalloved. Chist. Meta!. No. 13 [1979] 22/8; C.A. 93 [1980} No. 76767). [19] Nuttall, R. L.; Churney, K. L.; Kilday, M. V. (J. Res. Nat!. Bur. Std. [U.S.]83 [1978]335/45,337). [20] O'Donnell, T. A.; Stewart, D. F. (J. Inorg. Nuc!. Chem. 24 [1962] 309/14, 310). [21] Opalovskii, A. A.; Kuznetsova, Z. M.; Chichagov, Yu. V.; Nazarov, A. S.; Uminskii, A. A. (Zh. Neorgan. Khim. 19 [1974] 2071/3; Russ. J. Inorg. Chem. 19 [1974]1134/6). [22] Hamwi, A.; Touzain, P.; Bonnetain, L. (Mater. Sci. Eng. 31 [1977] 95/8). [23] Ohana, 1.; Vaknin, D.; Selig, H.; Yacoby, Y.; Davidov, D. (Phys. Rev. B Condens. Matter [3] 35 [1987] 4522/5). [24] Hamwi, A.; Touzain, P. (Rev. Chim. Minerale 19 [1982] 432/40). [25] Hamwi, A.; Touzain, P.; Bonnetain, L. (Rev. Chim. Minerale 19 [1982]651/62, 655). [26] Paine, R. T.; Asprey, L. B. (lnorg. Chem. 13 [1974]1529/31). [27] Lifshitz, N.; WiUiams, D. S.; Capio, C. D.; Brown, J. M. (J. Electrochem. Soc. 134 [1987] 2061/7); Lifshitz, N.; Green, M. L. (Proc. Electrochem. Soc. 87-8 [1987] 677/84). [28] Vaknin, D.; Davidov, D.; Selig, H.; Yeshurun, Y. (J. Chem. Phys. 83 [1985] 3859/62). [29] Kjems, J. K.; Vaknin, D.; Davidov, D.; Selig, H.; Yeshurun, Y. (Syn. Metals 23 [1988]113/9). 2.2.8.8.4 Reactions with Metals Collisional ionization in orthogonal crossed beams of Na atoms and MoF6 yields the ions MoFs, MoFs, MoF4, and F- with thresholds for ion production at ~O, 5.7, 12.4, and 10.0 eV, respectively (target gas at room temperature). The MoFs ions are only formed in the presence of an ionizing filament (~1900 K). For collisions with K atoms at 25 eV (center of mass, c.m.) the relative intensities (in parentheses) are: MoFs (1), MoFs (10), MoF4 (4), and F- (10), and with Cs atoms at 10 eV (c.m.) MoFs «1), MoFs (10), F- (1.4). With Cs atoms both MoFs and MoFs were observed at ~5.2 eV (c.m.) and MoF4 above ~15 eV (c.m.) [1].lonization at thermal energies proceeds with the alkali dimers but not with the alkali atoms. With thermal Cs atoms the product ions are CS+, MoFs, and MoFs (intensity ratio MoFs /MoFs = 0.6) resulting from the reactions CS2+MoF6~CS++CsF+MoFs and CS2+MoF6~CS++Cs+MoFs. With K atoms an additional positive ion, K2F+, forms (K2F+/K+ = 0.3) presumably from K2 + MoF6 ~ K+F-K+ + MoFs' Experiments were also done with an eV-range Cs beam [2,3]. For molecular beam studies with thermal K and Cs atoms see also [4}. The total cross sections are 0.49 and 2.2 N for the ionization reactions with K2 and Cs2, respectively [5]. Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 169 Mercury reacts in contact with MoF6 [6]. Mo metal reacts with MoF6 al ready at temperatures below 100°C to form MoF5 as the main reaction product. This reaction is the most important route for preparing MoF5, see p. 94. During the reduction in a reactor with molybdenum heating filaments, MoF5, MoF4 , and MoF3 are produced. The reduction to form MoF5 starts at filament temperatures 150 to 200°C at a pressure of 10-2 to 10-3 atm. MoF4 occurs at 300 to 400°C filament temperature at 0.5 to 0.6 atm, and MoF3 above 600°C at 0.5 to 0.6 atm [7], cf. also pp. 74 and 86. Quantitative reduction to MoF3 occurs when a stream of gaseous MoF6 in Ar reacts with molybdenum metal at 550 to 600°C [8]. The reaction MoF6(g) + Mo(s)~2MoF3(S) is of importance in the deposition of metallic Mo from MoF6+ H2 mixtures, see p. 166. The composition of the vapor resulting from the reaction of MoF6 with Mo in a Knudsen cell at 75 to 850°C, was determined as follows [9, 10]: gaseous compound vaporcomposition (in %) attemperatures(in °C) 75 200 450 650 750 850 MoF6 100 62 11 8 9 11% MoF5 38 89 81 62 38 MoF4 11 29 51 When gaseous MoF6 is admitted to an Mo effusion cell packedwith Mo wire, the ionic species MoFt, MoF:, and MoFj appear in the mass spectrum of the effusing vapor at temperatures above 1000 K, while temperatures of 1700 K and more are r,equired to generate Mo+, MoF+, and MoFt. From the magnitudes of the appearance potentials it was concluded that each of these ions is formed by simple ionization of the corresponding parent molecule [11]. From equilibrium measurements of the reaction 5/6 MoF6(g) + 1/6Mo(s)~MoF5(g) at 460 to 525 K by mass spectrometric analysis of the effusion vapor, the enthalpy of the reaction at 298.15 K, ßH"/R = 6.9 ± 0.5 and 6.4 ± 1.0 kK was derived using the 2nd and 3rd law, respective ly. Equilibrium constants are listed in the paper [12]. MoF6 is reduced to MoF5 on a hot filament of tungsten [13]. Platelets of nickel, gold, platinum, and stainless steel are stable against pure or technical grade MoF6 at 20 to 60°C for periods up to 150 h, the weight loss being less than 0.1 g/(m2 ·d). Silver is less resistant; at 20°C the weight loss is 30 to 40 g/(m2 ·d) [14]. For the stability of metallic materials in contact with MoF6 see also p. 163. For reactions with metals in nonaqueous solutions see p. 175. References: [1] Compton, R. N.; Reinhardt, P. W.; Cooper, C. D. (J. Chern. Phys. 68 [1978]2023/36, 2028, 2031). [2] Rothe, E. W. (COO-2850-2 [1977]1/22, 5, 8,13; C.A. 88 [1978J No. 110896). [3] Mathur, B. P.; Rothe, E. W.; Reck, G. P. (J. Chem. Phys. 67 [1977] 377/81). [4] Annis, B. K.; Datz, S. (J. Chem. Phys. 66 [1977] 4468/77, 4472). [5] Wells, G. J.; Reck, G. P.; Rothe, E. W. (J. Chem. Phys. 73 [1980]1280/5). [6] O'Donnell, T. A. (J. Chem. Soc. 19564681/2). [7] Pervov, V. S.; Butskii, V. D.; Podzolko, L. G. (Zh. Neorgan. Khim. 23 [1978]1486/91; Russ. J. Inorg. Chem. 23 [1978] 819/22). [8] Fukutomi, M.; Corbett, J. D. (J. Less-Common Metals 55 [1977] 125/30). [9] Redman, J. D.; Strehlow, R. A. (ORNL-4229 [1968] 37/9; N.S.A. 22 [1968] No. 25374). [10] Strehlow, R. A.; Redman, J. D. (ORNL-4254 [1968]134/6). Gmelin Handbook Mo Suppt. Vol. B 5 170 Molybdenum Fluorides [11] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [12] Kleinschmidt, P. D.; Lau, K. H.; Hildenbrand, D. L. (J. Chem. Thermodyn. 11 [1979]765/72). [13] Falconer, W. E.; Jones, G. R.; Sunder, W. A.; Haigh, 1.; Peacock, R. D. (J. Inorg. Nucl. Chem. 35 [1973] 751/3). [14] Nisel'son, L. A.; Nikolaev, R. K.; Sokolova, T. D.; Stolyarov, V. 1.; Korolev, Yu. M. (lzv. Sibirsk. Otd. Akad. NaukSSSRSer. Khim. Nauk1968 No. 1, pp. 109/14, 110; C.A.69 [1968] No. 69834). 2.2.8.8.5 Reactions with Inorganic Compounds Hydrolysis MoF6 is rapidly hydrolyzed by water. It fumes in the presence of water vapor [1, 51], and as a result of hydrolysis a blue coloration appears when gaseous MoF6 comes into contact with humid air [2], forming a blue highly viscous liquid [51]. The reaction with moisture proceeds violently, sometimes causing the explosion of a sample [3]. The hydrolysis in anhydrous HF with a controlled amount of water, which is somewhat less than that required for a stoichiometric reaction to yield MoOF4, gives only the solid MoOF4 as is the case with a mole ratio of MoF6: HP =1:1 [4]. Vibrational spectra indicate that, contrary to the behavior of WF6, H30+MoP2F9 does not form [5]. Likewise, the formation of MoOF4 as the only product of hydrolysis was deduced from electrochemical investigations of MoF6 in anhydrous HF on addition of H20 at mole ratios H20: MoF6 =1 :1 up to 2:1, see p. 195. Based on studies of the MoF6-HF-H20 system (see p. 206), with increasing H20 content in the solution the solid hydrolysis products are MoOF4·2.5H20, Mo02F2·2Hp, and Mo03·H20 [6,7]. With excess water an ill-defined product forms which shows no Mo-F stretching vibrations in the Raman spectrum [4]. The hydrolysis constant Khyd =3x103 assigned to MoF6+2H20 ~ Mo02F2+ 4 HF was determined from the changes in the electrical conductivity at - 5°C of solutions of MoF6 in HF on addition of water [8]. In aqueous NaOH the hydrolysis proceeds according to MoF6 + 80W ~ MoO~- + 6 F- + 4 H20. For the enthalpy of hydrolysis of gaseous MoF6 in 1 or 0.1 M NaOH solutions a mean value of ßHhYd =-732(4) kJ/mol was determined [9]. For liquid MoF6 in 0.1075M NaOH solution ßHhYd.29S=-154.7 kcaUmol (~-647.3 kJ/mol) [10,11]. In aqueous NaOH of concen trations between 0.302 and 0.718N values for ßHhYd.29S between -716.09 ancl -724.81 kJ/mol were measured. Combining these values with the calorimetrically determined enthalpies of solution for Mo03(s) in NaOH solution, NaF(s) in Mo03 + NaOH solution, and NaF(s) in H20(I), the enthalpy of the reaction MoF6(l) + 60W(aq) ~ Mo03(s) + 6 F-(aq) + 3 H20(I) in infinitely dilute NaOH solution, ßHhYd.29S.15 =-641.23 kJ/mol (uncertainty interval +1.8, - 4.0 kJ/mol) [12]. Nonmetallic Compounds Nitrogen Compounds. With liquid NH3 at - 35 to - 78°C a dark brown solid product of composition (NH3)5MoF6 forms wh ich is considered as a mixture of MoF5· 4 NH3 and NH4F. In the solid phase above -130°C reduction of MoF6 to MoF5 by NH3 in an exothermic reaction takes place [14]. Explosive reaction with anhydrous hydrazine occurs already at temperatures below - 80°C. By slowly bubbling a gaseous mixture of MoF6 and Ar through liquid N2H4 at O°C a dark solution forms, with increasing concentration of MoF6 a rapid reaction starts evolving gases and leading to an explosion [13]. Tetramethylammoniumazide, (CH3)4NN3, dissolved in anhydrous S02, reacts with MoF6 at room temperature with evolution of N2. After removal of all volatile materials in vacuum, Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 171 (CH3)4NMoVFs remains. With trimethyLsiLyLazide. (CH3hSiN3• at room temperature trimethyLsiLyL fluoride and nitrogen form. but at - 70°C. MoFsN3 and cis-MoF4(N3)2 resuLt [53]. A yeLLow solid. assumed to be MoFsN3• which decomposes at -10°C. forms by the reaction of (CH3hSiN3 with excess MoFs in Genetron (C2CL3F3) soLution [54]. N20 does not react with MoFs at 25 or 60°C (4 to 24 h) at a totaL pressure of 200 Torr. With NO in excess the soLid nitrosyLium hexafLuoromoLybdate(V). NOMoFs• is formed at 25 or 60°C in a rapid and quantitative reaction [15. 16]. Gaseous N02 does not react with MoFs at 25°C and pressures up to 50 Torr. Formation of a white soLid product was observed at 60°C and 100 Torr and was attributed to reaction with the N20 4 species [17]. which can be represented by MoFs(g) + N20 4(g) ~ NOMoOFs(s) + N02F. The same soLid product forms with the Liquid com pound when MoFs (0.Q185 moL) is mixed with N20 4 (0.0612 moL) in an evacuated reactor at Liquid nitrogen temperature and then heated to 25°C. In addition. N02F. NOF. and N20 S form as the gaseous products [18]. For reactions with NOF. N02F. and NOCL see beLow. Halogen Compounds. Studies of the XeF2-MoFs system by DTA indicate the formation of the congruently meLting compound XeF2· MoFs and an incongruently meLting compound of approximate composition XeF2·4MoFs [19]. see aLso p. 188. On treating 02F2 with MoFs (presumabLy at temperatures between 110 and 190 K) a white solid of approximate composition 02MoF7 forms in Low yieLd (the reaction is said not to be reproducibLe) [20]. CLF3 and BrF3 do not react with MoFs [21]. Mixtures of SF4 and MoFs give an intenseLy yeLLow soLid beLow - 40°C which decomposes above this temperature [22]. No reaction takes pLace with SF 4 at room temperature and with SeF 4 up to 150°C in a seaLed tube. The reaction with PF3 yieLds PFs and MoFs under conditions ranging from excess MoFs to excess PF3. In the first case. MoFs is present as a soLution in MoFs• whiLe with excess PF3. MoFs forms as a yeUow solid. This reaction is suitabLe for preparing MoFs (see p.95) [23]. Long exposure of MoFs to AsF3 resuLts in the appearance of a bLue coLoration. probabLy caused by the formation of some Mov [24]. A thermodynamic anaLysis of the reaction 2 MoFs(g) + AsF3(L) ~2MoFs(g) + AsFs(g) gives ~H298 = 59.3 kcaL and ~S298 =16 caVK [25]. No reaction takes pLace with AsF3 or SbF3 up to 150°C or with BiF3 at 80°C in seaLed ampuLes [23]. NitrosyL and nitryLfLuoride. NOF and N02F. combine with MoFs at room temperature in a 1:1 moLe ratio to form the white solid compounds NOMoF7 and N02MoF7• respectiveLy [17. 26], see aLso [21]. MoFs reacts rapidLy with numerous chLorides to repLace some or aLL of its fLuorine atoms by chLorine. The foLLowing products are obtained when MoFs and the corresponding chLoride are condensed at -196°C and then warmed to room temperature and maintained there untiL compLetion of the reaction: reactant products of reaction Ref. with excess MoFs with excess chLoride BCL3 M02CL3Fsa). BF3• BCLF2• BCL2F [27] SiCL4b) M02CL3 Fs• SiF4 [27.28] PCL3 M02CL3 Fs• MoFs• PFs• CL2 [23.27.28] AsCL3 M02CL3Fs• AsF3• CL2 [23. 27] SbCL3 M02ClsFs• SbCL2F3 [23. 27] a) ~(Mo!i'Clg)(MovFsh- - b) SLow reaction. Gmelin Handbook Mo Suppl. Vol. B 5 172 Molybdenum Fluorides The initial reaction between the chlorides and MoFs proceeds analogously as demonstrated with PCl3 where MoFs+2PCI3~MoCls+2PF3+0.5CI2' Secondary reactions occur inmany cases. e. g. the MoCl5 reacts with excess MoFs yielding Cl2 and a mixed halide of molybdenum of empirical composition M02Cl3Fs wh ich can be formulated as (Mo!{'Clg)(MoVFsh [23. 27]. Nitrosylchloride. NOCI. reduces MoFs at 25°C to the nitrosylfluoride of Mov. NOMoFs• with evolution of chlorine gas. NOF could not be detected as an intermediate product. Thus. the reaction is assumed to proceed by ionic dissociation of NOCI via transfer of a chloride ion to the MoFs forming the unstable MoFsCI- wh ich dissociates to the chlorine radical and MoFS [17.26]. In the reaction between MoFs and PBr3 both PF3 and PF5 are detected in the volatile reaction products. This is consistent with the following se ries of reactions. each of which is known to occur readily: MoFs+2PBr3~MoBr3+1.5Br2+2PF3; PF3+Br2~PF3Br2; 5PF3Br2 ~3PF5+2PBr5; PBr5~PBr3+Br2 [27]. Other NonmetaLLic Compounds. Oxygen-fluorine exchange between BP3 and MoFs takes place at room temperature according to 3MoFs{g)+B203{S)~3MoOF4{S)+2BF3{g) and af fords the preparation of MoOF4 (see p. 195). The standard enthalpy change for this reaction was calculated as L\H r =-405 kJ/mol {29]. MoFs reacts at room temperature with B(OTeF5h to give BF3 and compounds of composi tion MoF n{OTeF5)s-n which by internaL fluorination and rearrangements yieLd MoOF n{OTeF5)4-n' With an initial mole ratio MoFs: B{OTeF5h = 3:1 at 80°C. MoOF4 forms. presumabLy via MoF5{OTeF5) [50]. SiH4 and Si2Hs react with MoFs at 150°C under reduced pressure forming MoSi2 which can be deposited as a thin film on a suitable substrate [52]. Pure dry MoFs remains unchanged in contact with Si02• glass. or Pyrex for periods of severaL months at room temperature. see. e. g. [30.31]. The weight loss of quartz glass in pure MoFs is 0.5 to 1.0 g/{m2. d) at 20 to 60°C [32]. In the presence of small traces of H20 (anaLogousLy as observed with UFs [33]) a chain reaction starts Leading to complete fluorination of the Si02. In the first step MoFs hydrolyzes readily to the oxide fluoride liberating HF which reacts with Si02 to form SiF4 and Hp. The HP is again involved in the cycLe. The reaction can be broken by absorbing the HF on NaF or KF [34]. This chain reaction is also initiated by traces of HF which is a main contaminant of MoFs preparations. Therefore special precautions are necessary for handling the hexafluoride in contact with quartz [30. 31]. see also p. 163. The reaction of Si02 in the presence of HF can be used for the preparation of MoOF4• see p. 195. Metal Compounds Oxides. The reaction of Cr03 with MoFs at 125°C which yieLds volatiLe Cr02F2 and soLid MoOF4 is a successful route to prepare the molybdenum oxide fluoride. see p. 195 [36]. Reacting MoFs with Mo03 at temperatures above 100°C forms MoOF4. see p. 194. Fluorination of Th02 by MoFs yieLding ThF4 (and Mo03) is one of the sources of fluorine contamination during the deposition of molybdenum onto Th02 particles by hydrogen reduc tion of MoFs. A similar reaction takes place with PU02 forming PuF3 [35]. Fluorides. The reaction of MoFs with NH4F was studied at temperatures ranging from 25 to 70°C with areaction period of 1 h in each case. At 35 to 40°C. NH4MoF7 forms as a transparent solid. Above 30°C the MoFs is partly reduced to MoF5 and NH4HF2 forms. When the mixture is quickLy heated to temperatures between 30 and 45°C. {NH4HF2hMoF5 forms in the reaction product. At 55°C. reduction of MoFs with simuLtaneous complex formation yields NH4MoFs Gmelin Handbook Mo Suppl. Val. B 5 173 while NH 4 MoF7 is present as a by-product. At 60 to 70°C, only NH4MoFs forms. At 70°C at a mole ratio 1:1 of the reactants small amounts of NH 4MoFs were also detected [37]. With LiF the compound Li2MoFa forms in a reversible reaction. The absorption of the gaseous MoFs on the finely divided LiF at 760 Torr has a maximum at 100 to 140°C; above 250°C the reaction product decomposes [38]. Gaseous MoFs is strongly absorbed on NaF at 100°C [39 to 41] to give the white solid complex Na2MoFa. The reaction is reversible at higher temperatures [42] and only very little absorption is stated to occur at 200°C [41]. At apressure of 760 Torr the maximum absorption of MoFs on NaF is at 140 to 160°C while decomposition of the Na2MoFa predominates above 180°C. Formation of NaMoF7 as a superficial reaction product is assumed to occur at high MoFs pressure (e.g. 2 atm) [38]. With high surface area NaF, prepared by decomposition of NaF· HF, the reaction proceeds with the highest rate between 160 and 185°C at 110 to 120 Torr [43]. However, when the NaF was produced by decomposing Na2UFa, the absorption of MoFs proceeds very rapidly even at lower temperatures and leads to products with MoFs: NaF mole ratios of 1:2 and 1:1 (Na2MoFa and NaMoF7 , respectively) [44]. From MoFs containing some bromine, only a negligible amount of the hexafluoride is absorbed on NaF whereas with KF, RbF, or CsF solid products of composition M2MoFa (M = alkali metal) form, which on a second treatment with MoFs undergo no change in weight [45]. Thermographic studies of mixtures of MoFs with KF, RbF, or CsF show great tendencies of these fluorides to form complexes of the type MMoF7 [46]. No reaction takes place between MoFs and BaF2 at 90 to 200°C [38]. Oxidation of WF4 by MoFs at room temperature yields WFs and MoFs [27]. Liquid-vapor equilibrium studies of MoFs-WFs mixtures give evidence for the existence of an almost ideal system [32]. UF3 and UF4 are rapidly oxidized by MoFs in molten LiF + BeF2 mixtures [47]. The MoFs-UFs system is described in "Uran" Erg.-Bd. C 8, 1980, p.275. Chlorides and Bromides. In the alkali and alkaline-earth chlorides, MICI (MI = Li, Na, K, Rb, Cs) and M"CI2 (M" = Be, Mg, Ca, Sr, Ba), the chlorine is rapidly replaced by fluorine when MoFs is condensed onto the corresponding chloride (in excess) at -196°C and then the mixture is warmed to room temperature. In addition to MIF and M"F2, respectively, M02Cl3Fs (-{M01VCI9) (MoVFsh) and Cl2 form [48]. Under similar conditions, TiCl4 is fluorinated to TiF4 by MoFs, regardless of the initial proportions of the reagents. Additionally M0 2Cl3Fs forms with excess MoFs while MoCls and C12 are produced with excess chloride [27]. The orange-colored M02Cl3Fs and C12 are obtained when MoFs and MoCls are mixed at room temperature [28]. MoFs and MoBr4 at mole ratio 2:1 react at room temperature to give the red-brown MoBrF4 as the only nonvolatile product. At other ratios of the reactants traces of other bromide fluorides are formed [49]. Per reactions with metal halides in solution see the next section. Carbonyl Compounds. The reaction with Mo{CO)s or W{CO)s which yields MoFs and MoF4 can be used for the preparation of the pentafluoride (see p.95). When MoFs reacts with Mo{CO)s in the presence of bromine in a nitrogen atmosphere at room temperature, solid MoBrF4 forms together with volatile COFBr, CO, and traces of MoBr4F2 [49]. Gmelin Handbook Mo Suppl. Vol. B 5 174 MoLybdenurn Fluorides References: [1) Gaunt, J. (Trans. Faraday Soc. 49 [1953) 1122/31, 1123). [2) Shustov, L. D.; NikoLenko, L. N.; Senchenkova, T. M. (Zh. Obshch. Khirn. 53 [1983)103/5; J. Gen. Chern. [USSR) 53 [1983) 85/6). [3) Krause, R. F., Jr.; DougLas, T. B. (J. Chern. Therrnodyn. 9 [1977)1149/63, 1151). [4) SeLig, H.; Sunder, W. A.; Schilling, F. C.; FaLconer, W. E. (J. FLuorine Chern. 11 [1978) 629/35, 631). [5) Hoskins, B. F.; Linden, A.; O'DonneLL, T. A. (Inorg. Chern. 26 [1987)2223/8,2224,2227). [6) NikoLaev, N. S.; OpaLovskii, A. A. (Zh. Neorgan. Khirn. 4 [1959)1174/83; Russ. J. Inorg. Chern. 4 [1959) 532/6). [7) NikoLaev, N. S.; OpaLovskii, A. A. (Izv. Sibirsk. Otd. Akad. NaukSSSR 1959 No. 12, pp. 49/58; C.A. 1960 11790). [8) NikoLaev, N. S.; VLasov, S. V.; BusLaev, Yu. A.; OpaLovskii, A. A. (Fiz. Khirn. AnaLiz. Tr. YubiLeinoi Kont., Novosibirsk 1960 [1963), pp. 97/103, 102; C.A. 62 [1965) 4673; Izv. Sibirsk. Otd. Akad. Nauk SSSR 1960 No. 10, pp. 47/56; C.A. 1961 12014). [9) Burgess, J.; Haigh, 1.; Peacock, R. D. (J. Chern. Soc. DaLton Trans. 1974 1062/4). [10) Brady, A. P.; CLauss, J. K.; Myers, O. E. (WADC-TR-56-4 [1955)1/55, 22; N.S.A. 10 [1956) No. 7512). [11) Myers, O. E.; Brady, A. P. (J. Phys. Chern. 64 [1960) 591/4). [12) NuttaLL, R. L.; Churney, K. L.; KiLday, M. V. (J. Res. Nat!. Bur. Std. [U.S.)83 [1978)335/45). [13) FrLec, B. (Inst. Jozef Stetan IJS Rept. R-611 [1972)1/11,5; C.A. 79 [1973) No. 26692). [14) OpaLovskii, A. A.; BLokhina, G. E. (Izv. Vysshikh Uchebn. Zavedenii Khirn. Khirn. TekhnoL. 15 [1972)1617/9; C.A. 78 [1973) No. 66436). [15) Geichrnan, J. R.; Srnith, E. A.; Trond, S. S.; OgLe, P. R. (Inorg. Chern. 1 [1962) 661/5). [16) OgLe, P. R.; Geichrnan, J. R.; Trond, S. S. (GAT-T-552 Pt. 1 [1959)1/5; N.S.A. 16 [1962) No. 4156). [17) Geichrnan, J. R.; OgLe, P. R.; Swaney, L. R. (GAT-T-809 [1961)1/8, 3, 5/7; N.S.A.15 [1961) No. 7238). [18) Geichrnan, J. R.; Srnith, E. A.; Swaney, L. R.; OgLe, P. R. (GAT-T-970 [1962)1/9; C.A. 61 [1964)12940). [19) Legasov, V. A.; Marinin, A. S. (Zh. Fiz. Khirn. 46 [1972) 2649/51; Russ. J. Phys. Chern. 46 [1972) 1515/6). [20) Bantov, D. V.; Sukhoverkhov, V. F.; MikhaiLov, Yu. N. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khirn. Nauk 1968 No. 1, pp. 84/7; C.A. 69 [1968) No. 83077). [21) Canterford, J. H.; Colton, R.; O'DonneLL, T. A. (Rev. Pure AppL. Chern. 17 [1967)123/32, 127/8). [22) BartLett, N.; Robinson, P. L. (J. Chern. Soc. 1961 3417/25,3423). [23) O'DonneLL, T. A.; Stewart, D. F. (J. Inorg. NucL. Chern. 24 [1962) 309/14). [24) Hargreaves, G. B.; Peacock, R. D. (J. Chern. Soc. 19584390/3). [25) GaLkin, N. P.; Turnanov, Yu. N.; Butylkin, Yu. P. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khirn. Nauk 1968 No. 2, pp. 12/22,20; C.A. 69 [1968) No. 110616). [26) Geichrnan, J. R.; Srnith, E. A.; OgLe, P. R. (Inorg. Chern. 2 [1963)1012/5). [27) O'DonneLL, T. A.; Stewart, D. F. (Inorg. Chern. 5 [1966) 1434/7). [28) Stewart, D. F.; O'DonneLL, T. A. (Nature 210 [1966) 836). [29) Burns, R. C.; O'DonneLL, T. A.; Waugh, A. B. (J. FLuorineChern.12 [1978)505/17, 507, 510). [30) O'DonneLL, T. A. (J. Chern. Soc. 1956 4681/2). [31) Weaver, C. F.; Friedrnan, H. A.; Hess, D. N. (ORNL-4254 [1968)129/34, 129; N.S.A. 22 [1968) No.47112). Gmelin Handbook Mo Suppl. Vol. B 5 MoF6 175 [32] NiseL'son, L. A.; Nikolaev, R. K.; Sokolova, T. D.; Stolyarov, V. 1.; Korolev, Yu. M. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No.1, pp. 109/14; C.A. 69 [1968] No. 69834). [33] Grosse, A. V. (MDDC-1038 [1947]1/2). [34] Tanner, K. N.; Duncan, A. B. F. (J. Am. Chem. Soc. 73 [1951]1164/7). [35] Jaeger, R. R.; Cohen, S. T. (MLM-1918 [1972]1/13; C.A. 77 [1972] No. 133947; Proc. 3rd Intern. Conf. Chem. Vapor Deposition, Satt Lake City 1972, pp. 500/12; C.A. 84 [1976] No. 36537). [36] Green, P. J.; Gard, G. L. (inorg. Chem. 16 [1977]1243/5). [37] Opalovskii, A. A.; Blokhina, G. E. (izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. 1971 No. 5, pp. 60/5; C.A. 77 [1972] No. 28370). [38] Peka, 1.; Sykora, F.; Vachuska, J. (Collection Czech. Chem. Commun. 34 [1969]2857/64; C. A. 72 [1970] No. 8819). [39] Brooksbank, W. A., Jr.; Carter, R. J.; Osborne, M. F. (ORNL-2614 [1958]148/50; N.S.A. 13 [1959] No. 2275). [40] Brooksbank, W. A., Jr.; Carter, R. J.; Osborne, M. F. (CF-58-6-86 [1958]1/22, 16; N.S.A. 12 [1958] No. 13008). [41] Krause, J. H.; Potts, J. D. (TlD-11398 [1960]1/50, 39, 41/2; N.S.A. 15 [1961] No. 7412). [42] Kuhrt, W.; Kreutz, R.; Massonne, J. (Kerntechnik 13 [1971]17/20). [43] Katz, S. (inorg. Chem. 3 [1964]1598/600). [44] Katz, S. (inorg. Chem. 5 [1966] 666/8). [45] Cox, B.; Sharp, D. W. A.; Sharpe, A. G. (J. Chem. Soc. 1956 1242/4). [46] Nikolaev, A. V.; Opalovskii, A. A.; Fedorov, V. E. (Therm. Anal. Proc. 2nd Intern. Conf., Wo rcester, Mass., 1968 [1969], Vol. 2, pp. 793/810,799/800; C.A. 73 [1970] No. 94206). [47] Weaver, C. F.; Friedman, H. A. (ORNL-4191 [1967]143/4). [48] O'Donnell, T. A.; Wilson, P. W. (Australian J. Chem. 21 [1968]1415/9). [49] Mercer, M.; Ouellette, T. J.; Ratcliffe, C. T.; Sharp, D. W. A. (J. Chem. Soc. A 1969 2532/4). [50] Schröder, K.; Sladky, F. (Z. Anorg. Allgem. Chem. 477 [1981] 95/100). [51] Lifshitz, N.; Williams, D. S.; Capio, C. D.; Brown, J. M. (J. Electrochem. Soc. 134 [1987] 206117, 2062). [52] Gaczi, P. J. (Eur. Appl. 245934 [1987] 1/12; C.A. 108 [1988] No. 29876). [53] Glavincevski, B.; Brownstein, S. (Inorg. Chem. 20 [1981] 3580/1). [54] Fawcett, J.; Peacock, R. D.; RusselI, D. R. (J. Chem. Soc. Datton Trans. 19802294/6). 2.2.8.8.6 Reactions with Elements and Inorganic Compounds in Nonaqueous Solutions MoF6 is reduced to MoF5 by hydrogen in anhydrous HF at room temperature in a slow (3 d) and inefficient reaction [1]. Iodine is oxidized by MoF6 in CH 3CN at ambient temperature forming a white solid of composition [I'(NCCH3)2][MoVF6] [2]. Silicon powder frozen in anhydrous HF reacts with MoF6 in HF at moLe ratio Si: MoF6 =1:4 in a typical one-electron reaction to give MoF5 and SiF4. At 23°C the reaction is complete after 1 h [1] and proceeds smoothly to completion in the presence of Pt gauze [3]. At a mole ratio 1 : 2 after 3 d of stirring at 23°C a green oil (M02Fg ?) is obtained. The mechanism of the Si reduction of MoF6 is not clearly understood. It has been suggested that areaction Si +4HF ~SiF4 +4H may be involved and nascent hydrogen could be the effective reducing agent. Preliminary resutts, however, indicate that in the absence of a metal fluoride the rate of hydrogen production is slow [1]. Gmelin Handbook Mo Suppl. Vol. B 5 176 Molybdenum Fluorides Foils, wires, or freshly cut pieces of the metals Zn, Cd, Hg, Tl, Cu, and Ag react rapidly with excess MoF6 in CH 3CN at room temperature, whereas only a slow reaction takes place with Pb, Mn, Ni, and Co. The reaction products isolated after removal of the CH 3CN are nonvolatile solid metal hexafluoromolybdates(V) of compositions M[MoF6h·5CH3CN (M=Zn, Cd, Cu, Co), M[MoF6h·4CH3CN (M = Hg, Ag), and Cu[MoF6]·4CH3CN. In the case of thallium, TtiTllII[MoF6k2CH3CN forms when the mole ratio of the reactants is Tl:MoF6=1:2, and Tl[MoF6k6CH3CN when a large excess of MoF6 is used.ln the presence of moisture, Ag gives a yellow compound, probably AgIiMovOF5 ·4CH3CN. The role of the acetonitrile, in addition to providing a suitable dielectric medium, is in the solvation of the metal cations. As was demonstrated with the products of the Tl, Cu, and Ag reactions, the coordinated CH 3CN can readily be replaced by pyridine but is not removed by pumping [4]. For the reaction with silver cf. also [5]. Later the formation of Agil complexes could not be repeated. Under careful exclusion of moisture the complex [Agl(NCCH3bHMoVF6] forms independently of the stoichio metry up to MoF6:Ag=10:1 [21]. Fe metal is oxidized by MoF6 in CH 3CN to yield the solvated iron(Il) cation [Fe(NCCH3)6F+. The reaction is complicated by solvent attack [19]. A study of the reactions with Cu and Tl metal in CH 3CN under carefully controlled conditions combined with cyclic voltammetry confirmed the order of the oxidizing ability UF6> MoF6> WF6 at 298 K [6]. A CH 3CN solution of MoF6 reacts vigorously with N2H4 dissolved in CH 3CN to evolve nitrogen and NH3 and to possibly form binary lower molybdenum fluorides [7]. The reaction with hydrazinium fluoride, N2H6F2, in anhydrous HF is fast at room temperature and yields a yellow compound of composition N2H6(MoF6b and N2. In the presence of excess N2H6F2 the reaction proceeds further yielding brown hydrazinium hexafluoromolybdate(IV), N2H6MoF6. The second reaction, however, is much slower and is complete only after several days at room temperature [8,9]. Studies of the MoF6-HF-NH4F system at O°C indicate the formation of solid phases NH4F· 2 MoF6 and NH4F· MoF6 at NH4F concentrations in the liquid phase of 2.46 to 20.42 and 21.92 to 29.28 wt%, respectively. The solid phases easily lose MoF6 on drying to give NH4F·1.25MoF6 and NH4F·0.5MoF6, respectively [10]. Solutions of MoF6 in HF are able to dissolve NaF and AgF. With AgF in excess a white compound precipitates and with CuF2 a bright yellow one [11]. When dry NH4F is added gradually at dry-ice temperature to a solution of MoF6 in ClF3 a precipitate of NH4MoF7 forms. Analogously, CsF dissolved in ClF3 reacts with MoF6 in ClF3 to form solid CsMoF7 [12]. In IF5 with the corresponding alkali fluorides the compounds K2MoFa, RbMoF7, and CsMoF7 form while NaF remains unchanged. With NaF and KF the same behavior towards MoF6 was observed in liquid S02. In IF5, S02, or AsF3 solutions, slightly moist RbF or CsF yield RbMoOF5 and CsMoOF5, respectively, while moist NaF gives an impure residue containing NaMoOF5 and NaF [13], cf. also [14,15]. The reaction of MoF6 with KBr at mole ratio 1: 2 in liquid S02leads to the reduction of MoF6 and formation of potassium hexafluoromolybdate(V) [16]. The reduction of MoF6 by alkali iodides in liquid S02 proceeds in a stepwise manner to produce hexafluoromolybdates(V), -(IV), and -(lll) under appropriate conditions [16]. The use of excess MoF6 results in very rapid formation of MMoF6 (M = Na, K, Rb, or Cs) and liberation of iodine even at - 60°C [17]. With two equivalents of MI (M = Li, Na, Rb, or Cs) per MoF6 an equilibrium between molybdate(V) and -(IV) appears to be established. The precipitation of the molybdate(IV) salt is complete only after a long time but can be accelerated by removal of the iodine. In the case of the potassium salt some hexafluoromolybdate(lll) forms in addition to K2MoF6 [16]. For the formation of Na2MoF6 by reacting excess Nal with MoF6 in liquid S02 see also [18]. No interaction takes place in S02 or methylene chloride solutions between MoF6 and BF3, (n-C4Hg)4NBF4' PF5, AsF5, NbF5, TaF5, MoF5, and (n-C4Hg)4NSbF6 [20]. Mo~ 177 The complex [Agl(pY)4HMoVF6] is oxidized by MoF6 in CH 3CN at 258 K giving [AglII(pY)4(NCCH3)][MoVF6b, py = pyridine [21]. References: [1] Paine, R. T.; Asprey, L. B. (lnorg. Chem. 13 [1974] 1529/31). [2] Anderson, G. M.; Fraser, I. F.; Winfield, J. M. (J. F1uorine Chem. 23 [1983] 403/4). [3] Asprey, L. B.; Paine, R. T., Jr. (U.S. 3'929601 [1974/75]1/3; C.A 84 [1976] No. 124096). [4] Prescott, A.; Sharp, D. W. A.; Winfield, J. M. (J. Chem. Soc. Dalton Trans. 1975936/9). [5] Prescott, A.; Sharp, D. W. A.; Winfield, J. M. (Chem. Commun. 1973 667/8). [6] Anderson, G. M.; Iqbal, J.; Sharp, D. W. A; Winfield, J. M.; Cameron, J. H.; McLeod, A G. (J. Fluorine Chem. 24 [1984] 303/17,306,308,312). [7] Frlec, B. (lnst. Jozef Stefan IJS Rept. R-611 [1972]1/11,6/7; C.A. 79 [1973] No. 26692). [8] Frlec, B.; Selig, H.; Hyman, H. H. (lnorg. Chem. 6 [1967]1775/83). [9] Frlec, B. (Nucl. Inst. Jozef Stefan NIJS Porocilo P-206 [1967] 1/7, 4; C.A 69 [1968] No. 54683). [10] Opalovskii, A A.; Kuznetsova, Z. M.; Khaldoyanidi, K. A. (lzv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1968 No. 2, pp. 29/32; C.A. 69 [1968] No. 80821). [11] Clifford, A. F.; Beachell, H. C.; Jack, W. M. (J. Inorg. Nucl. Chem. 5 [1957/58]57/70, 65). [12] Nikolaev, N. S.; Sukhoverkhov, V. F. (Dokl. Akad. Nauk SSSR 136 [1961] 621/3; Proc. Acad. Sci. USSR Chem. Sect. 136/141 [1961]101/3). [13] Hargreaves, G. B.; Peacock, R. D. (J. Chem. Soc. 1958 4390/3). [14] Beuter, A.; Sawodny, W. (Angew. Chem. 84 [1972]1099/100; Angew. Chem. Intern. Ed. Engl. 11 [1972] 1020/1). [15] Beuter, A; Kuhlmann, W.; Sawodny, W. (J. F1uorine Chem. 6 [1975] 367/78, 368). [16] Edwards, A. J.; Steventon, B. R. (J. Chem. Soc. Dalton Trans. 1977 1860/2). [17] Hargreaves, G. B.; Peacock, R. D. (J. Chem. Soc. 19574212/4). [18] Edwards, A. J.; Peacock, R. D. (Chem. Ind. [London] 1960 1441/2). [19] Barbour, C. J.; Cameron, J. H.; Winfield, J. M. (J. Chem. Soc. Dalton Trans. 19802001/5). [20] Brownstein, S. (Can. J. Chem. 51 [1973] 2530/3). [21] lqbal, J.; Sharp, D. W. A; Winfield, J. M. (J. Chem. Soc. Dalton Trans. 1989 461/4). 2.2.8.8.7 Reactions with Organic Compounds Hydrocarbons. On dissolving MoF6 in n-hexane or cyclohexane at 26°C, absorption bands, not present in either separate component, appear immediately after the solutions are prepared resulting in yellow and orange colorations of the mixtures. The absorption bands are ascribed to intermolecular charge-transfer transitions with the fluoride acting as acceptor [3]. Upon exposure of polyacetylene film to MoF6 vapor, the hexafluoride is intercalated to give a final product of composition MoF6 : (CH)x = 0.11. The intercalation is accompanied by an increase in the electric conductivity of the film by several orders of magnitude.1t is assumed that transition metal hexafluorides, e.g. MoF6, are reduced to stable lower-valent states such as MoFs or MoF~- when incorporated into the host [1, 2]. With benzene and mesitylene at room tempera ture, MoF6 decomposes producing blue precipitates [4]. MoF6 has Iittle effect on Apiezon vacuum grease [12]. Oxygen Containing Compounds. MoF6 is an efficient reagent for the transformation of carbonyl compounds, e.g. aromatic aldehydes and ketones, into gem-difluoro compounds; the MoF6 changes to MoOF4. The reactions take place in CH 2CI2 at room temperature and 12 178 Molybdenum Fluorides atmospheric pressure with BF3 as catalyst. The effect of the BF3 can be explained by the formation of a complex [nBF4J[MoF~~n] which facilitates the attack on the carbonyl group [5]. For a continuation and extension of these reactions see [13]. The photo-initiated reaction of formaldehyde with halides or halogen containing compounds, e.g. MoFs, can be used for laser generation [6]. With anhydrous acetic acid, MoFs reacts with vigorous evolution of heat via MoFs + CH 3COOH ~ MoOF4 + HF + CH3COF. In the presence of KF the compound KMo02F3 forms [7]. The volatile organic products produced by fluorination of some aliphatic carboxylic acids and acid derivatives with excess MoFs at about 130°C are listed in the following table: initial organic volatile organic tin °C time in h mol MoFs per yield compound products mol substrate in % CH 3COOH CH 3CF3 133 17 2.96 63 CH 2(COOHjz CH 2(CF3)2 135 136 4.4 79 CH 2ClCOOH CH 2ClCF3 140 16 2.12 88 CH 2BrCOOH CH 2BrCF3 158 64 2.14 89 CHCl2COOH CHCl2CF3, CHClF2, 140 16 2.58 CHF3, CO 2, CO CF3COOH CF3COF 130 19 2.02 54 CH 3COOCH2CH 3 CH 3CF3 130 16.5 2.20 46 CH 3COOCH3 CH 3CF3, CHF3 134 19 0.89 Usually the carboxyl group is fluorinated but a lack of halogen exchange was observed in substituted acetic acids. Methane derivatives are formed from the reactions with dichloroace tic, difluoroacetic, and glycolic acids, probably caused by decarboxylation of the acid or decarbonylation of the initially formed acid fluoride. The molybdenum-containing product from these reactions is MoOF4 [8]. When difluoroacetic acid is treated in an autoclave with MoFs at 180°C at mole ratio MoFs :acid = 2.4:1, pentafluoroethane forms with 60% yield. Under similar conditions at 190 to 210°C (40 to 45 h) nicotinic, isonicotinic, 2,6-pyridinedicarboxylic, and 4,5-imidazoledicarboxylic acids are fluorinated by excess MoFs to the corresponding trifluoromethyl derivatives of pyridine and imidazole, respectively, in high yields (60 to 80%) [9]. Dichloroacetic acid chloride, CHCl2COCl, reacts with MoFs at 130°C (90 h) to give CHCl2CF3, CHF3, and CO [8]. Substituted benzoyl chlorides, cyclohexane carbonylchloride, and terephthaloyl chloride are fluorinated with moderate yield to the corresponding trifluoro methyl compounds at 130°C [10]; CsHsOC(O)Cl is transformed to CsHsOC(O)F [21]. Nitrogen Containing Compounds. For reactions with N-containing organic acids and acid derivatives see above. With acetonitrile, wh ich is used as a solvent for MoFs, some reaction appears at room temperature after 12 h [11]. MoFs effects the oxidative cleavage of hydrazones in nonpolar organic solvents, such as chlorofluorocarbons (Freons) under mild conditions: Dimethyl- and tosylhydrazones of ke tones and aldehydes (e.g. cyclohexanone, cycloheptanone, benzaldehyde, phenyl acetone, etc.) are cleaved to the carbonyl compounds by treatment with MoFs in Cl2FCCClF2 at O°C. The hydrolysis of the intermediate complexes of the hydrazones with MoFs yields the carbonyl compounds [14]. HaLogen Containing Compounds. For reactions with halogenocarboxylic acids and acid chlorides, see above. Gmelin Handbook Mo SuppL. VoL. B 5 MoFs 179 Carbon difluoride, CF2, reduces MoFs giving CF4 (the composition of the reduced moLybde num fluoride is not given) [17]. In freshLy prepared soLutions of MoFs in perfLuoromethyLcycLohexane, C7F13, a bLue precipi tate sLowly deveLops on the walls of the flask after 2 to 3 d [3]. With perfLuoro aromatic eLectron donors, MoFs produces coLored soLutions indicating charge-transfer interactions; e. g. in hexafluorobenzene or octafluorotoLuene an orange brown coLor appears which persists for as Long as one day. For low MoFs concentrations compLete color Loss occurs on freezing. The charge-transfer absorption bands on dilution confirm that the interactions are of a 1 :1 stoichiometry [4, 18]. With perfluoro-p-xyLene, orange soLutions of Low stabiLity form [4]. MoFs can be handLed in CCL4 as a soLvent for a short time. The absorption spectrum of the soLution indicates a CCL4 donor-MoFs acceptor transition. In the soLution a bLue precipitate forms within 1 d [3]. When MoFs is in excess, sLow haLogen exchange leads to the formation of CCL3F, CCL2F2, CCLF3, and a mixed halide of moLybdenum of composition M02CL3Fs which can be formuLated as Moli'Clg(MoVFsh [15,16]. For the use of haLogeno derivatives of hydrocarbons as soLvents see also p. 182. Sulfur Containing Compounds. A vigorous reaction occurs with CS 2 at room temperature yieLding MoFs, (CF3)2S2, and suLfur. The intermediate formation of CF3S· radicaLs is assumed [15,19]. With (CH30hSO at - 50°C (10 min), MoFs reacts to give CH30S(O)F, CH3F, and MoOF4 [20]. With excess RCsH40C(S)CL (R = H; 0-, m-, or p-CH3; m- or p-F; p-CL; p-Br; m-CF3) at 130 to 190°C compounds RCsH40CF3 form with 40 to 95% yieLd [21]. Compounds Containing Silicon and Other Group IV Elements. Charge-transfer interactions between MoFs and (CH3)4Si or (CH3)4Ge can be deduced from the near UV spectrum of the corresponding soLutions. The observed coLors (yeLLow in diLute and red in concentrated soLutions) disappear when the soLutions are frozen. From soLutions of MoFs in (CH3)4Sn a bLue soLid rapidLy deposits [22,23]. The methyLmethoxosiLanes (CH3hSi(OCH3h, CH3Si(OCH3h, and Si(OCH3)4 react with MoFs at -78 to +20°C to give (CH3hSiF2, CH3SiF3, and SiF4+(CH3)P, respectiveLy. The Mo containing product is MoF(OCH3)s in the first reaction. With the other compounds probabLy MoF2(OCH3)4 is formed [20]. In asolid cocondensate at -196°C Ligand exchange between MoFs and Si(OCH3)4 (moLe ratio 1 :10) Leads to the formation of Mo(OCH3)s (via MoF(OCH3)s) and SiF(OCH3h The pronounced oxidative fluorinating behavior of the MoFs is suppressed by this technique [24]. Trifluoroethoxy trimethylsilane, CF3CH20Si(CH3h, reacts with MoFs in CHFCL2 soLutions to give the trifluoroethoxymoLybdenum fluorides (CF3CH20)nMoFs_n (n =1 to 6) and trimethyLfluorosiLane [25]. MoFs and (C2HshSiF form a Liquid with an intense yeLLow color. In the dark brown CsFs soLution, rapid fluorine exchange between MoFs and (C 2HshSj18F takes pLace at 293 K. Reaction to a smaLL extent can not be excLuded [26]. Phosphorus Containing Compounds. Trisubstituted phosphines, e.g., CsHsPR2 or (CsHshPR (R = C2 10 4 aLkyL), react with MoFs in CH2CL2 at room temperature to yield the difluorophosphoranes CsHsPF2R and (CsHshPF2R, respectiveLy, which were isoLated by distiLLa tion. SimiLarLy, (C4HghPF2 forms from (C4HghP and (CsHshPF3 from (CSHS)2PCI. ProbabLy the reactions proceed in two steps invoLving the formation of a 1:1 or 1:2 compLex between MoFs and the phosphine in the first step foLLowed byan internal redox process within the complex. MoFs reacts aLso with CsHs-PCH=CH2 and [(CH3hNbP, however, difLuorophosphoranes couLd Gmelin Handbook Mo Suppl. Vol. B 5 12" 180 Molybdenurn Fluorides not be isolated [27]. The 1-phenylphosphorinan-4-one 1-oxide is fluorinated by MoF6 in CH 2Cl2 to 1-phenyl-4,4-difluorophosphorinane 1-oxide [28]. Metal-Organic Compounds. MoF6 can be inserted in aluminium polyfluorophthalocyanine (PcAIF)n up to PcAIF(MoF6)o.38' For the reaction the MoF6 is used in the form of its graphite intercalation cornpound C20(MoF6). The C20(MoF6) is therrnally decornposed in an N2 strearn wh ich transports the MoF6 to the (PcAIF)n- The (PcAIF)n is retained at roorn ternperature during the reaction [29]. References: [1] Selig, H.; Holloway, J. H.; Pron, A. (Chern. Cornmun. 1982 729/30). [2] Selig, H.; Holloway, J. H.; Pron, A.; Billaud, D. (J. Phys. Colloq. [Paris] 44 [1983] C3-179/ C3-182). [3] Hammond, P. R. (J. Phys. Chern. 74 [1970] 647/53). [4] Hammond, P. R.; McEwan, W. S. (J. Chern. Soc. A 1971 3812/9). [5] Mathey, F.; Bensoarn, J. (Tetrahedron 27 [1971] 3965/9). [6] Bokun, V. Ch.; Sotnichenko, S. A. (Kinetika Kataliz 23 [1982]311/4; Kinet. Catal. [USSR]23 [1982] 257/60). [7] Nikolaev, N. S.; Kharitonov, Yu. Ya.; Sadikova, A. T.; Rasskazova, T. A.; Kozorezov, A. Z. (Izv. Akad. Nauk SSSR Sero Khirn. 1972 757/64; Bull. Acad. Sci. USSR Div. Chern. Sci. 1972 719/24). [8] Van der Puy, M. (J. Fluorine Chern. 13 [1979] 375/8). [9] Shustov, L. D.; Nikolenko, L. N.; Senchenkova, T. M. (Zh. Obshch. Khirn. 53 [1983]103/5; J. Gen. Chern. [USSR] 53 [1983] 85/6). [10] Mathey, F.; Bensoarn, J. (Cornpt. Rend. C 276 [1973] 1569/72). [11] Prescott, A.; Sharp, D. W. A.; Winfield, J. M. (J. Chern. Soc. Dalton Trans. 1975936/9). [12] Gaunt, J. (Trans. Faraday Soc. 49 [1953] 1122/31, 1123). [13] Mathey, F.; Bensoarn, J. (Tetrahedron 31 [1975] 391/401). [14] Olah, G. A.; Welch, J.; Surya Prakash, G. K.; Ho, Tse-Lok (Synthesis 1976 808/9). [15] O'Donnell, T. A.; Stewart, D. F. (lnorg. Chern. 5 [1966]143417). [16] Stewart, D. F.; O'Donnell, T. A. (Nature 210 [1966]836). [17] Mahler, W. (lnorg. Chern. 2 [1963] 230). [18] Hammond, P. R.; Lake, R. R. (Chern. Cornrnun. 1968987/8). [19] Canterford, J. H.; Colton, R.; O'Donnell, T. A. (Rev. Pure Appl. Chern. 17 [1967]123/32, 127/8). [20] Walker, D. W.; Winfield, J. M. (J. Fluorine Chern. 1 [1971/72] 376/8). [21] Mathey, F.; Bensoarn, J. (Tetrahedron Letters 1973 2253/6). [22] McLean, R. R.; Sharp, D. W. A.; Winfield, J. M. (Chern. Cornmun. 1970452). [23] McLean, R. R.; Sharp, D. W. A.; Winfield, J. M. (J. Chern. Soc. Dalton Trans. 1972676/8). [24] Jacob, E. (Angew. Chern. 94 [1982]14617; Angew. Chern.lntern. Ed. Engl. 21 [1982]142). [25] Handy, L. B. (J. Fluorine Chern. 7 [1976] 641/5). [26] Poole, R. T.; Winfield, J. M. (J. Chern. Soc. Dalton Trans. 1976 1557/60). [27] Mathey, F.; Bensoarn, J. (Cornpt. Rend. C 274 [1972]1095/8). [28] Mathey, F.; Muller, G. (Cornpt. Rend. C 277 [1973] 45/8). [29] Djurado, D.; Fabre, C.; Harnwi, A.; Coussins, J. C. (Mater. Res. Bull. 22 [1987]911/21). Gmelin Handbook Mo Suppl. Vol. B 5 MoFs 181 2.2.8.9 Solubility. SOlutions Inorganic Solvents. SoLubiLities in Liquid krypton have been determined at 118 to 165 K by measuring the integrated absorbance of severaL IR absorption features of MoFs in the saturated soLutions. The data can empiricaLLy be represented by Ln(nr/n14o)=-ßHm/RT, where nr is the number of soLute moLecuLes per cm3 in a saturated soLution at temperature T; at T=140 K, n140=6.8x1018 moLecuLes/cm3; the parameter ßHm=2.87±0.1 kcaVmoL. The enthaLpy of soLution was caLcuLated as 3.023 kcaVmoL (~12.648 kJ/moL) [1]. In Liquid anhydrous HF the soLubility is 1.5 moL MoFs (314.925 g) in 1000 9 HF (23.95 wt%) at room temperature [2], 14.28 wt% at O°C [3], and 18.5 ± 1 wt% at - 5°C [4, 5]. SoLutions of MoFs in the anhydrous soLvent are nonionic in character as was demonstrated by eLectric conductiv ity measurements [4,5]. The Liquid-solid phase equiLibria in the MoFs-HF system, determined by differentiaL thermography, are plotted in Fig. 47. The system shows a restricted miscibiLity of the compounds with the upper temperature Limit of insoLubiLity at 120 ± 2°C. The composition of the eutectic point couLd not be determined accurateLy owing to the Low concentration of the MoFs in it. The temperature of the eutectic coincides with the melting point of HF. Liquid-vapor equiLibria were investigated by a static method at 2280 and 1520 Torr. The system exhibits positive deviation from Raoults' Law and forms an azeotrope the composition of which changes insignificantLy with the temperature. In the temperature range 32 to 68°C the temperature dependence of the pressure and composition of the azeotrope can be described by Log p=7.522-1300/T (p in Torr, T in K) and N=0.932-0.0017·t (N is the concentration of HF in the azeotrope in moLe fractions; t in 0c) [6]. The meLting curve for the binary system was determined for 0 to 5.0 moL% HF. The depression of the meLting point ß T of MoFs is 0.1 K at 0.12 moL% HF and 1.5 K at 4.79 moL% HF (seLected vaLues). A general equation for ß T was deduced and appLication to a method for determination of HF in MoFs was proposed [7]. 150 liquid solution 120'[ 100 ~ 50 .S 175'[ ~ -cr-- ::::> 0 0 ~ soluti on + I -8.9'[ 0 t=: Fig. 47. Liquid-solid equiLibria of the HF-MoFs '"c. system; (I) high-temperature modification of E ~ solution + II MoFs, (11) Low-temperature modification of MoFs, -50 (111) HF [6]. -1 OO'-::--~--"L,---::"-:.:...c=--::'-,---,' MoF5 HF The eLectricaL conductivity of a saturated MoFs soLution in HF at O°C is 0= 13.01 X 10-5 g-l. cm-1, corrected for the conductivity of the soLvent HF: 0corr= 8.45 X 10-5 g-l. cm-1. The degree of eLectrolytic dissociation is a = 0.03%. The MoFs Raman shifts of a 1.50 M HF soLution are V1 = 744, V2 = 651, and V5 = 320 cm-1 [2]. The soLubiLity in CLF3 at O°C is 95.1 ±0.5 wt% MoFs [8]. The Liquid-vapor equiLibria of mixtures of MoFs and CLF3 were studied at temperatures in the range 40 to 88°C, at a constant pressure of 2600 Torr. The dew and boiLing curves indicate the existence of an azeotrope with minimum boiling point at 44.2°C for a concentration of 88.2 moL% CLF3 [9. 10]. GmeLin Handbook Mo SuppL. VoL. B 5 182 MoLybdenum Fluorides On dissoLving MoF6 in BrF3 an enthaLpyof soLution of 3.03 ± 0.10 kJ/moL MoF6 was caLorime tricaLLy measured [11]. Organic Solvents. CH 2CL2, CHFCL2, and chLorofLuorocarbons have been used as soLvents in fLuorination of organic compounds by MoF6• CH 3CN, CCL4, and C7F13 were found to be suitabLe soLvents for MoF6 for short handling periods but exhibit changes after one or severaL days, see p. 177ft. A soLution of MoF6 in C6F6 is dark red [15]. The enthaLpy of soLution of MoF6 in n-hexadecane was determined gaschromatographicaLLy as ö.H = - 5.5 kcaLlmol. For KeL-F-10 (poLy{chLorotrifLuoroethyLene», the same vaLue resuLts, and for the sorption of MoF6 on carbon bLack - 5.4 kcaLlmoL were found.Together with the reLative retention voLumes measured, the eLectrostatic interaction energy = - 5.2 kcaLlmoL resuLts (same vaLue for the three substances) [16]. DichLorotetrafLuoroethane, C2CL2F4, and MoF6 show compLete miscibiLity. The soLutions deviate LittLe from the ideaL soLution Law, with activity coefticients being very cLose to unity [12]. In the tetrachLoroethyLene-MoF6 system the temperature dependence of the totaL pressure at 0 to 90°C and the Liquid-vapor equiLibria at 20°C have been investigated. The system shows positive deviation from RaouLts' Law without formation of an azeotrope [13]. MoF6 is almost infiniteLy miscibLe with hexachLoro-1 ,3-butadiene (HCBD) in the temperature range 5 to 30°C. The enthaLpies of soLution for gaseous and soLid MoF6 in HCBD are - 4725.2 and + 971.3 caLlmoL, respectiveLy [14]. References: [1] Beattie, W. H.; Maier, W. B., 11; Freund, S. M.; HoLLand, R. F. (J. Phys. Chem. 86 [1982]4351/6). [2] FrLec, B.; Hyman, H. H. (Inorg. Chem. 6 [1967]1596/8). [3] NikoLaev, N. S.; OpaLovskii, A. A. (Zh. Neorgan. Khim. 4 [1959]1174/83; Russ. J. Inorg. Chem. 4 [1959] 532/6). [4] NikoLaev, N. S.; VLasov, S. V.; BusLaev, Yu. A.; OpaLovskii, A. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1960 No. 10, pp. 47/56, 51; C.A. 1961 12014). [5] NikoLaev, N. S.; VLasov, S. V.; BusLaev, YU. A.; OpaLovskii, A. A. (Fiz. Khim. AnaLiz. Tr. YubiLeinoi Konf., Novosibirsk 1960 [1963], pp. 97/103, 100; C.A. 62 [1965] 4673). [6] Prusakov, V. N.; Korobtsev, V. P.; Markov, S. S.; Ezhov, V. K.; KhokhLov, V. A.; Bosenko, I. I. (Zh. Neorgan. Khim. 17 [1972] 2549/52; Russ. J. Inorg. Chem. 17 [1972]1334/6). [7] Hedge, W. D. (K-1698 [1968]1/22; C.A. 69 [1968] No. 70415). [8] NikoLaev, N. S.; Sukhoverkhov, V. F. (Dokl. Akad. Nauk SSSR 136 [1961] 621/3; Proc. Acad. Sci. USSR Chem. Sect. 136/141 [1961]101/3). [9] CarLes, M. J.; Aubert, J. (J. Chim. Phys. Physicochim. BioL. 67 [1970] 671/5). [10] CarLes, M. J.; Reynes, J. A.; BethueL, L.; Aubert, J. (CEA-CONF-2171 [1972]1/8,5/6; C.A. 79 [1973] No. 140116). [11] Richards, G. W.; WooLf, A. A. (J. FLuorine Chem. 1 [1971/72] 129/39, 133). [12] Reynes, J. A.; Carles, M. J.; Aubert, J. (J. Chim. Phys. Physicochim. BioL. 67 [1970]676/9). [13] GaLkin, N. P.; Bogdanov, G. V.; Fedorov, V. D.; Orekhov, V. T. (Zh. Neorgan. Khim. 16 [1971]496/9; Russ. J. Inorg. Chem. 16 [1971] 262/4). [14] GaLkin, N. P.; Bertina, L. E.; Orekhov, V. T.; PakLenkov, E. A. (Zh. Fiz. Khim. 49 [1975]2454; Russ. J. Phys. Chem. 49 [1975] 1443). [15] PooLe, R. T.; WinfieLd, J. M. (J. Chem. Soc. DaLton Trans. 1976 1557/60). [16] Isakov, V. P. (Zh. Fiz. Khim. 47 [1973] 702/4; Russ. J. Phys. Chem. 47 [1973] 395/6). Gmelin Handbook Mo SuppL. VoL. B 5 MoLybdenum FLuoride Ions 183 2.2.9 Molybdenum Fluoride Ions 2.2.9.1 MOmF~+ Cations MoF~ ions with n =1 to 5 occur in the mass spectrum of MoF6 and MoFs at room temperature at 70 eV eLectron impact (see pp. 99 and 142, respectiveLy) and in that of the saturated vapor over MoF3 at 964 K (see p. 76) [1]. OnLy MoF+, MoF!, and MoF:j were detected in the mass spectrum of MoF4 [2,3], MoOF4 [2,4], and in that of the vapor of the MoF3-Mo oxide fluoride system at 751 K [5]. However, MoFt has aLso been found in other investigations in the mass spectrum of MoF4 (see p. 88) [1]. The MoFt and MoFt ions observed in the mass spectrum of MoFs vapor are said to be formed mainLy from trimers and, to a Lesser extent, from tetramers [8]. The highest intensity is aLways observed for the (parent-Less-one fLuoride)+ ion [3]. Forthe occurrence of MoF~+ ions with n =1 to 4 in the mass spectrum of MoF6 see p. 165. SmaLL amounts of the dimeric ions M02Ft, M02Ft, and M02Ft were detected in the mass spectrum of the saturated vapor over MoF3 at 964 K. Their intensities at different ionization voLtages indicate that M02F6 and M02F10 are the moLecuLar precursors [1]. For M02Ft mainLy the trimer and to a Lesser extent the tetramer of MoFs are said to be the moLecuLar precursors [8]. The dimeric and trimeric species M02F~ (n=8 to 10) and M03F~ (n=13 to 15) form at 60eV eLectron impact in the vapor over MoFs at 296.4 K, the main component being M02Ft. Tetrameric ions, M04F~ (n =18 to 20), occur onLy in traces. The appearance potentiaLs of the M03Fis and M03F~ ions give evidence that these ions are formed from the corresponding moLecuLes. The other M02F~ and M03F~ species have trimeric and tetrameric moLecuLar precursors ~nd the M04F~ species have tetrameric and pentameric precursors, see [8] and p.99. The foLLowing tabLe Lists the appearance potentiaLs in eV for MOmF~ ions produced by different methods: MOmF~ MoF6 MoF6 +Mo, pure MoFs from sat. vapor MoF3+ at18°C SF6 + Mo at MoFs MoF6 +Mo over MoF3 Mo02F2 1000 to 2000 K a) at 80°C at 500°C at 691°C at 478°C [6] [9,10] [6] [6] [1] [5] MoF+ 35.5 8.0±0.3 36 >25.0 MoF! 29.5 9.00±0.15 b) 31 14.3±1.0c) 22.0 ± 1.0 14.0±0.3c) 19.0±1.0d) MoF:j 23.5 9.88±0.10 23 10.2±0.5c) 12.5±0.5 14.01 ±0.5d) 14.5 ± 0.5 MoFt 19.5 10.11 ±0.10 18 16.5 9.74±0.2 MoFt 16 10.60±0.1Oe) 19 10.81 ±0.2 15.2±0.3g) 15.2±0.2f) M02Ft 15.5 15.0 _ b) a) Lowest threshoLds. MoLecuLar precursor MoF2. - c) MoLecuLar precursor MoF3. - d) MoLecuLar precursor MoF4. - e) MoLecuLar precursor MoFs. - f) MoLecuLar precursor MoF6• - g) From [7]; MoF6 at room temperature. In the ionization efficiency curves the Less abundant MoFt has a strong onset at 19 eV and a weaker one near 15 eV attributed to fragmentation of MoF6 and MoOF4, respectiveLy [9]. The appearance potentiaL 11.4 ± 0.2 eV for M03Fis and 11.6 ± 0.2 eV for M04F~ was determined for the appearance of these ions in the vapor over MoFs (crystaLLine or supercooLed Liquid) at 296.4 K [8]. Gmelin Handbook Mo Suppl. Vol. B 5 184 MoLybdenum Fluoride Ions M06Ft. For this hypotheticaL cLuster ion, the energy LeveLs and the charge distribution have been calcuLated by an SCF-SW-Xa calculation [11] (seLf consistent field-scattered wave calcuLation with statistical treatment of the exchange field). This method is reviewed in [12]. aLso see [13] for a review of the Xa method. The M06F3+ cluster ion is expected to be diamagnetic, the highest occupied orbital being an e9 LeveL occupied by four eLectrons. There will be an important ionic contribution to the Mo-F bonds. In the se ries M06Xt (X = F, CI, Br, 1), the popuLation is decreased with the X = F case for those levels wh ich would contribute to the Mod-Mod bonds. This might explain why the M06F3+ cLuster so far has not been prepared despite the fact that it is caLculated as the most stable cluster in the X = F, CI, Br, and I se ries. The energy of this cluster ion is compared with the adsorption energy of fLuorine on moLybdenu m [11]. References: [1] ALikhanyan, A. S.; Steblevskii, A. V.; Malkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978]1477/82; Russ. J. Inorg. Chem. 23 [1978] 814/7). [2] StrehLow, R. A.; Redman, J. D. (ORNL-4254 [1968]134/6; N.S.A. 22 [1968] No.47112). [3] Redman, J. D.; Strehlow, R. A. (ORNL-4229 [1968] 37/9; N.S.A. 22 [1968] No. 25374). [4] Paine, R. T.; McDowell, R. S. (Inorg. Chem. 13 [1974] 2366/70). [5] ALikhanyan, A. S.; Steblevskii, A. V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978] 2549/52; Russ. J. Inorg. Chem. 23 [1978]1412/3). [6] Weaver, C. F.; Redman, J. D. (ORNL-4449 [1970]116/21, 117). [7] Kleinschmidt, P. D.; Lau, K. H.; HiLdenbrand, D. L. (J. Chem. Thermodyn. 11 [1979]765/72, 767). [8] Gotkis, I. S.; Gusarov, A. V.; Pervov, V. S.; Butskii, V. D. (Koord. Khim. 4 [1978] 720/4; Soviet J. Coord. Chem. 4 [1978] 536/40). [9] Hildenbrand, D. L. (J. Chem. Phys. 65 [1976] 614/8). [10] Hildenbrand, D. L. (Nucl. Instrum. Methods Phys. Res. 186 [1981] 357/63). [11] Seifert, G.; Grossmann, G.; Müller, H. (J. Mol. Struct. 64 [1980]93/102). [12] Johnson, K. K. (Advan. Quantum Chem. 7 [1973]143/85). [13] Slater, J. C. (Advan. Quantum Chem. 6 [1972]1/92). 2.2.9.2 MoF~l 10 3)~ Anions, n = 4 to 8 Gaseous MoF;j", MoFs, and MoFs.ln the vapor phase the ions MoF;j", MoF5, and MoF6" form by direct electron attachment to MoF6, see p. 165, and by collisionaL ionization of MoF6 with alkali metals (Na, K, Cs) in crossed beams at thermaL or eV-range energies, see p. 168. The dissociation energies D298(F4Mo-F-) = 382.0 ± 20.1 and 380.3 kJ/mol are deterrnined from the gas-phase equilibrium MoF4+ 2 BeF3";;::::':: MoF5 + Be2F5 and from reactions invoLving AIF4" ions, respectively. From the former equiLibrium thermodynamic functions have been derived. Sr and (Gr - H~8)1T have been caLcuLated for T = 100 to 1200 K at 100 K intervaLs. For gaseous MoF5, S~8=352.7 J·moL~l·K~l [1]. A bond dissociation enthaLpy D(F5Mo-F~)=418.2kJ/moL C~4.34eV) was obtained frorn mass spectrometric measurements of equiLibrium constants of severaL ion-rnoLecuLe reactions. D(F5Mo-F~) = 426.3 kJ/moL (~4.42 eV) folio ws from equiLibrium measurements [2]. öHf'.298.2[MoF6"(g)]=-2068±6kJ/mol has been determined by hydrolysis caLorimetry on MMoF6 (M = K, Rb, Cs) [3]. Thermodynamic functions have been derived for the MoF6"(g) ion Gmelin Handbook Mo SuppL. VoL. B 5 185 from the study of the gas-phase equilibrium MoFs + 2BeF3~MoFij + Be2Fs.Sr and (Gr -H29a)fT have been calculated for T=100 to 1200 K at 100 K intervals. S~a[MoFij(g)]=374.8 J. mol-1. K-1 [1]. Crystalline compounds containing complex f1uoromolybdate anions are known with molyb denum in the oxidation states 3 through 6. MOIIIF~-o Hexafluoromolybdates(lII) of composition M2M'MoFs (M = K, Rb, Cs, TI; M'= Na, K, TI) can be obtained by reacting MoF3 with fluorides MF and M'F in stoichiometric proportions at 500 to 600°C, see p. 84. Also the reduction of MoFs by KI in liquid S021eads to hexafluoromo lybdates(lII) as the final product, see p. 176. MONF~-. From the reaction of MoFs with Nal or KI in liquid S02 the hexafluoromolybdates(IV) Na2MoFs and K2MoFs have been isolated, see p. 176. The hydrazinium hexafluoromolybda te(IV) can be produced by reducing MoFs with excess N2HsF2 in CH 3CN, see p. 176. For the 3T19 electronic ground state of MoF~- a QRMP calculation (see the section on MoFij, below) assuming 0h symmetry for the MoF~- ion yields total energies and orbital energies 10; for different Mo-F distances of 1.65 A~r~2.3 A. For 3t2g , 10;=-5.2 eV at the calculated equilibri um distance re = 2.01 0 A. Mulliken gross and overlap populations were calculated. Atomic charges at Mo and F were calculated as + 1.81 and - 0.63 [4]. Taking electron correlation into account (by configuration-interaction calculations) re = 2.025 A results (for the total energy see the paper) [5]. MON~-o Crystalline fluorides LnMoF7 result from solid state reactions between MoF4 and LnF3 with Ln = Y and all lanthanides except Dy, see p. 92. MovFijo The complex hexafluoromolybdate(V) anion, MoFij, has been isolated with a variety of cations. The preparation methods used are the reactions of MoFs with fluorides MF (M = K, Rb, Cs) at high temperatures (see p. 114), the reaction of MoFs with alkali iodides MI (M = Na, K, Rb, Cs) or KBr in liquid S02 (see p. 176), and the reaction of MoFs with metals (Zn, Cd, Hg, TI, Co, Cu) or N2HsF2 in CH3CN (see p. 176). The reactions of MoFs with NO, NOCI, or NH4F also yield hexafluoromolybdates(V), see p. 171. The theoretical studies [1,2] of the MoFij ion have been based on the assumption of 0h symmetry for the ion [6,7]. Expected distortions of the octahedron to lower symmetry (e.g., D4h , see [8]) will have only minor effects on the energy levels of the d1 system [7], also see [6]. The labelling of the occupied levels of the electronic ground state, ... (4eg)4 (2t29 )S (7a1g)2 (6t1u )S (1t2u )S (1t19 )S (7t1u)S (3t29 )1, 2T29 used below follows the usage in [6], however, with the sequence ... (1 t19 )S (7t1u)s ... interchanged with respect to the paper [6]. For this ground state, a Hartree-Fock-Roothaan calculation was performed using a quasi-relativistic model-potential (QRMP) method [7] (for the relativistic corrections, see [9], for the model potential, see [10, 11]). Total energies and orbital energies f i were calculated for Mo-F distances 1.6q A~ r~2.3 A. The f;(r) curves were in the above ordering at the equilibrium distance re and showed 4eg and 2t29 to be bonding, 7a19 through 7t1u to be of predominantly ligand character, and 3t2g to be antibonding. For the latter, f;(re) =-1.5 eV [7]. The Xa-discrete variational method described in [12] was used in [6] in aversion that took spin polarization into account. The calculations were restricted to a fixed distance, r =1.85 A. They yielded the same bonding characteristics, but for 3t2g , 10; = -3.2 eV. The a- and ß-spin orbital energies of the other levels Iisted above are also given in [6] and differ significantly from the values indicated graphically in [7]. Mulliken gross and overlap populations were calculated [6,7]. Atomic charges at Mo and F were given as+1.91 and -0.49 [7] or+0.92 and -0.32 [6]. Absorption spectra extending from 10000 to 35000 cm-1 of crystalline CsMoFs showed a transition at 24000 cm-1 attributed to 2Eg+-- 2T2g . Two further peaks, at 29000 and 35000 cm-1, Gmelin Handbook Mo Suppl. Vol. B 5 186 MoLybdenum Fluoride Ions are possibLy due to charge-transfer transitions or spin-orbit splittings of 2"f 2g and 2Eg states [13] (see aLso "MoLybdenum" Suppl. Vol. A 2a, 1985, p.71). A positive eLectron affinity foLLowed from the QRMP caLcuLation described above. Adiabatic and verticaL vaLues were A =1.76 and 1.05 eV [7]. Configuration-interaction caLcuLations (to take eLectron correLation into account) Lowered the adiabatic vaLue to 0.58 eV [5]. EquiLibrium (free ion) Mo-F distances re =1.909 A [7] and 1.936 A [5] were theoreticaLLy caLcuLated. Wavenumbers (in cm-1) of five (active) fundamentaL vibrations Vi (i =1 to 5) were taken from Raman (V1' V2' vs) and IR (V3' V4) spectra of severaL solid saLts containing the MoFil ion. These spectra were anaLyzed assuming the same seLection ruLes as for the neutraL MoF6 moLecuLe (see p. 122): saLt V1 remark Ref. a) CsMoF6 685 598 635 250 274 [15] NOMoF6 688 450 236 [16] NOMoF6 615 [17] a) From KMoF6{s): V1 =687, V3 = 639, V4 = 249. Raman excitation was by the 488 nm Line of an Ar+ Laser [15]. OLder vaLues: V1 = 676 (solid CsMoF6 and soLutions of AgMoF6 and CsMoF6 in CH3CN) [18], v3=623 (solid aLkaLi saLts) [19]. 001 = 642 cm-1 was theoreticaLLy caLcuLated [5]. VaLence force constants (in mdyn/A; for definition, see p. 138) were derived from the three stretching vibrations (V1 to v3) reported in the first row of the tabLe above: f, = 3.78, f" = 0.21, f".=0.64 [15]. MOVIFi· MoLybdenum{VI) forms fLuoromoLybdates of composition MIMoF7 and M~MoFa. Compounds MMoF7 (M = NO, N02, NH4, K, Rb, Cs) can be prepared by reacting MoF6 with the corresponding fluorides directLy or with IFs or CLF3 as soLvents, see pp. 172 and 176. The vibrationaL spectra of MoFi ions have been recorded for 200 cm-1 ~v~1050 cm-1 (IR) and 10 cm-1~v~1000 cm-1 (Raman) on MMoF7 (M = K, Rb, Cs). The MoFi ion is pentagonaL bipyramidal (Dsh) in CsMoF7• The foLLowing vibrationaL frequencies (in cm-1) have been recorded [20]: IR ...... 330{w) 356{m) 500{w) 635 (vs) Raman ...... 321 (w) 433{w) 687 (vs) assignment .. v10{e2) v4{a2) va(e'!) [impurity?] v3{a2), vs{e;) v1(a;) The MoFi ion in MMoF7 (M = K, Rb) has a reduced symmetry since at Leasttwo (up to 4) of the 5 Raman bands observed coincide with IR active modes (of which a totaL of 10 was found), see the paper [20]. A broad, very strong IR absorption band is observed at 640 cm-1 with soLids containing the MoFi ion [14] (at 645 cm-1 with KMoF7 [19]); it occurs at 627 cm-1 with N02MoF7 [14]. MovlFr. FLuoromolybdates M2MoFa with M = Li, Na, K, Rb, Cs have been prepared from MoF6 and excess alkali fluoride, see p. 172. The vibrationaL spectra of MoFr ions have been recorded for 200 cm-1~v~1050 cm-1 (IR) and 10 cm-1~v~1000 cm-1 {Ra man) on M2MoFa (M = K, Rb). The internaL modes observed are consistent with square antiprismatic MoF~- ions (D4d). The very weak IR bands at 635 (K) and 628 cm-1 (Rb) cLose to the very strong Raman bands at 639 (K) and 636 cm-1 (Rb) indicate a Gmelin Handbook Mo Suppl. Vol. B 5 MoF~' 103)- 187 sLight distortion frorn D4d syrnrnetry. No assignrnents are given for the rnodes observed and listed below [20]: IR bands in ern-1 Rarnan shifts in ern-1 K2MoFB .•.. 355(s) 390(w) 583 (vs) 635(vw) K2MoFB •••• 401 (rn) 639 (vs) Rb 2MoFB ••• 354(rn) 388(vw) 576(vs) 628(vw) Rb 2MoFa ... 396(w) 636(vs) References: [1] Sidorov, L. N.; Borshehevsky [Borshehevskii], A Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chern. Phys. 71 [1982] 145/56). [2] Borshehevskii, A Ya.; Sidorov, L. N.; BoltaLina, O. V. (Dokl. Akad. Nauk SSSR 285 [1985] 377/81; Dokl. Phys. Chern. Proe. Aead. Sei. USSR 280/285 1109/12). [3] Burgess,J.; Haigh, 1.; Peaeoek, R. D.;Taylor, P. (J. Chern. Soe. Dalton Trans. 19741064/6). [4] Sakai, Y.; Miyoshi, E. (J. Chern. Phys. 87 [1987] 2885/92). [5] Miyoshi, E.; Sakai, Y.; Murakarni, A.; Iwaki, H.; Terashirna, H.; Shoda, T.; Kawaguehi, T. (J. Chern. Phys. 89 [1988] 4193/8). [6] Gutsev, G. L.; BoLdyrev, A. I. (Mol. Phys. 53 [1984] 23/31). [7] Sakai, Y.; Miyoshi, E. (J. Chern. Phys. 87 [1987] 2885/92). [8] GiLLespie, R. J. (J. Chern. Edue. 47 [1970] 18/23). [9] Cowan, R. D.; Griffin, D. C. (J. Opt. Soe. Arn. 66 [1976]1010/4). [10] Bonifaeie, V.; Huzinaga, S. (J. Chern. Phys. 60 [1974] 2779/86). [11] Huzinaga, S.; KLobukowski, M.; Sakai, Y. (J. Phys. Chern. 88 [1984]4880/6). [12] Gutsev, G. L.; Levin, A. A (Chern. Phys. 51 [1980] 459/71). [13] Brown, D. H.; RusseLL, D. R.; Sharp, D. W. A (J. Chern. Soe. A 1966 18/20). [14] Geiehrnan, J. R.; Srnith, E. A; OgLe, P. R. (Inorg. Chern. 2 [1963]1012/5). [15] Beuter, A.; Sawodny, W. (Z. Anorg. ALLgern. Chern. 427 [1976] 37/44). [16] Sharnir, J.; Malrn, J. G. (Inorg. Nuel. Chern. H. H. Hyrnan Mern. Vol. 1976, pp. 107/11). [17] Geiehrnan, J. R.; Srnith, E. A.; Trond, S. S.; OgLe, P. R. (Inorg. Chern. 1 [1962] 661/5). [18] Preseott, A.; Sharp, D. W. A.; WinfieLd, J. M. (Chern. Cornrnun. 1973667/8). [19] Peaeoek, R. D.; Sharp, D. W. A. (J. Chern. Soe. 19592762/7). [20] Beuter, A.; KuhLrnann, W.; Sawodny, W. (J. Fluorine Chern. 6 [1975] 367/78). Gmelin Handbook Mo Suppl. Vol. B 5 188 Mo-F-Xe Compounds 2.3 Compounds of MoLybdenum with FLuorine and Xenon Studies of the MoFs-XeF2 system by DTA led to the phase diagram given in Fig. 48.lt shows the formation of the compound XeF2 • MoFs congruently melting at 124 ±1 °C and that of an incongruently melting compound with the approximate composition XeF2 ·4MoF6 [1]. 140 120 100 ;-' 80 ~ 60 .2 ~ 40 CL ~ 20x~--- ..... x-xx.x-x~x.. ;:<.xx_x-x_ Fig.48. Phase diagram of the MoF6-XeF2 system [1]. MoF, 02 0.4 0.6 08 XeFz mole traction XeFz XeF2 'MoFs is a white crystalline substance wh ich is very reactive towards organic com pounds [1]. The IR spectrum of the compound is plotted in paper [2] for the approximate wave number range of 400 to 750 cm-1. The structure is assumed to be ionic, XeF+· MoFi, with pentagonal bipyramidal (DSh) MoFi. The following IR frequencies and assignments have been given [2]: V in cm-1 ••••••• 683 (m) 657 (s) 570 (w, br) 507 (s) 450 (w, br) 413 (sh) tentative assignment ...... Mo-F Mo-F Xe--F Mo-F or Mo-F-Mo Xe--F-Mo Mo-F-Mo(?) (?) The Raman spectrum between 118 and 739 cm-1 at room temperature shows only bands corresponding to the binary fluorides. At liquid nitrogen temperature, bands of solid XeF2 and of gaseous MoF6 were found indicating that XeF2 • MoF6 is an adduct with weak bonds. Frequencies corresponding to XeF+ could not be observed [3]. References: [1] Legasov, V. A.; Marinin, A. S. (Zh. Fiz. Khim. 46 [1972] 2649/51; Russ. J. Phys. Chem. 46 [1972] 1515/6). [2] Klimov, V. D.; Marinin, A. S. (Deposited Doc. VINITI-598-74 [1974]1/18; Zh. Prikl. Spektrosk. 21 [1974]184; J. Appl. Spectrosc. [USSR] 21 [1974] 989). [3] Ezhov, V. K.; Koroshev, S. S. (Zh. Fiz. Khim. 52 [1978]1339/40; Russ. J. Phys. Chern. 52 [1978] 772/3). Gmelin Handbook Mo Suppt. VoL B 5 Mo.lybdenum Oxide Fluo.rides 189 2.4 Compounds 01 Molybdenum with Fluorine and Oxygen 2.4.1 Molybdenum Oxide Fluorides Survey. This sectio.n co.ntains the anhydro.us o.xide fluo.rides and tho.se co.ntaining water and/o.r OH gro.ups. Fo.r the hydro.us co.mpo.unds vario.us fo.rmulas can be fo.und in the literature because the structures are no.t kno.wn in mo.st cases. The o.xide fluo.rides o.f mo.lybdenum (and tungsten) in o.xidatio.n state + 6 are the mo.st studied transitio.n metal o.xide fluo.rides and there is detailed kno.wledge o.f the preparative metho.ds and pro.perties o.f Mo.OF4 and Mo.02F2. Only a little wo.rk has been do.ne o.n the lo.wer mo.lybdenum o.xide fluo.rides. The existence o.f Mo.OF2 and Mo.OF3 was repo.rted fo.r the first time in 1965 and 1968, respectively. An anhydro.us o.xide fluo.ride o.f Mo. II1 co.uld no.t be detected. In additio.n to. the well-defined o.xide fluo.rides the existence o.f Mo.03_ xFx co.mpo.unds with x< 1 has been repo.rted. These blue- and go.lden-co.lo.red pro.ducts sho.w so.me resemblances to. the hydro.gen insertio.n co.mpo.unds o.f Mo.03, HxMo.03, also. deno.ted as "bronzes" , see "Mo.lybdenum" Suppl. Vo.l. B 3a, 1987, p.6. All the o.xide fluo.rides are so.lids. They have been handled in Kel-F (po.ly(chlo.ro.trifluo.ro. ethylene)) [1 to. 4], FEP-Teflo.n, Mo.nel [2], Ni [4,5], o.r pyrex equipment [4]. Mo.OF4 has to. be sto.red in an argo.n atmo.sphere [3] o.r in a dry bo.x [4]. References: [1] Paine, R. T.; McDo.well, R. S. (lno.rg. Chem. 13 [1974] 2366/70). [2] Bo.ugo.n, R.; Bui Huy, T.; Charpin, P. (lno.rg. Chem. 14 [1975]1822/30, 1822). [3] Burns, R. C.; O'Do.nnell, T. A.; Waugh. A. B. (J. Fluo.rine Chem. 12 [1978] 505/17, 507). [4] Ho.llo.way, J. H.; Schro.bilgen, G. J. (lno.rg. Chem. 19 [1980] 2632/40, 2639). [5] Atherto.n, M. J.; Burgess, J.; Ho.llo.way, J. H.; Mo.rto.n, N. (J. Fluo.rine Chem.11. [1978]215/24, 217). 2.4.1.1 MoOF·3H20 Older data are given in "Mo.lybdän " , 1935, p. 151. The so.lid co.mpo.und co.uld no.t be o.btained with the perfect sto.ichio.metry Mo.OF·3 H20. Sampies precipitated fro.m aqueo.us so.lutio.ns o.f the co.rrespo.nding chlorine co.mpo.und by adding NH4 F so.lutio.ns at freezing temperature o.r 25°C had co.mpo.sitio.ns co.rrespo.nding to. [Mo.OFo.96(OH)o.04(H 20hHH20)O.28 and [Mo.OFo.91 (OH)O.09(H20hHH20)o 18' respectively. It was sho.wn that the water in excess o.f a hydratio.n number o.f three was o.nly lo.o.sely held and it was co.ncluded that the o.nly hydrate o.f Mo.OF existing under no.rmal co.nditio.ns is Mo.OF·3 H20 and no.t the previo.usly repo.rted tetrahydrate (see "Mo.lybdän" , 1935, p. 151) [1]. X-ray and electron diffractio.n data indicate that the co.mpo.und is iso.mo.rpho.us with the o.rtho.rho.mbic chlorine analo.gue. The unit cell parameters are a=7.10, b=8.28, c=18.24 A; Z=12 [1]. The vibratio.nal and electronic spectra and magnetic susceptibility determinatio.ns lead to. the co.nclusio.n that the co.mpo.und is pro.bably an o.xygen-bridged chain po.lymer, [Mo.OF(H20h]n, rather than a species co.ntaining MO--0 o.r Mo-O-H gro.ups [2]. The magnetic susceptibility at ro.o.m temperature is Xmol< 20 X 10-10 S.1. units rather than the -800 x10-10 S.1. units expected fo.r mo.no.meric Mo.HI species [2]. Bands in the IR spectrum (reco.rded fro.m 200 to. -4000 cm-1) at 472 and 682 cm-1 are attributed to. Mo-O-Mo. bridges and indicateeither a be nt o.xygen bridge o.f a dimeric mo.lecule Gmelin Handbook Mo Suppl. Vol. B 5 190 MoLybdenum Oxide FLuorides or bends (at either Mo or 0) of an oLigomeric or poLymerie moleeule. Frequencies found are 3410, 3150, 3035, 2817, 1614, 754, 682, 472, 310, and 282 cm-1. The band at 754 cm-1 is attributed to a (presumabLy terminaL) Mo-F bond. Diffuse refLectance spectra between -3900 and 50000 cm-1 yieLded features at 44000, 37300, 30600, 26200, 22200,19000,15500,9520, 7000,5560,5180, and 4920 cm-1 [2). References: [1) Stabb, D. J. (AustraLian J. Chem. 29 [1976) 711/5). [2) Stabb, D. J. (AustraLian J. Chem. 29 [1976) 717/21). 2.4.1.2 MoOF2 Thermogravimetry shows that the hydrate MoOF2 • H20 (see beLow) Loses the water upon heating in a vacuum and does not change composition up to 600°C [1). The reaction of MoOCL2 with HF yieLds MoOF2 with a cubic structure (Re03 type) with a = 3.896 ± 0.003 A [2). The enthaLpy of formation, the entropy, and the heat capacity have been estimated for the gaseous species as öHt. 298 = -1709 kJ/moL, S298 = 301 J. moL-1. K-1, and Cp. 298 = 63 J. moL- 1 • K-1• The corresponding data for solid MoOF2 are -1936, 112, and 93, respectiveLy. Estimated enthaLpy and entropy of sublimation are ÖH S • 298 = 227 kJ/moL and ÖSS • 298 = 206 J. moL-1. K-l, respectiveLy [3). The magnetic susceptibiLity was studied by the Faraday method. The temperature dependence of the effective magnetic moment !leff is as foLLows [4): !leff in!lB ...... 0.82 0.92 0.95 1.06 1.191.271.331.371.401.46 Tin K ...... 78 100 111 138 181 212 233 251 263 291 These strongLy reduced effective magnetic moments seem to be due to antiferromagnetic coupLing and suggest a poLymerie structure invoLving Mo-F-Mo bridges [4). References: [1) Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981)573/6; Russ. J. (norg. Chem. 26 [1981) 310/2). [2) Schäfer, H.; Schnering, H. G.; Niehues, K.-J.; Nieder-VahrenhoLz, H. G. (J. Less-Common Metals 9 [1965) 95/104, 100). [3) Dittmer, G.; Niemann, U. (Mater. Res. BuLL. 18 [1983) 355/69, 364/7). [4) ELLert, O. G.; Butskii, V. D.; Novotortsev, V. M.; Pervov, V. S.; VoLkov, V. V.; KaLinnikov, V. T. (Koord. Khim. 8 [1982) 39/43; C.A. 96 [1982) No. 95389). 2.4.1.3 MoOF2 ·H20 This hydrate can be prepared by exposure of MoF 4 to water vapor (18 Torr, room tempera ture) and subsequent evacuation of the reaction vesseL to 10-3 Torr. The hydrate water is Lost upon heating in a vacuum forming anhydrous MoOF2 (see above) and no further change of composition takes pLace up to 600°C. Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981) 573/6; Russ. J. (norg. Chem. 26 [1981) 310/2). Gmelin Handbook Mo Suppl. Vol. B 5 MoOF2, MoOF3 191 2.4.1.4 MoOF3 Older data are given in "Molybdän", 1935, p. 151. The MoOF3 was prepared for the first time in 1968 by reacting equimolar quantities of MoOF4 and MoF4 at about 200°C for 8 to 10 h in a sealed quartz ampule according to MoOF4+MoF4"""~MoOF3+MoFs. The MoFs condenses in the cold part of the ampule [1,2]. MoOF3 can also be synthesized by the reaction of MoFs with Mo03 at 180°C. MoOF4 obtained as a side product is removed by vacuum distillation at 120 to 130°C and MoOF3 remains [3]. MoF3 can be oxidized with O2 (-0.8 atm) at 200°C to give X-ray amorphous MoOF3 [4,5]. MoOF3 was mass spectrometrically detected in the saturated vapor generated by heating MoF3 and Mo02F2 above 751 K (in addition to gaseous Mo02F2) [6]. MoOF3 is stable upon heating in a vacuum; sublimation occurs above 250°C [5]. Estimated sublimation enthalpy and entropy values at 298 Kare 182 kJ/mol and 190 J. mol-1. K-1, respec tively [7]. From mass spectrometric data ilHs=56.1±1.3 kcal/mol (~234.7 kJ/mol) has been obtained at 751 K [6]. Estimated thermodynamic data: Heat capacity Cp,298=105 for solid MoOF3 and 75 J, mol-1. K-1 for gaseous MoOF3, The entropy 8298 =132 and 322 J. mol-1, K-1, respectively [7]. Using the rigid rotor-harmonic oscillator approximation the entropy 8'1- and the thermody namic potential (G'I- -H2sa)/T have been calculated for MoOF3(g): 8'1- = 250.9, 323.8, and 459.1 J·mol-1·K-1 for T=100, 298, and 1200 K; (G'I-- H2sa)/T=388.7, 323,8, and 384,2 J. mol-1. K-1, respectively (selected values) [8]. The standard enthalpy of formation of gaseous MoOF3, ilHf.298 (in kcal/mol), was evaluated from the Mo02F2(g) + MoF4(g)~2MoOF3(g) equilibrium studied at 823 K by mass spectrom etry, The value -257.0±6.2 given in the abstract of paper [6] seems to be erroneous. The - 247.0 ± 6.2 given in the text [6] closely agrees with the - 246.0 ± 6,2 given in [9]. Citing [6], ilHf',29B=-2100(?) kJ/mol (~-502 kcal/mol) are given in [7]. ilHf',298=-2282 kJ/mol for solid MoOF3 [7]. The IR spectrum of green, crystalline MoOF3 is plotted for 400 cm-1~v~1200 cm-1 in [3]. Broad absorption bands occur in the 500 to 1000 cm-1 range of dark blue MoOF3 [5]. With this amorphous MoOF3 absorption peaks occur near 1480,1390,1000,830,650, and 480 cm-1 [4]. For tentative assignments of the IR vibrations, see the papers [3, 4]. The following fundamental frequencies (in cm-1, multiplicities in parentheses) have been estimated for the molecule assumed to have C3v symmetry: 995(1), 708(2), 688(1), 242(2), 227(2), and 222(1) [8]. The magnetic susceptibility was determined by the Faraday method. The effective magnetic moment fleff va ries with temperature as follows [10]: fleff in fls ...... 0.42 0.47 0.54 0.57 0.60 0.63 0.67 0.69 0.70 Tin K ...... 80 105 150 178 199 227 259 278 299 COl\lparison with the spin-only value 1.73 fls suggests that MoOF3 exists as a polymer with antiferromagnetic coupling between the MoOF3 units which are assumed to be linked by bridging F atoms [10]. The MoOF3 formation trom MoOF4 and MoF4 above 170°C was studied by EPR. At 160 to 170°C, an intense main line was observed. It is attributed to transitions in Mo atoms with even isotopes as weil as to transitions involving the unresolved ml = ± V2 levels of the odd isotopes. Four weak satellites also observed are attributed to hfs signals from transitions involving the ml = ±312 and ±S/2 levels of the odd Mo isotopes. No EPR signal was observed at 96°C (in the melt) nor at room temperature. Cooling the reacted MoOF4 plus MoF4 mixtures from 180 to -196°C yields a glassy solid. The freezing is accompanied by almost complete disappearance of the EPR signal. This suggests that MoOF3 is associated at low temperatures. The spectrum Gmelin Handbook Mo Suppl. VoL S 5 192 Molybdenum Oxide Fluorides observed near 170°C indicates a splitting factor go = 1.89 and a hyperfine coupling constant ao = 45 ± 2Hz [2]. The enthalpy change ~H29B=163.2 ±8.6 kcaVmol for the reaction MoOF3(g) ~ MoF3(g) + 0 has been calculated using mass spectrometric data of the vapor phase of the MoF3-Mo02F2 system. The following ions occur in the mass spectrum of MoOF3 at 751 K and 70 eV: Mo+(60), MoO+(9), MoF+(4), MoOF+(16), MoF~(6), MoFt(14), MoOF~(34), MoOFj(100) [6]. Treatment of MoOF3 with NH3 at temperatures between -78 and + 35°C yields a dark brown powder of composition MoOF3 ·2NH3, the degree of oxidation for Mo being +5.08 [3]. The enthalpy values ~H29B = - 418.0 ± 20.5 kJ/mol for the reaction MoOF3(g) + F-(g) ~ MoOF4", ~Hm=-24.98 ±4.74 kJ/mol for MoOF3 + BeF3" ~MoOF4" + BeF2, and ~HT=- 205.0±15.1 kJ/mol for MoOF3 + BeF3" ~ BeMoOFs at T = 790 to 900 K have been calculated using mass spectrometric equilibrium data at 840 to 921 K in the vapor generated by reacting MoF3 with KBe2Fs in the presence of small amounts of oxygen [8]. References: [1] Nikolaev, A. V.; Opalovsky [Opalovskii], A. A.; Fedorov, V. E. (Therm. Anal. Proc. 2nd Intern. Conf., Worcester, Mass., 1968 [1969], Vol. 2, pp. 793/810, 800; C.A. 73 (1970) No. 94206). [2] Opalovskii, A. A.; Anufrienko, V. F.; Khaldoyanidi, K. A. (Dokl. Akad. Nauk SSSR 184 [1969) 860/2; Dokl. Chem. Proc. Acad. Sci. USSR 184/189 [1969) 97/9). [3) Blokhina, G. E.; Belyaev, I. N.; Opalovskii, A. A.; Belan, L.1. (Zh. Neorgan. Khim. 17 [1972] 2140/3; Russ. J. Inorg. Chem. 17 [1972)1113/5). [4] Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981)573/6; Russ. J. Inorg. Chem. 26 [1981) 310/2). [5] Pervov, V. S.; Butskii, V. D.; Novotortsev, V. M. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 226; C.A. 89 [1978) No. 208231). [6) Alikhanyan, A. S.; Steblevskii, A. V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978] 2549/52; Russ. J. Inorg. Chem. 23 [1978)1412/3). [7] Dittmer, G.; Niemann, U. (Mater. Res. Bull. 18 [1983) 355/69, 36417). [8) Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi), E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982] 145/56). [9] Alikhanyan, A. S.; Steblevskii, A. V.; Malkerova, I. P.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (5th Vses. Simp. Khim. Neorgan. Ftoridov, Dnepropetrovsk 1978, p. 29; C.A. 90 [1979) No. 29936). [10) Ellert, O. G.; Butskii, V. D.; Novotortsev, V. M.; Pervov, V. S.; Volkov, V. V.; Kalinnikov, V. T. (Koord. Khim. 8 [1982] 39/43; C.A. 96 [1982] No. 95389). 2.4.1.5 MoOF3 ·0.5H20 For preparation of the compound, MoFs is treated with water vapor of 18 Torr at room temperature. The MoOF3 ·0.5H20 is amorphous to X-rays [1]. The magnetic susceptibility was determined by the Faraday method. The effective magnetic moment fleff shows the following temperature dependence [2]: ~eff in ~B .•••...• 0.44 0.52 0.57 0.61 0.61 0.64 0.66 0.68 0.68 0.67 0.71 Tin K ...... 80 123 153 180 197 221 238 250 256 275 299 The low fleff values observed (spin-only value: 1.73 ~B) suggest antiferromagnetic coupling mediated by fluorine bridges in a chain structure [2]. Gmelin Handbook Mo Suppl. Vol. B 5 193 The IR spectrum of the amorphous MoOF3·0.5H20 suspended in Liquid paraffin is plotted for 400 to 1800 cm-1 in the paper [1]. IR absorption maxima near 1630, 970, 730, and 500 cm-1 were assigned to v(H20), v(Mo--O), v(Mo--Fterm), and v(Mo--Fbr), respectively. In addition, two peaks were observed near 1460 and 1390 cm-1 [1]. Upon heating in a vacuum, MoOF3·0.5Hp decomposes with evolution of HF to give MoOF2 and Mo02F2 via M020 3F4 [1]. References: [1] Butskii, V. D.; Pervov, V. S. (Zh. Neorgan. Khim. 26 [1981]573/6; Russ. J. Inorg. Chem. 26 [1981] 310/2). [2] Ellert, 0. G.; Butskii, V. D.; Novotortsev, V. M.; Pervov, V. S.; Volkov, V. V.; KaLinnikov, V. T. (Koord. Khim. 8 [1982] 39/43; C.A. 96 [1982] No. 95389). 2.4.1.6 Mo03_xF.. x=0.2 to 0.97 Two modifications of these compounds are known, namely a blue orthorhombic one with x=0.2 [1] and 0.25 [2], and a gold cubic one with x=0.6 to 0.97 [1,2]. Mo03- xFx can be synthesized under hydrothermal conditions by reacting appropriate amounts of Mo, Mo03, and 48% aqueous HF or anhydrous HF in sealed gold ampules at 700°C and 3 kbar (8 h) [2] or at 500°C and 2 kbar (6 d) [1]. Single phase samples form only in the anhydrous HF systems. They are washed with water and dried in vacuum at 120°C [2]. The orthorhombic modification, which is also formulated as M04011.2FOB [1] and M040 11 F, forms blue needles. Lattice parameters are a = 3.8791 ± 0.0006, b =14.057 + 0.002, c = 3.7225±0.0006A for x=0.25 (a is the needle axis) [2]. For x=0.2, a=3.878±0.005, b= 13.96±0.1, c=3.732±0.005 A; Z=4. Space groupCmcm-D~~ (No. 63). The structure has been elucidated by single crystal investigations and refined to R = 0.091. All the Mo and ° atoms occupy the position 4c (0, y, 0.25, etc.); positional parameters are: atom x y z atom x y z Mo 0 0.1026(0) 0.25 0(2) 0.5 0.4371 (4) 0.25 0(1) 0.5 0.0805(11) 0.25 0(3) 0 0.2208(8) 0.25 Atomic distances and bond angles are [1]: atoms distance in A atoms angle 0(1)-Mo 1.963(3) 0(1 )-Mo--O(1 ') 161.9(0.8t 0(1',l-Mo 1.963(3) 0(2)-Mo--O(2") 146.9(0.3t °(2)-M 0 1.947(2) 0(3)-Mo--O(2') 180° 0(2')-Mo 2.311 (6) 0(1 )-Mo--O(3) 99.4(0.4t 0(2")-Mo 1.947(2) 0(1 )-Mo--O(2) 87.4(0.1t 0(3)-Mo 1.650(11 ) 0(2)-Mo--O(3) 106.5(0.2t Mo--Mo' 3.419(2) 0(2)-Mo--O(2') 73.5(0.2)° M040 11 F is isomorphous with M040 10(OHh (~Ho5Mo03)' see "Molybdenum" Suppl. Vol. B 3a, 1987, p. 11, the structures being very closely related to that of Mo03, but with a tendency towards a more ideal octahedral coordination around the Mo atoms for the fluorine-containing compound [1, 2]. The octahedra are joined by edges to form zig-zag-shaped rows which are GmeLin Handbook Mo Suppl. Val. B 5 13 194 Molybdenum Oxide Fluorides mutually connected by corners to form layers. The layers are stacked so that adjacent layers have no atoms in common [1]. The pycnometrically measured and calculated densities are 4.6 ± 0.1 and 4.70 g/cm3, respectively [1]. The cubic modification forms golden cubes. The lattice parameter a increases with the F content from 3.833 Afor x = 0.74 to 3.844 Afor x = 0.97 [2]. For M002.4Fo.6, a = 3.842 ± 0.003 A; Z=1. The structure was elucidated by powder diffraction; R = 0.12. The d values are given in the paper. Space group Pm3m-O~ (No. 221). The structure is similar to that of Re03 with the Mo atom in anormal octahedral coordination [1,2]. The oxygen and fluorine atoms are considered to be randomly distributed in the position 3 d (0.5, 0, 0) [1]. The measu red and calculated densities are 4.1 ± 0.1 and 4.22 g/cm3, respectively [1]. Electrical resistivity measurements of M040"F crystals parallel to the a axis indicate semiconducting behavior (see the figure in the paper). Single crystals of composition M002.'4FO.86 and M002.03Fo.97 have low resistivity values (=0.05Q· cm) at room temperature indicative of metallic behavior. However, the resistivity definitely decreases with increasing temperature. The thermoelectric power is -14 for x= 0.86 and about -1 [.lV/K for x = 0.97 [2]. M040".2FO.8 is decomposed by 2 N NaOH, Mo02.4FO.6 by 2 N HCI to which a trace of HN03 was added [1]. SampIes are also decomposed by molten sodium peroxide [2]. References: [1] Pierce, J. W.; VIasse, M. (Acta Cryst. B 27 [1971]158/63). [2] Sleight, A. W. (Inorg. Chem. 8 [1969]176411). 2.4.1.7 MoOF4 Older data are given in "Molybdän", 1935, pp. 151/2. 2.4.1.7.1 Preparation. Formation MoOF4 can be prepared from the elements by reacting the heated metal powder with a mixture of fluorine and oxygen in mole ratio 3:1 [1] or 5:1 at 400°C using a flow technique [3]. Volatile products are removed at room temperature by pumping and the compound is purified by vacuum sublimation [1, 2]. Molybdenum powder is treated with a stoichiometric amount of O2 and 20% excess F2 in a closed Ni vessel of 350°C for 8 h. The sublimation is carried out at 170°C in a pyrex vessel [3]. Small amounts of the oxide tetrafluoride can be isolated during the production of MoF6 from the elements [4]. With Mo03 as the starting material, MoOF4 can be produced by fluorination with excess fluorine at 100°C (12 h) [5], or at 300°C [6]. In a continuous F2 stream Mo03 is fluorinated at a temperature in the range 400 to 625°C. The gaseous reaction product containing the MoOF4 is continuously withdrawn from the unreacted oxide and MoOF4 is condensed from the mixture [7]. The fluorination temperature can be decreased, the process accelerated, and the product improved by using MoF6 as the fluorinating agent at pressures of 0.4 to 0.5 atm; e.g., when 0.7 9 Mo03 is treated with 1.9 9 MoF6 at 0.5 atm at 120 to 150°C for 10 to 15 min, MoOF4 with 99% purity is obtained [8]. Preparation from Mo03 and MoF6 at 90°C is described in [9]. The use of fluorine gas can also be avoided in a fused salt synthesis by reacting Mo03 with LiF in an Gmelin Handbook Mo Suppl. Vol. B 5 195 argon or oxygen atmosphere (1 atm). Gaseous MoOF4 forms at temperatures above 300°C. The mole ratio of the intimately mixed LiF and Mo03 is always greater than 5:1 with an additional covering layer of LiF [10]. The hydrolysis of MoFs in anhydrous HF by a controlled amount of H20 at room temperature which gives MoOF4 as the only molybdenum containing compound (see p. 170) can serve for preparation [13]. The water can be generated by adding H3B03 which reacts to give BF3 + H20 [14]. Some reactions of MoFs with oxides yield easily separable products in addition to the solid oxide fluoride and can also be used for the preparation of MoOF4. For instance, a large excess of MoFs is condensed onto a well-dispersed sampIe of B20 3 at -196°C and the mixture slowly warmed to room temperature. During this time reaction occurs with formation of highly volatile BF3 wh ich is periodically vented into an expansion bulb. Upon reaching room temperature the product is refluxed in the presence of excess MoFs for about 1 h to ensure completion of the reaction [11, p. 507]. The simultaneous preparation of MoOF4 and volatile Cr02F2 can be achieved by reacting MoFs with Cr03. The MoFs (11 mmol) is added to Cr03 (24 mmol) by vacuum distillation at -78°C and the mixture heated to 125°C for 12 hand evacuated at room temperature. The MoOF4 is obtained pure via sublimation [12]. Another method is based on the reaction of MoFs with Si02 in anhydrous HF. Typically 3 mmol of MoFs are condensed into a Kel-F reaction tube containing 1.5 mmol of quartz wool and 5 mL of anhydrous HF. The reaction is complete in 2 to 4 h at room temperature. All volatile products are vacuum evaporated and the MoOF4 collected by vacuum sublimation [15]. Halogen exchange of MoOCI4 with anhydrous HF, by wh ich the compound was obtained for the first time (see "Molybdän", 1935, p. 151) can be carried out by a similar procedure as used for the MoFs-BP3 reaction. Excess HF (2 to 3 g) is condensed onto a sampIe of MoOCl4 (0.3 to 0.5 g) at -196°C and then allowed to warm slowly to room temperature. The HCI formed during the reaction periodically vents into an expansion bulb [11, pp. 508,513]. Further Formation Reactions. Molybdenum can be oxidized to MoOF4 and MoFs by heating the metal in the presence of KN03 in anhydrous HF at boiling temperature [16]. Formation of the MoOF4 as a side product takes place during the reaction of MoF5 with Mo03 to produce MoOF3 (see p. 191) and in reactions of MoFs with oxygen-containing compounds, e.g., with B(OTeF5b, carboxylic acids and derivatives, and (CH30hSO, see pp. 172, 177/8, and 179. Also the reaction between equimolar Mo02F2 and XeF2 in anhydrous HF gives MoOF4, see p. 210. In binary molybdenum fluorides, MoOF4 frequently occurs as impurity during the fluorina tion of molybdenum due to oxide coatings, by the partial hydrolysis of the fluorides from moisture contamination, or by the reaction of binary fluorides with glass storage vessels in the presence of HF [11, p. 505]. For the occurrence of MoOF4 as a contaminant in MoF5, see also p.96. References: [1] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568/74,1569). [2] Fawcett, J.; Holloway, J. H.; RusselI, D. R. (J. Chem. Soc. Dalton Trans. 19811212/8, 1216). [3] Holloway, J. H.; Schrobilgen, G. J. (Inorg. Chem. 19 [1980] 2632/40, 2639). [4] Edwards, A. J.; Steventon, B. R. (J. Chem. Soc. A 1968 2503/10, 2503). [5] Blanchard, S. (CEA-R-3194 [1967] 1/7, 1; C.A. 67 [1967] No. 48663). [6] Bougon, R.; Bui Huy, T.; Charpin, P. (Inorg. Chem. 14 [1975]1822/30, 1822). [7] Sherwood, D. W.; Banikiotes, G. C. (U.S. 2695214 [1945/54]; C.A. 19554248). [8] Butskii, V. D.; Ignatov, M. E.; Golovanov, B. V.; Pervov, V. S.; lI'in, E. G.; Buslaev, Yu. A. (U.S.S.R. 1057428 [1982/83]; C.A. 100 [1984] No. 70722). G meli n Hand book Mo Suppl. Vol. B 5 13' 196 MoLybdenum Oxide Fluorides [9] BLokhina, G. E.; BeLyaev,1. N.; OpaLovskii, A. A.; Belan, L. I. (Zh. Neorgan. Khim. 17 [1972] 2140/3; Russ. J. Inorg. Chem. 17 [1972]1113/5). [10] Ward, B. G.; Stafford, F. E. (Inorg. Chem. 7 [1968] 2569/73). [11] Burns, R. C.; O'DonneLL, T. A.; Waugh, A. B. (J. FLuorine Chem. 12 [1978] 505/17). [12] Green, P. J.; Gard, G. L. (Inorg. Chem. 16 [1977]1243/5). [13] Selig, H.; Sunder, W. A.; SchiLLing, F. C.; FaLconer, W. E. (J. FLuorine Chem. 11 [1978] 629/35,631). [14] Hoskins, B. F.; Linden, A.; O'DonneLL, T. A. (Inorg. Chem. 26 [1987] 2223/8). [15] Paine, R. T.; McDoweLL, R. S. (Inorg. Chem. 13 [1974] 2366/70). [16] Wiechert, K. (Z. Anorg. ALLgem. Chem. 261 [1950] 310/23, 322). 2.4.1.7.2 Moleeules The main neutraL species in the vapor over MoOF4 is the monomer, but there appearto exist <10 moL% of oLigomeric species (tetramer?) which on (70 eV) eLectron impact fragment yieLding the (MoOF3)t ions observed by mass spectroscopy. OLigomers are aLso indicated by weak IR absorption bands at 542 cm-1 (attributed to fLuorine bridges) and weak bands at 680 and 750 cm-1. Their oLigomer origin was indicated by their intensity vs. pressure dependence recorded near 320 K [1]. The obsoLete concLusion that the gas phase consists of monomers onLy [2, 3] was based on gas phase density measurements between 231 and 414°C [2] and the vapor IR spectrum which was assigned to monomer vibrations in [3, 4]. See aLso the discussion in [1, p.2368]. Monomeric MoOF4• The point group C4V is consistent with the observed IR spectrum [1]. It was aLso adopted in the anaLysis of the photoeLectron spectrum [5]; see aLso [15]. (The point group C2v was adopted in the discussion of the fundamentaL frequencies [6] and in thermody namic caLcuLations [14].) Atomic distances and bond angLes have been determined byeLectron diffraction at pressures beLow 3 x1Q-5 Torr on MoOF4 vaporized at 70 to 80°C [7]: bond ...... Mo-F Mo-O F-P) F-Fb) distance in A ...... 1.836 ± 0.003 1.650 ± 0.007 2.522 ± 0.005 3.563 ± 0.008 a) Edge of square. - b) DiagonaL of square. The bond angLes O-Mo-F=103.8±0.6° and F-Mo-F=86.7±0.3° have been given [7]. P-R branch spacings have been derived for the MO--0 and Mo-F stretches by anaLysis of the IR absorption contours. The resuLts were consistent with MO--0 and Mo-F distances of 1.65 and 1.84 A, respectiveLy, and O=Mo-F angLes of 100° [1]. The moments of inertia (in u· N) are 168.98, 206.63, and 210.40 for x, y, and z, respectiveLy, their product being Ix·ly ·lz =7350000u3·AB (~3.36x10-113g3·cm6) [14]; see aLso [15]. The rotationaL constants B = 0.096 and C = 0.068 cm-1 are assumed. For the Mo-F stretch v7(E), the CorioLis constant ~7 = 0.1 0 ± 0.03 was evaLuated from the P-R branch spacing of V7 [1]. The foLLowing set of force constants (in mdyn/A) fits the IR spectra of MoOF4 : f R =8.813, f, = 4.318, and f" 'cis = 0.485; f"'l,ans = 0.5f"'cis' f R,,=- O.1f"'CiS with R: Mo-o and r: Mo-F [11]. The vaLues fR =8.79 [8] and 9.05 [12] and f,=4.50 [8] and 4.36 [12] have aLso been given, any other force constant being at least one order of magnitude weaker [8, 12]. For mean ampLitudes of displacements aLong the bond distances determined by eLectron diffraction, see [7]; for caLcuLated mean square ampLitudes see [8,12]. Using the geometricaL data of [7] and the IR Gmelin Handbook Mo Suppl. Vol. B 5 197 frequencies from [1, 2], the following fundamental frequencies were calculated [9] and are compared with measured data from [2]: vibration ...... Vl V2 V3 V4 Vs V6 V7 va Vg symmetry type ...... Al Al Al B1 B1 B2 E E E calculated frequency in cm-1 [9] ...... 1048 716 262 623 285 315 718 294 236 measured frequency in cm-1 [2] ...... 1048 714 264 720 294 236 (See also the vibrational spectra given on pp. 200/1.) The electron affinity EA= 4.0 ± 0.4 eV was derived from gas-phase reactions of MoOF n species with BeF2, BeF3" , and Uke species [10]. The following vertical ionization potentials IP have been measured by photoelectron spectroscopy using 21.21 eV radiation: IP=14.3, 14.59, (15.1), 15.41, 15.92, 16.48, 17.4, 17.8, and 18.5 eV. For a tentative assignment of these IPs to orbitals of the MoOF4 moleeule, see the paper [5]. From the thermochemical data, the bond dissociation energies D(Mo=ü) = 739 kJ/mol and D(Mo-F) =449 kJ/mol have been obtained for the gaseous MoOF4 [13]. References: [1] Paine, R. T.; McDowell, R. S. (Inorg. Chem. 13 [1974] 2366/70). [2] Alexander, L. E.; Beattie, I. R.; Bukovszky, A.; Jones, P. J.; Marsden, C. J.; van Schalkwyk, G. J. (J. Chem. Soc. Dalton Trans. 1974 81/4). [3] Edwards, A. J.; Jones, G. R.; Steventon, B. R. (Chem. Commun. 1967 462/3). [4] Ward, B. G.; Stafford, F. E. (lnorg. Chem. 7 [1968] 2569/73). [5] Vovna, V. 1.; Dudin, A. S.; Kleshchevnikov, A. M.; Lopatin, S. N.; Rakov, E. G. (Koord. Khim. 7 [1981] 575/80; Soviet J. Coord. Chem. 7 [1981] 286/91). [6] Rakov, E. G.; Sudarikov, B. N.; Marinina, L. K. (Tr. Mosk. Khim. Tekhnol.lnst. No. 71 [1972] 21/4; C.A. 80 [1974] No. 101902). [7] lijima, K. (BulI. Chem. Soc. Japan 50 [1977] 373/5). [8] Mahmoudi, S.; WendUng, E. (Rev. Chim. Minerale 15 [1978] 254/67). [9] Osipova, G. E.; Yurchenko, E. N.; Kokovin, G. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Ser. Khim. Nauk 1984 No. 8, pp. 11/6; C.A. 101 [1984] No. 139913). [10] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982] 145/56). [11] Levason, W.; Narayanaswamy, R.; Ogden, J. S.; Rest, A. J.; Turff, J. W. (J. Chem. Soc. Dalton Trans. 1981 250117). [12] Bobkova, V. A.; Aleshonkova, Yu. A. (Deposited Doc. VINITI-4039-83 [1983]1/17; C.A. 101 [1984] No. 160263). [131 Burgess, J.; Haigh, 1.; Peacock, R. D. (.J. Chem. Soc. Dalton Trans. 1974 1062/4). [14] Rakov, E. G.; Koshechko, L. G.; Sudarikov, B. N.; Mikulenok, V. V. (Tr. Mosk. Khim. Tekhnol. Inst. No. 71 [1972] 25/7; C.A. 80 [1974] No. 100792). [15] Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonald, R. A.; Syverud, A. N. (JANAF Thermochemical Tables 3rd Ed., Pt. 11 [1985]1138). G melin Handbook Mo Suppl. Vol. B 5 198 Molybdenum Oxide Fluorides 2.4.1.7.3 Crystallographic Properties In the solid state, MoOF4 forms a ehain strueture [1, 2] and a trimerie ring strueture [3]. The existenee of these and possibly other polymerie forms is supported by the Raman speetra for sublimed MoOF4 and MoOF4 obtained by erystallization of the mett, eaeh indieating a different strueture [4]. A polymorphie transition at about 3°C is deteeted by thermal methods [5]. Crystals of MoOF4 grown from the melt are monoelinie with lattiee parameters a = 5.50 ±0.01, b =16.98 ±0.02, e = 7.84 ±0.01 A; [3= 91.7 ±0.3°; Z=8. Spaee group P21/e-Qh (No. 14). The strueture was investigated by single erystal methods and refined by three dimensional least-squares methods, the final R being 0.102 for 1909 independent refleetions. All atoms oeeupy the general position 4e; atomie positions: atom x y z Mo(1) 0.2663(2) 0.1123(1 ) 0.3989(1) Mo(2) 0.7479(2) 0.1412(1 ) 0.0158(1 ) F(1) 0.2975(20) 0.2160(7) 0.4628(13) F(2) 0.2566(20) 0.0278(6) 0.2565(12) F(3) 0.5696(21) 0.0865(7) 0.4811 (14) F(4) 0.0023(17) 0.1510(5) 0.2543(12) F(5) 0.7896(19) 0.2477(6) 0.0370(13) F(6) 0.7420(19) 0.0392(6) 0.0950(13) F(7) 1.0359(25) 0.1276(8) - 0.0848(16) F(8) 0.4985(17) 0.1580(5) 0.1851(11) 0(1) 0.1034(24) 0.0794(8) 0.5573(16) 0(2) 0.5692(27) 0.1368(8) - 0.1521 (18) The struetural unit of MoOF4 eonsists of two erystallographieally distinet oetahedra in whieh the bond lengths and angles are the same within experimental error, see Fig. 49. The bond lengths fall into four groups: d(Mo-O) =1.64 A, the distanee from Mo to terminal F: 1.82 A, and to the two bridging F atoms: 1.94 and 2.29 A. Other atomie distanees are listed in the paper. The angle Mo-F-Mo is 151°. The light atoms are in positions eonsiderably distorted from close paeking. The oetahedra are linked by eis-bridging fluorine atoms to form endless ehains parallel to the a axis. The fluorine bridge is asymmetrie but the oetahedra formed by the light 0(1) Fig.49. The asymmetrie unit of MoOF4 in pro jeetion down [010] [1]. Gmelin Handbook Mo Suppl. Vol. B 5 199 atoms are aLm ost undistorted, with the Mo atoms dispLaced from the centers of the octahedra towards the terminaL oxygen atoms. The most significant feature of the strueture is the singLe, very short, terminaL bond Length between Mo and 0 in eaeh oetahedron (1.64 A) whieh is of the order expected for a Mo-O multipLe bond [1], see aLso [2]. It was shown that the MoOF4 units can be Linked either as endLess ehains or trimeric rings without disturbing the geometry around the metaL atom. A hexagonaL form of MoOF4 with unit ceLL dimensions a = 8.95 and c = 7.91 A, almost isodimensional with a trimerie form of TcOF4, has been found [3]. References: [1] Edwards, A. J.; Steventon, B. R. (J. Chem. Soe. A 1968 2503/10). [2] Edwards, A. J.; Jones, G. R.; Steventon, B. R. (Chem. Commun. 1967462/3). [3] Edwards, A. J.; Jones, G. R.; Sills, R. J. C. (Chem. Commun. 1968 1177/8). [4] Beattie, I. R.; Livingston, K. M. S.; ReynoLds, D. J.; Ozin, G. A. (J. Chem. Soe. A 19701210/6, 1214/5). [5] KhaLdoyanidi, K. A.; YakovLev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981] 3067/9; Russ. J. Inorg. Chem. 26 [1981] 639/40). 2.4.1.7.4 Other Physical Properties The caLcuLated density Dx = 3.41 g/cm3 [1]. Melting. Boiling. Vaporization. The meLting point was found at 95 [2]. 97 [1,3]. and 98°C [4]. see aLso [5]. SoLution of the vapor pressure equation yieLds a tripLe point at 97.2°C and 28.8 Torr in good agreement (± 0.2 K) with the meLting point observed direetLy in thin-waLLed eapiLlaries [3]. The boiLing point is given as 180 [6] and 186°C [1,3]. The vapor pressure p (in Torr) is given for the solid between 40 and 95°C by Log P = 9.21- 2854/T (T in K) [3]. At 23°C, P <0.5 Torr [7]. For the Liquid, Log p = 8.716 - 2671/T, vaLid between 95 and 185°C [3]. At 120°C, p=83 Torr [8]. From the sLope of the vapor pressure eurve, the enthaLpies of subLimation and vaporization were determined as AHsub =13.11 kcaVmoL and AH vap =12.09 keaVmoL, respeetiveLy. For the fusion, AHm=AHsub-AHvap=1.02 keaVmoL [3]. Estimated vaLues for 298 Kare AHsub =69 [9], 70 kJ/moL (~17 kcaVmoL) and AHvap =49 kJ/moL (~12 keaVmoL) [10]. The corresponding entro pies are ASm= 2.768 and ASvap = 26.3 caL· moL-l. K-l [3]; ASsub.298 =180 J. moL-l. K-l (~43 eaL· moL- 1 ·K-l) and ASvaP.298=111J·moL-l·K-l (~26 eaL·moL-l·K-') [10]. Further Thermodynamic Data. For solid MoOF4 , Cp.298=127J·moL-l·K-l and S298= 151'J· moL-l. K-1 have been estimated [10]. FoLLowing are data for gaseous MoOF4. Using the rigid rotor-harmonie oseiLlator approxi mation, thermodynamic data have been caleulated for 100 to 6000 K [11] and for Cp between 298 and 2500 K [12], see also [13]. Cp' So, -{Go- H~8)/T, and w- H~8 are listed forthe ideal gas between 0 and 6000 K [14]. For C~.298 the value 23.585 cal· mol-1 • K-1 (~98.680 J. mol-1 • K-l) is given [11] and 99.04 J. mol-1 • K-l is caLeuLated [12] and compared with the measured value 98.66 [15]. Cp.298 =96.74J·mol-1 ·K-l [14]; 21.73eal·mol-1 ·K-1 (~90.92J·mol-l·K-l) [13]. To within ± 0.31 J. mol-1 • K-l, Cp may be represented between T = 298 and 2500 K by Cp = a + b/T + c ln T with a=185.43, b=-15584.9, and c=-13.883 [12]. Gmelin Handboak Mo Suppl. Val. B 5 200 Molybdenum Oxide Fluorides H298 =4.641kcalJmol and S2s8=78.323cal·mol-1·K-l (~327.70J·mol-l·K-l) [11). S298= 328.70 J. mol-1. K-l is calculated [12] and compared with the measured value 327.70 J. mol-1. K-1 [15]. S2s8 =330.617 J. mol-1. K-l [14]; 77.04 cal· mol-1. K-l (~322.34 J. mol-1. K-1) [13]. Thermodynamic Data o( Formation.The standard enthalpy of formation of solid MoOF4 was determined by hydrolysis calorimetry using aqueous NaOH. The result ßHf.298.2=-1380 kJ/mol [9] confirms the value -329±5kcalJmol (~-1376 kJ/mol) estimated earlier using thermody namic data of Mo03 and MoFs and applying heuristic rules [16]. For gaseous MoOF4 , ßHf.298.15=-1255.200 kJ/mol [14]. Also for gaseous MoOF4 , but for formation from the atoms, the value -2535 kJ/mol is given [9]. ßGj.298.15=-1193.739 kJ/mol and log K'.298.15 = 209.138 [14]. Values for ßHj, ßGj, and log K, are listed between 0 and 6000 K for the ideal gas in [14]. Vibrational Spectra. Solid MoOF4 . The IR spectrum of the powder was recorded at room temperature in the range 400to 4000 cm-1. Fora plot upto -1150 cm-1, see the paper [1]; also see [17]. The Raman spectra differ for solid MoOF4 obtained by vacuum sublimation and MoOF4 obtained by cooling the melt. Unfortunately, the paper fails to indicate which prepara tion yielded wh ich spectrum. The following Raman shifts (in cm-1) are reported [18]: preparation I · ...... 1039s 716mw 692vw, sh 661 m preparation 11 ...... 1042s 740m 721 mw 668s preparation I ...... 530vw 506vw 334w,sh preparation 11 · ...... 571w 529w 506vw 333m preparation I ...... 316mw 308mw 258m 244w,sh preparation 11 · ...... 309ms 275w preparation I ...... 172w 122w preparation 11 ...... 222m 216vw,sh Liquid MoOF4 . Raman shifts (in cm-1) have been reported for the melt as folIows: Ref. [19] 1039s,pol 713s,pol 666m,pol 506vw 311 m 240w,br Ref. [18] 1038s,pol 712s,pol 665m,pol 310m 244vw,br The Raman spectrum is plotted for 50 cm-1;:2v;:21100 cm-1 in [18]. Vapor. The IR spectrum of MoOF4 vapor at 300 K was recorded between 400 and 2000 cm-1. The v2(A1) mode (an Mo-F stretch) obviously nearly coincides in frequency with the v7(E) mode (another Mo-F stretch). The vl(A1) mode (the Mo=ü stretch) and one of the Mo-F stretches have similar absorption contours with P-R spacings of 18 to 19 cm-1. The second Mo-F stretch has a P-R spacing of 13.5 to 14.5 cm-1. The peak absorptivity of the V1 mode is 14% of that in the -721 cm-1 band (V2 + V7)' The following frequencies are accurate to within ±0.5 cm-1 for the Q branch maxima. The P, Q, and R branch maxima for Vl (Mo=O stretch) occur at 1039, 1048.6, and 1058 cm-l, respectively. For the -721 cm-1 band, the contour of wh ich is perturbed, 720.8 cm-1 are given for the Q branch maximum of V7 (Mo-F stretch). Bands at 542 (vw), 680 (w), and 750 (w) cm-1 have been identified as oligomer bands by the pressure dependence of their intensity. The 542 cm-1 band is attributed to fluorine bridges [7]. Bands at 530, 680, 720, and 1045 cm-1 were found in the IR spectrum between -435 and -1110 cm-1 and are plotted in [8]. Between 4000 and 400 cm-l, the following bands were found at v (in cm-1): 1045sh,w, 1032, 1025, 1020vs, 750sh,w, 725, 718vs, 630m, and 540vw Gmelin Handbook Mo Suppl. Vol. B 5 201 [20]; see aLso the IR spectrum recorded at :s100°C and plotted for the range ~1100 to ~500 cm-1 in [1]. The IR data given in [21] are obviousLy obsoLete. The foLLowing IR frequencies and Raman shifts (in cm-1) are given in [19]: IR ...... 1048m (paR) 720vs,br - 294w (paR) 264w (paR) 236w{PR) Raman ...... 1047m,poL 714s,poL 308m,br Matrix IsoLated MoOF4 • At diLutions of ~1 :1000, the foLLowing IR band positions (in cm-1) have been found [22]: vl{A1) vs{E) v9{E) in N2 matrix ...... 1050 309/304 238 in Ar matrix ...... 1045 301 232 (The Vl and V7 frequencies given indicate the centers of compLex absorption bands due to isotope fine structure [22].) With an Ar matrix, IR bands at (in cm-1) 716 (s), 301 (w), 259 (m), and 233 (m) have been found in the 800 to 200 cm-1 range [19]. For vibrationaL progressions observed by UV absorption [22], see UV-visibLe spectra beLow. The IR spectra are consistent with isoLation of monomers. The N2 matrix apparentLy yields a singLe MoOF4 site, the symmetry of wh ich is Low according to the broad absorption features which indicate partiaL lifting of the degeneracies (note the spLitting of vs). The spectra from the Ar matrix, on the other hand, indicate two trapping sites (A and B) both of which are highLy symmetric. The deconvoLution of the spectra into features due to A sites and features due to B sites is indicated in the spectra plotted in the paper. The foLLowing isotope fine structure is given for the Vl (MO--o stretch) and V7 (Mo-F stretch) modes (v in cm-1) [22]: isotope ...... 92Mo 94Mo 95Mo 96Mo 97Mo 9sMo lOOMo V1, N2 matrix ...... 1052.9 1051.1 1050.3 1049.4 1048.6 1047.8 1046.2 Vl' Ar matrix, site A 1047.9 1046.0 1045.2 1044.4 1043.6 1042.8 1041.3 V7' Ar matrix, site A .. 716.5 714.4 713.3 712.3 711.3 710.3 708.4 UV-Visible Spectra. The absorption spectrum of MoOF4 isolated (-1 :2000) in an N2 matrix at 12 K is plotted from ~ 226 to 350 nm [22]. There are two absorption bands at 39150 and 44250 cm-1• Using the procedure given in [23] the lowest energy 0 ~ Mo and F ~ Mo charge transfers have been calculated as 31000 ± 2000 and 42000 ± 2000 cm-1, respectively. The 39150 cm-1 absorption (attributed to F ~ Mo charge transfer) shows the foLLowing vibrationaL progression (in cm-1): 41390, 40540, 39870, 39150, 38580, 37950, 37370, 36710, 36100, 35390, 34690, 33990, 33330 yielding an average v' of 670 ± 70 cm-1 [22]. References: [1~ Edwards, A. J.; Steventon, B. R. (J. Chem. Soc. A 1968 2503/10). [2] Holloway, J. H.; Laycock, D. (Advan. Inorg. Chem. Radiochem. 28 [1984] 73/99, 78). [3] Cady, G. H.; Hargreaves, G. B. (J. Chem. Soc. 1961 1568174, 1570). [4] Vasil'ev, Va. V.; Opalovskii, A. A.; Khaldoyanidi, K. A. (Izv. Akad. Nauk SSSR Ser. Khim. 1969 271/5; Bull. Acad. Sci. USSR Div. Chem. Sci. 1969 231/3). [5] Green, P. J.; Gard, G. L. (Inorg. Chem. 16 [1977]1243/5). [6] Edwards, A. J.; Peacock, R. D.; SmalI, R. W. H. (J. Chem. Soc. 1962 4486/91, 4487). [7] Paine, R. T.; McDoweLL, R. S. (Inorg. Chem. 13 [1974] 2366170). [8] Blanchard, S. (CEA-R-3194 [1967]1/12; C.A. 67 [1967] No. 48663). [9] Burgess, J.; Haigh, 1.; Peacock, R. D. (J. Chem. Soc. Dalton Trans. 1974 1062/4). [10] Dittmer, G.; Niemann, U. (Mater. Res. BuLL. 18 [1983] 355/69, 366/7). Gmelin Handbook Mo Suppl. Vol. B 5 202 MoLybdenum Oxide Fluorides [11) Kovba, V. M.; YampoL'skii, V.I.; MaL'tsev, A. A. (Vestn. Mosk. Univ. Ser.1I Khim.16 [1975) 508; C.A. 83 [1975) No. 198658, Deposited Doc. VINITI-1050 [1975)). [12) Osipova, G. E.; Yurchenko, E. N.; Kokovin, G. A. (Izv. Sibirsk. Otd. Akad. Nauk SSSR Sero Khim. Nauk 1984 No. 8, pp. 11/6; C.A. 101 [1984) No. 139913). [13) Rakov, E. G.; Koshechko, L. G.; Sudarikov, B. N.; MikuLenok, V. V. (Tr. Mosk. Khim. Tekhnol. Inst. No. 71 [1972) 25/7; C.A 80 [1974) No. 100792). [14) Chase, M. W., Jr.; Davies, C. A.; Downey, J. R., Jr.; Frurip, D. J.; McDonaLd, R. A; Syverud, AN. (JANAF ThermochemicaL TabLes 3rd Ed., Pt. 11 [1985)1138). [15) Kovba, V. M. (Diss. Moscow State Univ. 1976 as cited in [12)). [16) Rakov, E. G.; Marinina, L. K.; Sudarikov, B. N.; Koshechko, L. G.; Fedorov, G. G. (Tr. Mosk. Khim. Tekhnol. Inst. No. 65 [1970) 28/30; C.A. 76 [1972) No. 104691). [17) BLokhina, G. E.; BeLyaev, I. N.; OpaLovskii, A. A.; Belan, L.1. (Zh. Neorgan. Khim. 17 [1972) 2140/3; Russ. J. Inorg. Chem. 17 [1972)1113/5). [18) Beattie, I. R.; Livingston, K. M. S.; ReynoLds, D. J.; Ozin, G. A. (J. Chem. Soc. A 1970 1210/6). [19) ALexander, L. E.; Beattie, I. R.; Bukovszky, A; Jones, P. J.; Marsden, C. J.; van SchaLkwyk, G. J. (J. Chem. Soc. DaLton Trans. 197481/4). [20) Edwards, A. J.; Jones, G. R.; Steventon, B. R. (Chem. Commun. 1967462/3). [21) Ward, B. G.; Stafford, F. E. (Inorg. Chem. 7 [1968) 2569/73). [22) Levason, W.; Narayanaswamy, R.; Ogden, J. S.; Rest, A J.; Turff, J. W. (J. Chem. Soc. DaLton Trans. 1981 2501/7). [23) So, H.; Pope, M. T. (Inorg. Chem. 11 [1972)1441/3). 2.4.1.7.5 Electrochemical Behavior The eLectrochemicaL behavior of MoOF4 in anhydrous HF at Pt eLectrodes was studied by cycLic voLtammetry, aLternating current, and the second harmonie techniques. In neutraL medium (0.5 M KBF 4 in anhydrous HF) one weLL-defined reduction wave with a haLf-wave potentiaL EV2 of 0.47 V appears. The reduction invoLves fast eLectron transfer between two reLativeLy simpLe species and can be described by MoOF4 + e-~ MoOF4. The addition of NaF to this soLution has no effect on either the position or the shape of the reduction wave. The potentiaL of the MoOF4/MoOF4 coupLe is such that MoOF4 is a stronger oxidant than either MoF6 or WF6. Bond, A. M.; Irvine, 1.; O'DonneLL, T. A. (Inorg. Chem. 16 [1977) 841/4). 2.4.1.7.6 Chemical Reactions Decomposition. For the decomposition according to MoOF4(g) -> MoOF3(g) + F the enthaLpy of reaction '\H~B = 86.3 ± 7.0 kcaUmoL has been caLcuLated from mass-spectrometric data of the MoF3-Mo02F2 system at 751 K [1). Reactions with Electrons. In the poLyisotopic mass spectrum of MoOF4 recorded at 70 eV ionization energy the foLLowing ions appear (reLative abundances in parentheses): Mo+ (11), MoO+(8), MoF+(8), MoOF+(11), MoFt(13), MoOFt(14), MoFt(11), Mo02Ft«1), MoOFt(100), MoFt«1), MoOFt«1), (MoOF3)t(4). Spectra at 20 eV show about 30% greater intensity of the MoOFt species [2). Gmelin Handbook Mo Suppl. Vol. B 5 203 Reactions with Elements. Thermodynamic data for the reaction MoOF4(g) + 3 H2~ Mo + H20(g) + 4 HF(g) have been determined for temperatures in the range 298 to 1500 K. The reduction is sLightly exothermic. At a stoichiometric ratio of the reagents the reduction yield approaches 100%. Selected values for ~W, ~GD, and log Kp [3]: Tin K ...... 298 500 700 900 1100 1300 1500 - ~W in kcal/mol ...... 1.9 3.0 4.4 5.9 6.9 7.9 _~GD in kcal/mol ...... 15.1 24.7 33.3 41.8 50.2 58.0 65.2 log Kp ...... 11.1 10.8 10.6 10.5 10.0 9.8 9.5 The fluorination of MoOF4 to produce the hexafluoride was shown to be thermodynamically possible; ~H~s =- 56 kcal/mol was estimated for the reaction MoOF4(g) + F2~ MoF6(g) + 0.5 O2 [4]. Insertion of MoOF4 into graphite proceeds more easily than that of MoF6 (see p. 167). Upon heating a mixture of the solid components at 11 ODC (2 d) the first stage graphite intercalation compound forms. The composition of the bluish black product corresponds to the formula Cs.sMoOF4 [5]. In the presence of Cr02F2 the insertion is faciLitated. With appreciable amounts of Cr02F2 formation of an MoOF4: Cr02F2=1:1 compound between the graphite layers of composition C19MoOF4Cr02F2 forms at 110DC within 15 h [6]. Reactions with Inorganic Compounds. The enthalpy of hydrolysis in 1 M or 0.1 M aqueous NaOH, ~H =- 425(5) kJ/mol, is calorimetrically determined for crystalline MoOF4 [7]. With liquid ammonia, MoOF4 forms an orange colored product which turns to dark brown when the Liquid is removed. By chemical analysis the composition MoOF4·4.5 NH3 is stated for the brown solid [8]. The reaction with stoichiometric amounts of XeF2 at 50 to 60 D C yields adducts XeF2· nMoOF4 with n=1 or 2 (see p. 239) [9]. MoOF4 is fairly soluble in anhydrous liquid HF [10]. In contrast to WOF4, the molybdenum compound shows no appreciable Lewis acidity in anhydrous HF [11]. Both the Raman and the 19F NMR spectrum give evidence for a partial exchange between HF and the dissolved species yielding the dimeric anion M020 2Fg. However, the extent of ionization of MoOF4 is small [12]. Formation of MoOFs ions in solutions of MoOF4 in HF could not be detected by Raman spectroscopy or by conductivity measurements [13], but was inferred from the Raman spectrum of the hydrolysis products of MoF6 in HF [14]. For the solutions in HF see also the next section. With the strong base nitrosyl fluoride, NOF, the adducts (NO)M020 2F9, (NOhMoOF6, and (NO)MoOFs form. Similarly, with ClOF3, MoOF4 gives the adducts ClOF2MoOFs and ClOF2MoP2F9 at room temperature. In a fresh solution of MoOF4 in ClF3 the ions M020 2Fg and ClF~ are detected by Raman and 19F NMR spectroscopy. After a few months, MoOF4 is completely converted into MoF6. No reaction occurs with ClFs at room temperature within a period of a few days [12]. Halogen exchange with BCl3 at room temperature yields MoOCl4, BF3, and mixed chloride fluorides of boron [10]. When MoOF4 is dissolved in a fivefold excess of SbFs at 40 to 50DC and the excess SbFs is removed at room temperature under a dynamic vacuum, a colorless solid adduct of composi tion MoOF4·SbFs is obtained. The Raman spectrum of the solid product indicates a sLight contribution of an ionic formulation such as [MoOF3]+[SbF6]-. There is also evidence for a second adduct of composition MoOF4·2SbFs [15]. Gmelin Handbook Mo Suppl. Vol. B 5 204 MoLybdenum Oxide FLuorides Thermographie studies of mixtures of MoOF4 with aLkali fluorides show great tendencies for the formation of M[MoOF5J, where M = K, Rb, or Cs (16). MoOF4 and Mo03 react at 180 to 200°C to produce pure Mo02F2 (16). With equimoLar amounts of MoF4 at temperatures above 170°C, MoOF3 and MoF5 form. This reaction can be used for the synthesis of both MoF5 and MoOF3 (see pp. 96 and 191, respectiveLy) [16, 17). The equiLibrium diagram of the MoOFc MoF5 system shows the formation of solid soLutions over the whoLe range of concentration, see Fig. 50 (18), which was predicted from the structuraL simiLarity of the components (19). The formation of MoOF3 in this system above 165°C resuLts from the disproportionation of MoF5 into gaseous MoFs and solid MoF4 foLLowed by the reaction MoF4 + MoOFc~ MoOF3 + MoF5 (17). MoOF4 is fairLy soLubLe in Liquid MoFs (10). 100,...------, ;-' 60 c Fig. 50. EquiLibrium diagram of the MoOFc MoF5 system (18). References: (1) ALikhanyan, A. S.; StebLevskii, A. V.; Pervov, V. S.; Butskii, V. 0.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 (1978) 2549/52; Russ. J. Inorg. Chem. 23 (1978)1412/3). (2) Paine, R. T.; McOoweLL, R. S. (Inorg. Chem. 13 (1974) 2366/70). (3) Rakov, E. G.; KoLzunov, V. A; Sudarikov, B. N. (Tr. Mosk. Khim. TekhnoL. Inst. No. 85 (1975) 40/1; C. A 85 (1976) No. 146333). (4) Rakov, E. G.; Marinina, L. K.; Sudarikov, B. N.; Koshechko, L. G.; Fedorov, G. G. (Tr. Mosk. Khim. TekhnoL. Inst. No. 65 (1970) 28/30; C. A 76 (1972) No. 104691). (5) Hamwi, A; Touzain, P. (Rev. Chim. MineraLe 19 (1982) 432/40, 438/9). (6) Hamwi, A; Touzain, P.; Bonnetain, L. (Rev. Chim. MineraLe 19 (1982) 651/62, 655). (7) Burgess, J.; Haigh, 1.; Peacock, R. O. (J. Chem. Soc. OaLton Trans. 1974 1062/4). (8) BLokhina, G. E.; BeLyaev, I. N.; OpaLovskii, A. A.; Belan, L. I. (Zh. Neorgan. Khim. 17 (1972) 2140/3; Russ. J. Inorg. Chem. 17 (1972) 1113/5). (9) HoLLoway, J. H.; SchrobiLgen, G. J. (Inorg. Chem. 19 (1980)2632/40,2639; Inorg. Chem. 20 (1981) 3363/8). (10) Burns, R. C.; O'OonneLL, T. A.; Waugh, A. B. (J. FLuorine Chem. 12 (1978)505117, 508, 511, 515). (11) Bond, A. M.; Irvine, 1.; O'OonneLL, T. A. (Inorg. Chem. 16 (1977) 841/4). (12) Bougon, R.; Bui Huy, T.; Charpin, P. (Inorg. Chem. 14 (1975)1822/30, 1823/4, 1829/30). (13) Paine, R. T.; Quarterman, L. A. (Inorg. NucL. Chem. H. H. Hyman Mem. VoL. 197685/6). (14) Selig, H.; Sunder, W. A.; SchiLLing, F. C.; FaLconer, W. E. (J. FLuorine Chem. 11 (1978) 629/35, 634). (15) Fawcett, J.; HoLLoway, J. H.; RusseLL, O. R. (J. Chem. Soc. OaLton Trans. 19811212/8, 1212, 1217). GmeLin Handbook Mo Suppl. Vol. B 5 205 [16] Nikolaev, A. V.; Opalovsky [Opalovskii], A. A.; Fedorov, V. E. (Therm. Anal. Proc. 2nd Intern. Conf., Worcester, Mass., 1968 [1969], Vol. 2, pp. 793/810, 800, 809; C.A. 73 [1970] No. 94206). [17] Opalovskii, A. A.; Anufrienko, V. F.; Khaldoyanidi, K. A. (Dokl. Akad. Nauk SSSR 184 [1969] 860/2; Dokl. Chem. Proc. Acad. Sci. USSR 184/189 [1969] 97/9). [18] Khaldoyanidi, K. A.; Yakovlev, I. 1.; Ikorskii, V. N. (Zh. Neorgan. Khim. 26 [1981]3067/9; Russ. J. Inorg. Chem. 26 [1981] 1639/40). [19] Krause, R. F., Jr.; Douglas, T. B. (J. Chem. Thermodyn. 9 [1977]1149/63, 1162). 2.4.1.7.7 Solutions Solutions in HF. The electrical conductivity of the 0.1 M solution (not saturated) was studied at O°C. The specific conductivity a = 2.84 x 1O-S Q-l. cm-1 results when corrected for that of the solvent (0.918 x1O-S Q-l· cm-l). The equivalent conductivity !-l= 0.28Q-l· cm-l. mol-1 and a degree of ionization a = 0.07% results [1]. Saturated (at 25°C) solutions of MoOF4 in anhydrous HF show a strong, polarized Raman band at 733cm-1 [1]. In solutions with MoOF4:HF mole ratios between 0.26 and 0.015, in addition to the bands from dissolved MoOF4 (main features: Mo=O stretch at 1041 cm-1 and symmetric in-plane Mo-F stretch at 706 cm-1) a pronounced shoulder at 1022 cm-1 occurs growing in intensity with increasing dilution at 10°C. The 1022 cm-1 feature is attributed to MOP2F9 formed according to 2MoOF4+2HF~M0202Fg+H2F+. 19F NMR indicates shifts (Ö>O implies upfield shifts) of -142.7 ppm for MoOF4 and +197.9 ppm for HF (with respect to CCl3F). At 15°C the features due to M020 2Fg are more distinct [2]. A shift of ö =-146 ppm in the 19F NMR spectrum relative to CCl3F is given in [3]. Reactions in Other Nonaqueous Solutions. In solvents L having donor properties (e. g. CH 3CN) the weak Lewis acid MoOF4 forms adducts MoOF4· L in which the four F atoms lie in the equatorial plane of an octahedron and L in trans position to the oxygen atom [4]. Also dimeric anions, M020 2Fg, with fluorine bridged Mo atoms have been identified with fluoride ion donors, e. g. with HF in CH3CN [5], see also above. A 6 mol% MoOF4 solution in propylene carbonate at 16°C shows in the 19F NMR a downfield shift by 145.9 ppm (singlet) with respect to the external reference CCl3F [2]. The hydrolysis of the oxide tetrafluoride has been studied in a 20 wt% solution of MoOF4 in CH 3CN by adding a 20 wt% solution of H20 in CH 3CN. The intermediate formation of oxohy droxo tri- and difluoro complexes has been detected by 19F NMR spectroscopy. The introduc tion of 1.7 wt% H20 leads to the formation of MoO(OH)F3 ·CH3CN, MoO(OHhF2·CH3CN, and small amounts of M020 2Fg and HF. By increasing the H20 concentration to 3.5 wt% a partial replacement of CH 3CN by H20 occurs yielding MoO(OH)F3H20 and MoO(OH)2F2H20. With the con\ent of H20 in the solution of about 7 wt% a sharp increase in the concentration of HF (about 50% of the total fluorine content) takes place and the main Mo containing species is MoO(OH)F3H20. Also small amounts of MoO(OH)F3 • CH3CN, MoO(OHhF2H20, and MoO(OH)F2(H20)~ form [6]. KrF2 reacts with MoOF4 at different proportions in S02ClF solution to give adducts KrF2·nMoOF4 with n=1 to 3 (see p. 238) [7]. The reaction between MoOF4 and RbF in liquid S02 at - 30 to - 20°C (N2 atmosphere) yields crystalline Rb[M020 2F9] as the only product at any ratio of the reactants [8]. With WOF;- in CH 3CN a mixed dimeric anion with a bridging fluorine atom, OF4MoFWF40-, forms in the solution [9]. Gmelin Handbook Mo Suppl. Vol. B 5 206 MoLybdenum Oxide Fluorides In the interaction of MoOF4 in aeetonitriLe with various unidentate and bidentate oxygen eontaining Ligands repLaeement of fLuorine in cis position to the muLtipLy bonded 0 atom is deteeted by 19F NMR and a range of substitution and substitution-with-addition produets has been obtained: reaetant produets in soLution Ref. ethanoL MoOF3(OC2Hs)' CH 3CN, MoOF3(OC2Hs)' C2HsOH [4, 10] ethyLene gLyeoL MoOF3(OCH2CH20H), trans-MoOF2(OCH2CH 2OH)2 [10] acetylacetone MoOF3(CH2COCHCOCH3), M020 2F;; [4,5,10] phenoL MoOF3(OCsHs)' CH 3CN [10] In the noneoordinating soLvents CH2CL2 and toLuene, MoOF4 reaets with triphenylphosphine oxide (Ph3 PO) at moLe ratios 1:1 and 0.5: 1 to form the moLar oetahedraL eompLexes MoOF40PPh3 and Mo02F2(OPPh3h. With exeess MoOF4 aLong with MoOF40PPh3 the dimerie fLuorine bridged speeies M020 2FaOPPh3 and M020 2F;; oeeur. The addition of either Ph3PO or a soLvent with donor properties (CH3CN) eauses the deeomposition of the dimerie eompound and the formation of monomerie eompLexes [11]. References: [1] Paine, R. T.; Quarterman, L. A. (Inorg. NueL. Chem. SuppL. H. H. Hyman Mem. VoL. 1976 85/6). [2] Bougon, R.; Bui Huy, T.; Charpin, P. (Inorg. Chem. 14 [1975]1822/30). [3] Atherton, M. J.; HoLLoway, J. H. (Chem. Commun. 1978254/5). [4] BusLaev, Yu. A.; Kokunov, Yu. V.; Boehkareva, V. A.; Shustorovieh, E. M. (DokL. Akad. Nauk SSSR 201 [1971]355/8; DokL. Chem. Proe. Aead. Sei. USSR 196/201 [1971]925/8). [5] BusLaev, Yu. A.; Kokunov, Yu. V.; Boehkareva, V. A.; Shustorovieh, E. M. (Zh. Strukt. Khim. 13 [1972] 526/8; J. Struet. Chem. [USSR]13 [1972] 491/2). [6] lI'in, E. G.; GoLovanov, B. V.; Ignatov, M. E.; Butskii, V. D.; BusLaev, Yu. A. (DokL. Akad. Nauk SSSR 276 [1984]612/5; DokL. Chem. Proe. Aead. Sei. USSR 274/279 [1984]187/90). [7] HoLLoway, J. H.; SehrobiLgen, G. J. (Inorg. Chem. 20 [1981] 3363/8). [8] Beuter, A.; Sawodny, W. (Angew. Chem. 84 [1972] 1099/100). [9] BusLaev, Yu. A.; Kokunov, Yu. V.; Boehkareva, V. A. (Zh. Neorgan. Khim. 17 [1972]3377/8; Russ. J. Inorg. Chem. 17 [1972]1774/5). [10] BusLaev, Yu. A.; Kokunov, Yu. V.; Boehkareva, V. A.; Shustorovieh, E. M. (Zh. Neorgan. Khim. 17 [1972] 3184/90; Russ. J. Inorg. Chem. 17 [1972]1675/8). [11] Ignatov, M. E.; lI'in, E, G.; GoLovanov, B. V.; Butskii, V. D.; BusLaev, Yu. A. (DokL. Akad. Nauk SSSR 277 [1984]375/8; DokL. Chem. Proe. Aead. Sei. USSR 274/279 [1984]236/9). 2.4.1.8 The MoFs-Mo03-HF-H20 System SoLutions of MoFs in aqueous HF are eharaeterized by hydrolysis, see p. 170. The soLubiLi ties in the MoFs-HF-H20 system at oac were studied by the isotherm aL soLubiLity method. The system is regarded as a ternary reeiproeaL system with repLaeement of the fLuorine in MoFs by oxygen: MoFs + (3 + n)H20 ~ Mo03 + 6HF + n H20, see Fig. 51. The foLLowing eompounds have been identified: Gmelin Handbook Mo Suppl. Vol. B 5 207 compound range of concentration MoOF4 ·2.5H20 61.8 to 34.7 wt% HF Mo02F2 ·2H20 34.7 to 17.2 wt% HF Mo03 ·H20 17.2 to 0 wt% HF At HF concentrations cLose to 100% the MoFs readiLy forms supersaturated soLutions. 0.8 .MoO)· HzO MoOzFz· ZHzO • o E Fig.51. Phase diagram of the MoFs-Mo03-HF-HP system at O°C. 0.4 0.6 0.8 mole troctions NikoLaev, N. S.; OpaLovskii, A. A. (Zh. Neorgan. Khim. 4 [1959]1174/83; Russ. J. Inorg. Chem. 4 [1959]532/6); NikoLaev, N. S. (lzv. Sibirsk. Otd. Akad. NaukSSSR Sero Khim. Nauk 1968 No. 2, pp. 3/12, 10; C.A. 69 [1968] No. 80820). 2.4.1.9 MoOF4' n H20, n = 2, 2.5 White crystaLs of MoOF4 ·2H20, formuLated as acid H2Mo02F4 ·H20, form by dissoLving Mo03 in 40% aqueous HF and then precipitating with acetone. The precipitate is washed with acetone and dried over concentrated suLfuric acid and caustic soda to constant weight. The dihydrate is highLy soLubLe in H20 and in ethanoL but onLy sLightLy soLubLe in acetone [1]. MoOF4 ·2.5H20, formuLated as H2Mo02F4 ·1.5H20, forms in the MoFs-Mo03-HF-H20 sys tem, see above. It is extremeLy hygroseopie and rapidLy becomes Liquid in air, hydrolysis taking pLace with the formation of "moLybdic acid". Upon heating at 45°C the substance fuses compLeteLy in its own water of crystaLLization without change of composition. At 160°C, Mo03 forms as a yeLLow powder [2]. References: [1] Chakravorti, M. C.; Pandit, S. C. (Indian J. Chem. 9 [1971] 1306/7). [2] NikoLaev, N. S.; OpaLovskii, A. A. (Zh. Neorgan. Khim. 4 [1959]1174/83; Russ. J. Inorg. Chem. 4 [1959] 532/6). Gmelin Handbook Mo SuppL VoL 85 208 MoLybdenum Oxide Fluorides 2.4.1.10 MoO(OH)F3 • H20 A compound of this composition forms during the hydrolysis of MoOF4 in CH 3CN on addition of more than 3.5 wt% H20, see p. 205. The 19F NMR spectrum shows downfieLd shifts of ö(F1) = - 42.5 and ö(F2) =- 52.2 ppm and a spin-spin coupLing constant J(F1F 2) =104 Hz for the cis-reLated fLuorine nucLei. lI'in, E. G.; GoLovanov, B. V.; Ignatov, M. E.; Butskii, V. D.; BusLaev, Yu. A. (Dokl. Akad. Nauk SSSR 276 [1984] 612/5; Dokl. Chem. Proc. Acad. Sci. USSR 274/279 [1984]187/90). 2.4.1.11 Mo02F2 OLder data are given in "MoLybdän", 1935, p.152. 2.4.1.11.1 Preparation. Formation The high-temperature fLuorination of Mo02CL2with HF, which has aLready been described in 1907 (see "MoLybdän", 1935, p. 152), proved to be a reLiabLe method to prepare Mo02F2. The reaction is carried out at 280 to 300°C in a nickeL reactor. After 3 to 4 h voLatiLe products are removed at O°C and Mo02F2 remains as a purpLe gLassy [1] or paLe LiLac solid [2]. ALso this product and the expected voLume of Xe and CL2 are obtained when stoichiometric quantities of Mo02CL2 and XeF2 are mixed at -196°C and then warmed to O°C in anhydrous HF [1,2]. Pure Mo02F2 forms by heating a mixture of Mo03 and MoOF4 at 180 to 200°C. The synthesis is accompLished in evacuated and seaLed ampuLes with the voLatiLe component being in sLight excess, which is distiLLed off under vacuum when the reaction is compLeted [3]. The reaction between Mo03 and IFs yieLding Mo02F2·2IFs and I02F [4, 5] can be used to prepare the Mo02F2 [6]. SimiLarLy, Mo03 and SeF4 give Mo02F2·SeF4 and SeOF2 [5]. When LiF is heated with Mo03, e.g. at moLe ratio 3 :1, to temperatures in the range 730 to 830°C under anhydrous conditions, Mo02F2 forms in addition to Li2Mo04 [7]. For preparation, LiF and Mo03 are mixed at a moLe ratio> 5 :1, covered with an additionaL LiF Layer in a nickeL boat and pretreated by heating in air at 250 to 300°C (12 h). VoLatiLe impurities are removed by evacuating the stainLess steeL ceLI. Then the synthesis is carried out in an atmosphere of argon or oxygen at temperatures above 500°C [8]. Formation of Mo02F2 takes pLace when moLybdenum metaL reacts with N02F at room temperature [9, 10]. The compound occurs as an oxidation product of MoF3 after exposure to air for severaL years and of MoFs after exposure to air for 30 min [11]. It forms as a by-product in the reaction between Mo03 and NF3 at 430°C [12]. and during the decomposition of MoF4(OTeFsb by spLitting off TeFs [13]. Mo02F2 was mass spectrometricaLly detected as the onLy Mo-containing moLecuLe in the vapor generated by heating Mo02 with CrF2 in a tantaLum Knudsen ceLl at 645 to 748°C or by heating Mo02 with MnF2 in a moLybdenum ceLl at -900°C [14]. References: [1] Atherton, M. J.; Burgess, J.; HoLloway, J. H.; Morton, N. (J. FLuorine Chem. 11 [1978] 215/24, 217). [2] Atherton, M. J.; HoLloway, J. H. (Chem. Commun. 1978254/5). [3] NikoLaev, A. V.; OpaLovsky [OpaLovskii], A. A.; Fedorov, V. E. (Therm. Anal. Proc. 2nd Intern. Cont., Worcester, Mass., 1968 [1969], Vol. 2, pp. 793/810, 799; C.A. 73 [1970] No. 94206). [4] AynsLey, E. E.; NichoLs, R.; Robinson, P. L. (J. Chem. Soc. 1953623/6). Gmelin Handbook Mo Suppl. Vol. B 5 209 [5] Bartlett, N.; Robinson, P. L. (J. Chem. Soc. 1961 3549/50). [6] Beattie, I. R.; Livingston, K. M. S.; Reynolds, D. J.; Ozin, G. A. (J. Chem. Soc. A 1970 1210/6, 1215). [7] Schmitz-Dumont, 0.; Heckmann, I. (Z. Anorg. Allgern. Chem. 267 [1951/52] 277/92, 282, 287,291). [8] Ward, B. G.; Stafford, F. E. (Inorg. Chem. 7 [1968] 2569/73). [9] Aynsley, E. E.; Hetherington, G.; Robinson, P. L. (J. Chem. Soc. 1954 1119/24). [10] Hetherington, G.; Robinson, P. L. (Chem. Soc. [London] Spec. Pub!. No. 10 [1957]23/32, 27). [11] Redman, J. D.; Strehlow, R. A. (ORNL-4229 [1968] 37/9; N.S.A. 22 [1968] No. 25374). [12] Glemser, 0.; Wegener, J.; Mews, R. (Chem. Ber. 100 [1967] 2474/83, 2476). [13] Schröder, K.; Sladky, F. (Z. Anorg. Allgern. Chem. 477 [1981] 95/100, 97). [14] 2mbov, K. F.; Uy, 0. M.; Margrave, J. L. (J. Phys. Chem. 73 [1969] 3008/11). 2.4.1.11.2 Physical Properties Solid Mo02F2 neither melts nor sublimes in vacuum up to 310°C [1]. However, earlier a sublimation temperature of 120°C has been given [9], see also [10]. Forthe conditions used to produce Mo02F2 vapor above 500°C, see the IR study [2]. From mass-spectrometric studies in the molybdenum trifluoride-molybdenum oxide fluoride system the temperature dependence of the vapor pressure has been obtained between 731 and 832 K; P =1.6 x10-4 Torr at 751 K [10]. The enthalpy and entropy of sublimation at 298 K have been estimated at 104 kJ/mol and 204 J. mol-j • K-1, respectively [3, p. 367]. The entropy and heat capacity of gaseous Mo02F2 have been estimated at 318 and 79 J. mol-I. K-l, respectively [3, p. 364]. The enthalpy of atomization LlH 200.at of gaseous Mo02F2 was determined as 582 ±15 kcalJ mol from the reaction 0.4 TaF5(g)+Mo02(S)~Mo02F2(g)+0.4Ta(s) studied mass spectro metrically at 645 to 748°C using Mo02 plus CrF2 mixtures in a tantalum Knudsen cell [4]. The LlH2sB.at value of [4] corresponds to an enthalpy of formation LlHf.298 (Mo02F2, g) = -1121 kJ/mol (-268 kcalJmol) implying LlHf.298 (Mo02F2,s) =-1200 kJ/mol [5]. The less nega tive value -1089 kJ/mol was found by solution calorimetry using aqueous NaOH. (The term "glassy" used to characterize part of the Mo02F2 sampies studied seems to refer to the appearance of the solid obtained rather than to imply an amorphous solid) [5]. Applying heuristic rules and using thermodynamic data on Mo03 and MoFs, the value LlHf.298 (MoO.F2,s)=-281±5kcalJmol (-1176±21 kJ/mol) has been estimated [6]. For gaseous Mo02F2, the value -1018 kJ/mol is given in [7]. Solid Mo02F2 is described as pale liIac [1]; purpLe, "glassy" Mo02F2 was studied in [5]. The IR spectrum (400 to 4000 cm-1) of the vapor studied above 500°C shows bands at 1009 and 987 cm-1 assigned to Mo=O vibrations and bands at 710 and 692 cm-1 assigned to Mo-F vibrations [2]. SoLid Mo02F2 shows IR absorption bands at 1007 (w, sh) and 993(s) cm-1. These features have the same shape as the band envelope of the corresponding gas phase absorp tion bands (reported by [2]). A strong broad band at 835 cm-1 is assigned to stretching vibrations involving Mo···O-Mo bridges. Bands at 695 (w) and 670 (s) cm-1 are attributed to terminaL Mo-F stretches. Bands at 587 (s) and 522 (w,sh) cm-1 are assigned to stretches of Mo··· F-Mo bridges [1]. Raman spectra of crystalline (?) and amorphous (?) Mo02F2 designat ed in the paper [8] as soLid and glassy, respectively, show the following shifts (in cm-1). For "solid" Mo02F2: 781 (m), 559 (s), 471 (m), 368 (vs), 267 (s), and 182 (m) were found; for "glassy" Mo02F2: 805 (w, vbr), 521 (vw, sh), 481 (s, vbr), and 379 (m, br) are given. If the band at 781 cm-1 is cjue to an Qxygen bridge, the Raman data wouLd support the presence of both bridging oxygen and bridging f1uorine atoms [8]. Gmelin Handbook Mo Suppl. Vol. B 5 14 210 Molybdenum Oxide Fluorides References: [1) Atherton, M. J.; Holloway, J. H. (Chem. Commun. 1978254/5). [2) Ward, B. G.; Staftord, F. E. (Inorg. Chem. 7 [1968) 2569/73). [3) Dittmer, G.; Niemann, U. (Mater. Res. Bull. 18 [1983) 355/69). [4) 2mbov, K. F.; Uy, 0. M.; Margrave, J. L. (J. Phys. Chem. 73 [1969)3008/11). [5) Atherton, M. J.; Burgess, J.; Holloway, J. H.; Morton, N. (J. Fluorine Chem. 11 [1978) 215/24). [6) Rakov, E. G.; Marinina, L. K.; Sudarikov, B. N.; Koshechko, L. G.; Fedorov, G. G. (Tr. Mosk. Khim. Tekhnol. Inst. No. 65 [1970) 28/30; C.A. 76 [1972) No. 104691). [7) Woolf, A. A. (Advan. Inorg. Chem. Radiochem. 24 [1981)1/55, 45). [8) Beattie, I. R.; Livingston, K. M. S.; Reynolds, D. J.; Ozin, G. A. (J. Chem. Soc. A 1970 1210/6, 1213). [9) Glemser, 0.; Wegener, J.; Mews, R. (Chem. Ber. 100 [1967) 2474/83, 2476). [10) Alikhanyan, A. S.; Steblevskii, A. V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978) 2549/52; Russ. J. Inorg. Chem. 23 [1978)1412/3). 2.4.1.11.3 Chemical Reactions. Solubility. Solutions For the decomposition according to 2 Mo02F2(s) ~ MoOF4(s) + Mo03(s), ~H~8 = 27 kJ/mol Mo02F2 and for 3 Mo02F2(s) ~ MoFs(l) + 2 Mo03(s), ~H~8 = 64 kJ/mol Mo02F2 have been esti mated [1). The individual mass spectrum of Mo02F2 at 751 K and 70 V electron impact has been calculated from mass-spectrometric measurements in the molybdenum trifluoride-molybde num oxide fluoride system as Mo+ (37), MoO+ (14), MoF+ (7), MoOF+ (30), MoFt (17), MoOFt (24), MoOt (9), Mo02F+ (78), Mo02Ft (100) (relative abundances in parentheses) [2). In addition to these main components M020 3 Ft appears in the mass spectrum, suggesting that Mo02F2 may be polymeric [3). For M002F2(g)+2F2(g)~MoFs(g)+02(g), ~H~=-106 kcaUmol has been calculated [4). Equimolar quantities of Mo02F2 and XeF2 in anhydrous HF give MoOF4 , with excess XeF2 the MoOF4 ·XeF2 adduct forms [3). The vapor phase over a mixture of MoF3 and Mo02F2 at 751 K contains only MoOF3 along with Mo02F2, but at 823 K also appreciable quantities of MoF3, MoF4, and MoFs were detected mass spectrometrically [2). For the reaction between Mo02F2 and MoF4 , see p. 92. From calorimetric measurements the enthalpy of hydrolysis in 1.0 M NaOH, ~H = -231±4kJ/mol (corresponding to M002F2+40W~MoO~-+2F-+2HP) [1). In aqueous solutions, Mo02F2 forms complexes with HF, namely HMo02F3 at mole ratios HF/Mo02F2 0.1 to 1.0 and H2Mo02F4 at mole ratios 1 to 10 [5) also cf. [6,7) and the section dealing with the corresponding ions, p.222ft. The reaction of Mo02F2 with a 40% H20 2 solution yields the peroxo species MOO(02)2FH20- and HF at mole ratio 1:1 [8), see also p. 236. Mo02F2 is soluble in S02ClF and slightly soluble in HF, but does not dissolve in CH 3CN, CHCl3, ClF2CCCl2F, and propylene carbonate [3). Saturated, 40%, and 20% aqueous Mo02F2 solutions have been studied by 19F NMR which indicates that intramolecular fluorine exchange occurs. Upon addition of HF, the M002F~ anion forms [6). Solutions of Mo02F2 in HF and in S02ClFplusHF mixtures show a broad singlet in the 19F NMR shifted (presumably downfield) by 131.5 ppm with respect to CCl3F [3). Gmelin Handbook Mo Suppl. Vol. B 5 211 References: [1] Atherton, M. J.; Burgess, J.; Holloway, J. H.; Morton, N. (J. FLuorine Chem. 11 [1978]215/24, 220). [2] ALikhanyan, A. S.; Steblevskii, A. V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khim. 23 [1978] 2549/52; Russ. J. Inorg. Chem. 23 [1978]1412/3). [3] Atherton, M. J.; Holloway, J. H. (Chem. Commun. 1978254/5). [4] Rakov, E. G.; Marinina, L. K.; Sudarikov, B. N.; Koshechko, L. G.; Fedorov, G. G. (Tr. Mosk. Khim. Tekhnol. Inst. No. 65 [1970] 28/30; C.A. 76 [1972] No. 104691). [5] Parpiev, N. A.; Maslennikov, I. A.; Abdullaeva, Kh. S. (Uzbek. Khim. Zh. 17 No. 6 [1973]3/5; C.A. 80 [1974] No. 137605). [6] Buslaev, Yu. A.; Shcherbakov, V. A. (Zh. Strukt. Khim. 7 [1966] 345/50; J. Struct. Chem. [USSR] 7 [1966] 332/6). [7] Maslennikov, I. A.; Parpiev, N. A. (Gidromet. Tsvet. Redk. Metal. 1971156/61; C.A. 76 [1972] No. 90849). [8] Buslaev, Yu. A.; Petrosyants, S. P.; Tarasov, V. P. (Zh. Strukt. Khim. 11 [1970] 616/22; J. Struct. Chem. [USSR]11 [1970] 574/9). 2.4.1.12 Mo02F2 • 2 H20 This hydrate which has also been formulated as H2Mo03F2 • H20 [1,2] and MoO(OHhF2 " H20 [3] forms a solid phase in the MoFe-Mo03-HF-H20 system, see p.206. , For preparation, a saturated solution of Mo03 in boiLing aqueous HF is cooled to room tem perature and the crystalline precipitate washed with ethanol and dried at reduced pressure at 50 to 60°C [2]. The formation of this compound in solutions of Mo03 in 40% HF has been estab lished by NMR and chemical analysis [4]. Mo02F2 ·2H20 forms by the hydrolysis of MoOF4 in CH3CN on addition of water at H20 concentrations in the solution of above 3.5 wt% (see p. 205) [3]. 19F NMR of the aqueous HF solution containing Mo02F2 ·2H20 shows a singlet shifted upfield by Iö I= 493 ppm with respect to F2. This indicates that the fluorine atoms are in trans position with respect to another. The molecule is formulated as cis-dioxo-cis-diaquo species [4]. 19F NMR yields a downfield shift öC 9F) of 134.6 ppm (with respect to HF) for the species formulated as cis-MoO(OHhF2(H 20) [3]. The IR spectrum of the compound is plotted for 400 to 4000 cm-1 in the paper. The broad absorption between - 555 and - 595 cm-1 is assigned to Mo-F vibrations; bands near 932 and 977 cm-1 are tentatively assigned to symmetric and antisymmetric Mo02 stretches; the band at -1640 cm-1 is assigned to deformation vibrations of H20. Further bands: -1415 (NHt impuri ty?), -1898, and -2600 to 3600 cm-1 [5]. Mo02F2 ·2 HP forms colorless crystals that are stable in a vacuum but decompose slowly in air, becoming first yellow and then greenish yellow. The thermal analysis shows three endo thermal effects: at 290°C removal of 1 mol H20 and 0.5 mol HF, at 380°C formation of H3M040 13F, and at 555°C formation of pure Mo03. The intermediate products occurring during the thermal decomposition were assumed to be fluoro substituted isopoly acids. The Mo02F2 ·2H20 has a considerable solubiLity in water which increases from 3.09 at O°C to 3.90 moVL at 90°C. The final heat of solution, - 0.4805 kcaVmol, was calculated using Schröder's equation [2]. The water molecules in the coordination sphere of Mo02F2 • 2 H20 can be substituted by numerous aliphatic alcohols (L) containing 1 to 5 C atoms forming Mo02F2 • H20· Land Mo02F2 • 2 L. This is also the case with acetone, acetonitrile, and dimethyl sulfoxide. With pyridine and formamide, species form containing three fluorine atoms while with oxaLic acid and acetylacetone those with one fluorine atom form [4]. Gmelin Handbook Mo Suppl. Vol. B 5 14· 212 MoLybdenurn Oxide Fluorides References: [1] NikoLaev, N.'S.; OpaLovskii, A A. (Zh. Neorgan. Khirn. 4 [1959]1174/83; Russ. J. Inorg. Chern. 4 [1959] 532/6). [2] NikoLaev, N. S.; OpaLovskii, A. A. (DokL. Akad. Nauk SSSR 124 [1959]830/3; Proe. Aead. Sei. USSR Chern. Seet. 124/129 [1959] 85/8). [3] lL'in, E. G.; GoLovanov, B. V.; Ignatov, M. E.; Butskii, V. D.; BusLaev, Yu. A. (DokL. Akad. Nauk SSSR 276 [1984] 612/5; DokL. Chern. Proe. Aead. Sei. USSR 274/279 [1984] 187/90). [4] BusLaev, Yu. A.; Petrosyants, S. P. (Zh. Neorgan. Khirn. 16 [1971]1330/6; Russ. J. Inorg. Chern. 16 [1971] 702/6). [5] Kharitonov, Yu. Ya.; BusLaev, Yu. A; Kuznetsova, A A. (Zh. Neorgan. Khirn. 11 [1966]821/6; Russ. J. Inorg. Chern. 11 [1966] 445/8). 2.4.1.13 H3M040 13F This eornpound was identified as an intermediate produet of the thermaL deeornposition of MoOaF2·2H20 at 380°C, see above. NikoLaev, N. S.; OpaLovskii, A. A. (DokL. Akad. Nauk SSSR 124 [1959]830/3; Proe. Aead. Sei. USSR Chern. Seet. 124/129 [1959] 85/8). 2.4.2 Molybdenum Oxide Fluoride Ions 2.4.2.1 The Cations MoOF~ (rn=1 to 4), Mo02F~(n=1,2}, and M020 3Ft The ions MoOF~ with rn =1 to 3 and M002F~with n =1 or 2 oeeur in appreeiabLe arnounts in the rnass speetra of MoOF3, MoOF4, and Mo02F2, see pp. 192,202, and 210, respeetiveLy. OnLy traees of the MoOFt speeies eouLd be deteeted in the rnass speetrurn of MoOF4 • Mo02F+ and Mo02Ft oeeur aLso in the rnass speetrurn of NO[Mo02F3] [1]. The dirnerie speeies M020 3 Ft appears in the rnass speetrurn of Mo02F2 indieating the existenee of poLymerie rnoleeuLar preeursors, see p. 210. The following appearanee potentiaLs (AP) have been rneasured in the saturated vapor of the rnoLybdenurn trifluoride-rnolybdenurn oxide fluoride system at 751 K [2] and in the vapor pro dueed by reaeting Mo02+CrF2 in a tantalum Knudsen eell at 645 to 748°C orwith Mo02+ MnF2 in a rnolybdenurn eell at 900°C [3]: ion ...... MoOF+ MoOF+ MoOF+ MoOFt MoOFt AP in eV ...... 23.0±0.58 ) 23.0±1.0b) 16.0±0.5 17.0±1.0 11.0±0.5 Ref...... [3] [3] [2] [2] [2] ion ...... Mo02F+ Mo02F+ Mo02Ft Mo02Ft AP in eV ...... 15.0±0.58 ) 15 ± 1b) 13.0±0.38 ) 13.0±0.5b) Ref...... [3] [3] [3] [3] References: [1] Glernser, 0.; Wegener, J.; Mews, R. (Chern. Ber. 100 [1967] 2474/83, 2476). [2] Alikhanyan, A. S.; Steblevskii, A. V.; Pervov, V. S.; Butskii, V. D.; Gorgoraki, V. I. (Zh. Neorgan. Khirn. 23 [1978] 2549/52; Russ. J. Inorg. Chern. 23 [1978] 1412/3). [3] Zrnbov, K. F.; Uy, 0. M.; Margrave, J. L. (J. Phys. Chern. 73 [1969] 3008/11). Gmelin Handbook Mo Suppl. Vol. B 5 MoLybdenum Oxide FLuoride Ions 213 2.4.2.2 Oxofluoromolybdate Anions OLder data are given in "MoLybdän", 1935, pp. 151/3. Survey. MoLybdenum(V) and moLybdenum(VI) form a variety of mono-, di-, and poLymerie oxofLuoromoLybdate anions which have been isoLated as soLid compounds with inorganic and organic cations. With moLybdenum(IV) onLy the trinucLear cLuster M030 4F1j- has recentLy been detected. The species containing OH and H20 are aLso described in this section. The structures of the oxofLuoromoLybdate anions are buiLt up from octahedra of oxygen and fLuorine atoms in which the moLybdenum atoms occupy the centers. In the dimeric and poLymerie anions these octahedra are connected by shared corners or shared edges with oxygen or fLuorine as bridging atoms. In M020 6 Pa-, which has the highest Mo: F ratio of dimeric species so far known, two octahedra share a face. These structuraL variations and the presence of two different Ligands that are abLe to repLace each other cause the great variety in the structures and compositions of these species. 2.4.2.2.1 Oxofluoromolybdate(lV) M0304F~-. The existence of the oxofLuoro species M030 4F1j- with moLybdenum in oxidation state +4 has been demonstrated by the isoLation of crystaLLine (NH 4)5[M030 4Fg]· NH4F· H20 from mineraL acid soLution. A soLution containing the oxofluoromoLybdate(lV) ion can be produced by adsorption of MoOCL~- + MoCm- on an ion exchange coLumn and eLution with aqueous HF. From the red soLution red-bLack crystaLs of the ammonium saLt are precipitated by adding excess NH4F. The crystaL structure anaLysis shows the anion to consist of a trinucLear cluster in wh ich octahedraL Mo is bonded to 3 bridging °and 3 F atoms, see Fig. 52. The bond distances are Mo--Mo = 2.505, Mo--F = 2.034, Mo--O = 2.032 and 1.920 Ä. The existence of the centraL M030 4 cLuster unit is aLso accepted for the species in aqueous HF. The visibLe spectrum of the M030 4F1i- cLuster anion is characterized by an absorption band which occurs at 525 nm in the refLection spectrum of solid (NH4)5[M030 4Fg]· NH4F· Hp. In soLution a doubLet occurs with peaks near 518 and 535 nm. Exchange of F- by H20 giving M0304Fg_n(H20)~-n)- is assumed for the aqueous soLution since the ratio of the intensities of the 518 and 535 nm bands change with time after dissoLution of the soLid compound (no change was noted in the positions of the absorption peaks). Fig.52. Structure of the M030 4F1j- anion in (NH4)5[M030 4F5]· NH4F· H20. MüLLer, A.; Ruck, A.; Dartmann, M.; Reinsch-VogeLL, U. (Angew. Chem. 93 [1981] 493; Angew. Chem. Intern. Ed. Eng!. 20 [1981] 483). Gmelin Handbook Mo Suppl. Vol. B 5 214 MoLybdenum Oxide FLuoride Ions 2.4.2.2.2 Oxofluoromolybdates(V) The monomeric species MoOF4 and MoOF~-, and the dimeric species M0204F~-, M020 4Ps-, M020 4F3-, and M020 2Pg- are known. With the exception of MoOF4, they aLL can be isoLated as crystaLLine saLts. MoOF4 and MoOF~- can be incorporated in host crystaLs. In addition to the anhydrous oxofLuoromoLybdates the anions Mo(OH}F~- and MOP4F4(HPW have been investigated in their solid saLts. MoOF". SingLe crystaLs of (NH4hSbFs containing MoOF4 can be made by dissoLving (NH4hSbFs and NH4F in water in moLe proportion of 1: 1, adding a soLution of ammonium moLybdate in hydrofLuoric acid reduced with metallic tin, and aLLowing the soLution to eva po rate sLowLy [1]. In addition, the MoOF4 species has been observed in the mass spectrum of a mixture of MoF3 with a minor amount of KBe2FS in the presence of smaLL amounts of oxygen [2]. C4v symmetry, estimated distances Mo-O and Mo-F of 1.61 and 1.88 A, respectiveLy, and an 0-Mo-F angLe of 105.2° were assumed in SCF-MS-Xa (seLf-consistent fieLd-muLtipLe scattering SLater exchange) caLcuLations. The contribution of d eLectrons from Mo to the Mo-O bond is caLcuLated as - 25% for the 3t and - 32% for the (J bond. The charge (in eLementary charges) is distributed as foLLows: + 1.639 on Mo, - 0.419 on 0, and - 0.556 e on F. The eLectron popuLation of the Mo orbitaLs is 1.943, 5.522, 3.850, 0.329, and 0.719 e on 3s, 3p, 3d, 4s, and 4p, respectiveLy [3]. EPR data have been evaLuated by SCF-MS-Xa oaLcuLations in terms of moLecuLar orbitaL coefficients [1]. The X-band EPR of MoOF4 ions was measured at room temperature on (NH4hSbFs crystaLs doped with MoOF4 ions [1]. The parameters for the spin-HamiLtonian are gll = 1.895 (exp. [1]) and 1.898 (caLc. [3]), g.L = 1.925 (exp. [1]) and 1.927 (caLc. [3]). The moLybdenum hyperfine interaction tensor has components (in 10-4 cm-1) of All = 85.38 (exp. [1],~95.5 G) or 81.18 (caLc. [3]) and of A.L=38.36 (caLc. [3]). The 19F hyperfine Lines yieLded AxC9F)=-15G and AyC 9F) = + 55 G [1]. The spin-orbit coupLing constant ~~ = 895 cm-1 and the vaLue MoOFg-. CrystaLLine saLts containing the MoOF~- anion have been weLL known for a Long time, see "MoLybdän", 1935, p. 151. A Large number of saLts of the type MMMoOFs] with inorganic and aLso with organic cations (M) can be isolated from aqueous soLutions. The favored preparative method consists in crystaLLizing soLutions of MoO(OHh and the metaL fluorides or the organic bases in 40% aqueous HF [4].lnstead of MoO(OHla, MoCLs can be used as starting materiaL [5] or eLse molybdates(VI) are reduced in 35 or 40% HF by metals (Zn or Sn) [6] or hypophosphoric acid [4]. K2[MoOFs]· H20 can be prepared from a soLution of Mo02 in aqueous HF by precipitation with KHF2. With excess KHF2, turquoise bLue K2[MoOF2]· KHF2 precipitates [18]. DetaiLs of preparation and additionaL methods will be described in a Later "MoLybdenum" voLume deaLing with the corresponding saLts. The oxidation state of moLybde num in Mk[MoOFs] compounds was determined as ca. + 5 by chemicaL and magnetic methods [4]. Some Movand F may be partiaLLy substituted by MOVI and 0, respectiveLy, the totaL anionic charge remaining constant. For (NH4MMoOFs], e.g., 7 to 10% of the totaL Mo conte nt is in the + 6 oxidation state [5]. MoOF~- anions can be incorporated into various host crystaLs. Doped (NH4hGeFs singLe crystaLs can be made by sLow evaporation of a saturated soLution of (NH4hGeFs in 38 wt% GmeLin Handbook Mo Suppl. Vol. B 5 OxofluoromoLybdates(V) 215 hydrofluoric acid to which an MoOFt soLution is added [7]. In the presence of the moLybdenyL ion and a Large excess of hydrofluoric acid, doped K2SnFs' H20 crystaLs form by sLow evaporation of the soLvent [8]. CrystaLs of K2NbOFs' KHF2 containing 0.5 wt% K2MoOFs can be made by adding 2: 1 proportions of KF and MoCLs in 48 wt% HF to K2NbOFs ' KHF2 dissoLved aLso in HF [9]. CrystaLLographic studies of K2[MoOFs]' H20 show that the MoOF~- species beLongs to the Cs symmetry group, but this Low symmetry is probabLy due to the influence of the hydrate water. The Mo atom is surrounded by 4 F atoms at an average distance of 1.88 Aand the fifth F at 2.03 A. The Mo--O distance is 1.66 A [10, 11]. In (NH4h[MoOFs] the equatoriaL Mo-F distances are 1.952(13) and 1.940(14) A; the axiaL one is 1.994(6) A. The Mo--O distance is 1.705(8) A [5]. In soLution, the probabLe symmetry group is C4v [11]. CaLcuLated spectra from MoOF~- best agree with measured opticaL spectra from K2[MoOFs]·H20 when atomic distances cLose to those of [11] are used; aLso see [3]. The caLcuLated contribution to Mo--O a and Jt bonds by d eLectrons are - 31.5 and - 22.5% according to seLf-consistent fieLd-muLtipLe scattering SLater exchange (SCF-MS-Xa) caLcuLa tions. The charge distribution in the ion is + 1.66 e on Mo, - 0.489 e on 0, - 0.616 e on F (4 x), and - 0.708 e on the axiaL F. The eLectron distribution over the Mo orbitaLs was caLcuLated as 1.942, 5.525, 3.781, 0.314, and 0.778 e- on 3s, 3p, 3d, 4s, and 4p orbitaLs, respectiveLy [3]. Coefficients of the moLecuLar orbitaLs have been derived from the superhyperfine interac tions observed by EPR [9,12,13], see aLso the papers [3,14 to 16] which based their caLcuLa tions on the data of [9]. Spin densities on the fluorine orbitaLs have been caLcuLated in [9] and [17]. The spin orbit coupling constant ~o = 902 cm-1. For the radiaL distribution of the 4d eLectrons, the average < r-3>~~ = 4.89 a. u. [3]. Force constants have been derived from IR and Raman spectra of K2[MoOFs] and K2[MoOFs]' H20. VaLence force constants (in mdyn/A) are for MO---D 7.56 and for Mo--F 2.76 (obviousLy equatoriaL F) and 1.83 (axiaL F) [18]. For MO---D, earlier the vaLue - 8.4 was given in [11]. The light green soLutions of MoO(OH)s or K2MoOFs in 40% HF are paramagnetic (fleff =1.85 fls, spin-onLy vaLue for d1 :1.73 fls). (ObviousLy by poLymerization of the moLybdenyL ions) the soLutions turn brownish red on diLution and at HF concentrations ~2% they are diamagnetic, see the tabLe of the [HF] dependence of the magnetic suspectibiLity given in [19]. Q and X band EPR spectra have been recorded at 77 K on oriented MoOF~- ions which were doped into (NH4)2GeFS singLe crystaL hosts [7] (the use of KNbOFs' KHF2 hosts by [9] was criticized in [7]). The spectroscopic spLitting factors are gll =1.894 and g1. = 1.913 [7,12]; gll=1.874 and g1. =1.911 are given in [9]. Citing and sometimes sLightLy revising the super hyperfine coupling constants reported in [7] the foLLowing vaLues of A and a (in 10-4 cm-1) are given in [12]: AII =90.1, Al. =42.8 (hyperfine interaction); superhyperfine coupling constants (for F): ax = -19.7, Gmelin Handbook Mo Suppt. Vol. B 5 216 Molybdenum Oxide Fluoride Ions [22] or solutions at room temperature containing Mo enriched to 83.6% 95Mo or -96% 98Mo [13], see also [6]. IR and Raman spectra are reported for solid K2[MoOF5], K2[MoOF5]· H20, and K2[MoOF5]· KHF2. For K2[MoOF5], the Raman shifts (in cm-l) by 990 (vs) and 290 (w) are attributed to v(MO=Ü) and ö(Ü=Mo-F) vibrations of Al and E symmetry, respectively. The IR spectrum of K2[MoOF5] in the 200 to 4000 cm-l range is as follows [18]: v in cm-l ...... 995, 970(s,br) 590(sh) 530(vs) 445(sh) 282(s) 255(m) symmetry type .... Al Al Al type of vibration v(MO=Ü) v(MoF4) v(Mo-Fax) M2[MoOF5] salts are blue (M = NH4) [5, p. 201] or green (M = K, Rb, Cs) [4]. MoOF~- doped K2SnFs' H20 crystals are blue [8]. For green solutions in HF, see [19]. The optical absorbance of the MoOFg- ion was studied in - 20 M HF solution between 7000 and 27600 cm-l [23] (up to 30000 in [24]). The following extinction coefficients 10, band energies, and assignments to d-d transitions are given [23]: energy in cm-l (in eV) ... 8300 ± 150(1.03) 13250 ± 100(1.64) ~27600 (~3.42) Ein cm-l/(mol·L-l) ...... 0.4±0.1 9.9±0.1 >3 transition ...... 2E ~2B2 2Bl~2B2 2Al~2B2 According to a modified INDO-MO study (intermediate neglect of differential overlap-molecu lar orbital), the three lowest lying transitions in the optical spectrum are d-d transitions, the fourth transition is a charge-transfer transition. The following energies have been calculated [17] : energy in eV (in cm-l) .. 1.01(8147)a) 2.73(22020) 3.28(26456) 4.28(34522)b) assignment ...... 2E(dxy--->dxy.yz) 2A2(dxy--->dx>-y2) 2B2(dxy--->dz2) 2Al(Fn+On--->dxz.vz) a) Oscillator strength: 0.00023.- b) Charge-transfer transition. The attribution of the above experimental spectrum (- 20 M HF SOlution) to MoOF~- is corroborated by a study of K2[MoOF5]· H20/KCl pellets [23] (for a spectrum plotted between - 7000 and - 31000 cm-l , see [24]). The optical spectrum of MoOF~- ions doped into K2SnFs' H20 crystalline hosts was recorded at 77 K and is plotted for 400 nm ~ A ~ 1 !im. Band maxima are at 12300 and 13100 cm-l and at 21200 and 22000 cm-l (double peak structure with splitting ß "'" 800 cm-l). These transitions around 12700 and 21600 cm-l have been attributed to E(dxy--->dxy.yz) and E(dxy--->dx2_y2) transitions for which transition energies of 8890 cm-l (1.1 eV) and 34460 cm-l (4.27 eV), respectively, have been calculated [3]. The spectra in [8,23] are discussed in terms of charge-transfer transitions (for 13250 to 98000 cm-l) in [26]. Crystalline salts containing the MoOFg- anion are generally green in color. They are stable when dry but turn blue in the presence of moisture [4]. In acid solution, e.g. 30% aqueous HF, they dissociate into the anion MoOFg- and the cation [4, 25]. With decreasing HF concentra tion the anions undergo hydrolysis and ultimately, at - 2% HF, dimerise to give diamagnetic complexes similarly as observed with the corresponding oxochloro species [19]. The electrical conductivity of aqueous solutions containing the MoOFg- ion indicates that this ion at 30°C does not dissociate to any appreciable extent [4]. This was also indicated by the independence of the 19F NMR relaxation rate on the acidity of the solution (in aqueous HF, studied between 0 and 64°C). There is no or at most slow exchange of fluorine between the MoOF~- anion and the solution [25]. Gmelin Handbook Mo Suppl. Vol. B 5 Oxofluoromolybdates(V) 217 Mo(OH)F~-. This species occurs in the solid hydroxofluoromolybdates(V), Mk[Mo(OH)Fs] with M = K, Rb, Cs, TI, 1/2 N2Hs, and C10HlON (1-methylquinolinium). The parent compound of this series, N2H6[Mo(OH)Fs]' H20, can be obtained by reducing at water bath temperature a solution of Mo03 in 40% aqueous HF with hydrazine. The other salts are produced by reacting the corresponding fluorides with concentrated solutions of the hydrazinium salt in 20% aqueous HF. The formulation is based on complete elemental analysis, determination of the oxidation state of molybdenum, magnetic moment values (1.56 to 1.82 fls at 30°C), and IR spectral studies. The IR spectra show the characteristic v(O-H) band at 3250 to 3550 cm-1, while the Ö(H-O-H) band is absent. The very strong and intense band at 980 to 990 cm-1 is assigned to the deformation mode of the Mo-O-H group. Thus the alternative formulations MkH[MoOFs] or Mk[MoOFs]' HF were not favored. The solid compounds are green. They are stable when dry but turn blue in the presence of moisture. They dissolve in water to form green solutions which gradually change to light orange. The salts are soluble in dilute hydrofluoric acid [27]. M0204F~-, M0204F4(H20)~-, M020 4Fg-, M0204F~-, M020 2Pg-. The oxofluoromolybdate anions M0204F~-, M020 4Ps-, and M020 4F3- form when MoO(OHh is dissolved in dilute aqueous HF (e.g. 2%). Crystalline salts of these ions can be isolated by adding various cations (alkali, bipyridyl, and phenanthroline). The type of the salt separated depends on the nature and concentration of the cation [19]. The M0204F~- and M020 4F3- species can also be precipitated from solutions of MoCls in aqueous ethanol or tetrahydrofuran by adding aqueous solutions of fluorides [28,29]. Solid salts containing the M020 2Pg- anion can be obtained from 40% hydrofluoric acid solutions of Cs2[MoOCls] and of MoCls + NH4F. In these preparations approximately 10% of the total Mo content is in the + 6 oxidation state. The additional positive charge is balanced by replacing fluoro ligands by oxo ligands [5, 30]. X-ray diffraction studies of the crystalline (NH4)2[M0204F4(H20)2] indicate C2 symmetry for the anion with cis position of the terminal Mo=ü bonds. The anion contains the dioxo-di-fl-OXO dimolybdate(V) group, see Fig.53. Each Mo atom is situated in the center of a distorted octahedron and two octahedra are connected by sharing edges occupied by ° atoms. The four-membered ring, M020 2, is not planar. The Mo-Mo distance of 2.566(0) A and the magnetic, IR, and Raman spectroscopic data suggest the presence of a metal to metal bond. Other atomic distances: Mo-O(1) = 1.681 (2), Mo-O(2) = 1.938(2), Mo-O(3) = 2.281 (2), Mo-F(1) = 2.040(2), Mo-F(2) = 2.049(1) A. Angles: O(2}-Mo-O(2) = 93.3(1)", Mo-Q(2)-Mo = 82.8(1)"; for other distances and angles see paper [29]. The IR, Raman, and electronic spectra of the com pounds of M0204F~- and M020 4F3- confirm that they all contain the dioxo-di-fl-oxo-dimolyb date(V) group [19, 28, 29]. Fig. 53. Structure of the M020 4F4(H20W anion in (NH4h[M0204F4(H20h] [29]. Gmelin Handbook Mo Suppl. Vol. B 5 218 Molybdenum Oxide Fluoride Ions For M020 4Ps- the existence of a triply bridged dinuclear complex with two oxygen atoms and one fluorine atom as bridging atoms has been discussed. This species which was only isolated as crystalline K3[M020 4Fs] exhibits an electronic spectrum similar to those of alt other complexes containing the M020 4 group. It mayaIso be formulated as K2[M020 4F4]· KF [19]. X-ray crystallographic studies of (NH4h[M020 2F9] show that it contains two nonequivalent dinuclear anions M020 2Pg- (one with m symmetry, the other is centrosymmetric). They are built up from octahedra sharing a corner occupied by a fluorine atom, OF 4Mo--Fbr-MoF 40. The oxygen atoms lie in the positions trans to the bridge bond. Selected atomic distances (in A) and angles for the anion with m symmetry, 0(1)F4Mo(1)--F(1)--Mo(2)F40(2): Mo(1)-F=1.84(2) and 1.89(2), Mo(1 )--0(1) = 1.82(3), Mo(1 )--F(1) = 2.19(2), Mo(2)--F(1) = 2.18(2), Mo(2)-F = 1.96(2) and 1.99(1), Mo(2)--O(2) = 1.64(2); 0(1 )--Mo(1 )--F(1) = 173(1 )0, Mo(1 )--F(1 )--Mo(2) = 164.2(7t. Values for the centrosymmetric 0(3)F4Mo(3)-F(2)--Mo(3)F 40(3): Mo(3)--F = 1.891 (15) and 1.943(13), Mo(3)--O(3) = 1 .693(13), Mo(3)--F(2) = 2.118(2); O(3)--Mo(3)--F(2) = 175.6(5t, Mo(3)--F(2)--Mo(3) = 180.0° [5, 30]. The 0.001 M aqueous solution of the M2[M020 4F4] compounds with M = Cs and bipyH (bipy = bipyridyl) show a conductivity of 405 and 230 Q -1. mol-1. cm2, respectively [19]. Susceptibility measurements by the Gouy method [19,29] indicate diamagnetic anions [29]; f.leff = 0.21, 0.24, and 0.25 f1s per Mo atom result for M = phenH (phen = phenanthroline), bipyH, and Cs salts, respectively [19]. The vibrational spectra of M2[M020 4F4] have been studied on M = N(CH3)4 [29], Cs, bipyH, and phenH [19]. IR and Raman spectra for the M = N(CH3)4 salt follow [29]: IR frequency in cm-1 .. 970 vs (952 s) 938 s 750 sh 738 vS,br Raman shift in cm-1 ... 971 vs (948 m) 931 m 749 m,br assignment ...... v(MO=O) from N(CH3)4 v(MO=O) v1 or V2 (M0202) V1 or V2 (M0202) IR frequency in cm-1 .. 515 m 475 s 461 s 434m 325m- 305 s Raman shift in cm-1 ... 454 w - 363 m, 318w 216 s assignment ...... v3(Mo202) v3(Mo202) v(MoF) v(MoF) deformation modes vS(M0202) The assignment V1 indicates the A1 breather mode of the M020 4 ring; V2 denotes the 8 1 mode with both oxygen atoms oscillating in phase along the (Iong) diagonal 0--0 of the M020 4 ring with the Mo atoms oscillating anti parallel to the oxygen atoms; v3 denotes the 82 mode with the Mo atoms oscillating in phase along the (short) diagonal Mo--Mo of the M020 4 ring and with the oxygen atoms oscillating anti parallel to the Mo atoms; Vs is the A1 ring-deformation mode with the 0--0 diagonal stretching and compressing out-of-phase with the Mo--Mo stretching vibration. Optical spectra from Nujol mulis show absorption bands at 22200, 23200, and 24300 cm-1 for M = Cs, bipyH, and phenH, respectively. In the reflectance spectra the bands occur at 21000 (Cs), 22700 (bipyH), and 23200 cm-1 (phenH), respectively. With the reddish brown M = Cs and bipyH salts an additional band occurs at 30000 and 31200 cm-1, respectively [19]. The M = N(CH3)4 compound is brick red. Note that red-brown colors have been observed with the M020 4F3- anion [29]. The IR and Raman spectra observed with (NH4MM020 4F4(HPh] between 200 and 1000 cm-1 are as follows (for the designations V1' V2' V3' and Vs, see above) [29]: IR ...... 980 vs 954 s 775 sh, 742 s,br 625 m,br 500 m Raman ...... 973 vs 958 m 745 m,br 500 w assignment ...... v(MO=O) v(MO=O) v1 or v2(MoP2) GmeLin Handbook Mo Suppl. Vol. B 5 OxofLuoromolybdates(V) 219 IR ...... 445 vs 350 w, 317 w 290 m 210 vs Raman ...... 367 m, 324 w 298 w assignment ...... v(Mo-F) deformation modes The conductivity of the 0.001 M aqueous solution of K3[MoP4FS] is 480Q-1. mol-1. cm2. For K3[M020 4Fs] a magnetic moment Ileff of 0.10 !!B per Mo atom was determined by the Gouy method. Very strong IR bands at 960 and 955 cm-1 are attributed to v(MO=O), a strong band at 740 cm-1 is attributed to the annular Mo02Mo group. For other bands between (in cm-1) 310 w and 3540 (!) m, see the paper. UV-visible spectra show absorption bands at 20000 and 28500 cm-1forthe Nujol mull; refLectance spectra show bands at 20000, 25000, and 33300 cm-1 [19]. The red-brown salts (NH4MM020 4Fs] and Na4[M020 4Fs]·3NaF show at room temperature a magnetic moment per Mo atom of Ileff=0.56 and 0.43 !!B' respectively, as found by the Gouy method [29]. By the same method, !!eff=0.18 !!Bper Mo atom is given for a light yellow salt formulated as Cs4[M020 4Fs] [19]. For (NH4MM020 4Fs], the IR and Raman spectra between 200 and 1000 cm-1 are as follows (the designations V1' V2' V3' and Vs are explained above) [29]: IR ...... 950 vs 910 m, 890 mal 735 s 705 sh 505 s Raman ...... 950 vs 907 m 733 m assignment ...... v(MO=O) v(MO=O) V1 or V2 (M020 2) IR ...... 455 s,br 400 sh b) Raman ...... 450 w,br - 386 237 m 222 m assignment ...... v(Mo-F) v(Mo-F') deformation mode vS(M020 2), v(Mo-O) a) Split by interaction with 2 v(Mo-F). - b) F': in trans position to MO---D. The magnetic data show that between 80 and 295 K M3[M020 2Fg] (M = NH4 or Cs) follows the Cu rie law exactly, however, with an effective moment of 1.51 (2) !!B. The reduction below the spin-only value is attributed to the admixture of -10% MOVI rather than to antiferromagnetic exchange. For data of vibrational spectra, see the papers [5,30]. References: [1] Sunil, K. K.; Rogers, M. T. (Inorg. Chem. 20 [1981] 3283/7). [2] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii], V. D. (Chem. Phys. 71 [1982] 145/56). [3] Sunil, K. K.; Harrison, J. F.; Rogers, M. T. (J. Chem. Phys. 76 [1982] 3087/97). [4] Chakravorti, M. C.; Pandit, S. C. (J. Coord. Chem. 5 [1975/76] 85/9). [5] Mattes, R.; Mennemann, K.; Jäckel, N.; Rieskamp, H.; Brockmeyer, H.-J. (J. Less-Common Metals 76 [1980] 199/212, 201, 211). [6] Garif'yanov, N. S.; Kamenev, S. E.; Ovchinnikov, I. V. (Zh. Fiz. Khim. 43 [1969]1091/5; , Russ. J. Phys. Chem. 43 [1969]611/3). [7] van Kemenade, J. T. C. (Recl. Trav. Chim. 89 [1970] 1100/8). [8] Wentworth, R. A. D.; Piper, T. S. (J. Chem. Phys. 41 [1964] 3884/9). [9] Manoharan, P. T.; Rogers, M. T. (J. Chem. Phys. 49 [1968] 5510/9). [10] Grandjean, D.; Weiss, R. (Compt. Rend. C 263 [1966] 58/9). [11] Grandjean, D.; Weiss, R. (Bull. Soc. Chim. France 19673054/8). [12] van Kemenade, J. T. C. (Recl. Trav. Chim. 92 [1973]1102/20). [13] Dubrov, Yu. N.; Marov, I. N.; Belyaeva, V. K.; Ermakov, A. N. (Zh. Neorgan. Khim. 17 [1972] 2448/55; Russ. J. Inorg. Chem. 17 [1972] 1278/82). [14] Dalton, L. A.; Bereman, R. D.; Brubaker, C. H., Jr. (Inorg. Chem. 8 [1969] 2477/80). Gmelin Handbook Mo Suppl. Vol. B 5 220 MOlybdenum Oxide Fluoride Ions [15] Kalbacher, B. J.; Bereman, R. D. (Inorg. Chem. 14 [1975] 1417/9). [16] Marov,I. N.; Dubrov, Yu. N.; Belyaeva, V. K.; Ermakov, A. N. (Zh. Neorgan. Khim. 17 [1972] 2666/76; Russ. J. Inorg. Chem. 17 [1972]1396/402). [17] Sakai, S.; Nishikawa, M.; Tsuru, N.; Yamashita, T.; Ohyoshi, A. (J. Inorg. Nuel. Chem. 41 [1979] 673/80). [18] Beuter, A.; Sawodny, W. (Z. Anorg. Allgern. Chem. 427 [1976] 37/44). [19] Chakravorti, M. C.; Bera, A. K. (Transition Metal Chem. [Weinheim] 8 [1983] 83/6). [20] Marov, I. N.; Belyaeva, V. K.; Dubrov, Yu. N.; Ermakov, A. N.; Korovaikov, P. A. (Zh. Neorgan. Khim. 15 [1970] 3265/70; Russ. J. Inorg. Chem. 15 [1970]1701/4). [21] Abdraehmanov [Abdrakhmanov], R. S.; Ivanova, T. A. (J. Mol. Struet. 19 [1973]683/92). [22] Verbeek, J. L.; Vink, A. T. (Reel. Trav. Chim. 86 [1967] 913/9). [23] Wendling, E.; de Lavillandre, J. (BulI. Soe. Chim. Franee 1967 274317). [24] Wendling, E. (Rev. Chim. Minerale 4 [1967] 425/46). [25] Garif'yanov, N. S.; Fedotov, V. N.; Kueheryaenko, N. S. (Izv. Akad. Nauk SSSR Sero Khim. 1964 743/5; Bull. Aead. Sei. USSR Div. Chem. Sei. 1964 689/91). [26] Dubrov, YU. N.; Marov, I. N.; Belyaeva, V. K.; Ermakov, A. N. (Zh. Neorgan. Khim. 17 [1972] 3180/3; Russ. J. Inorg. Chem. 17 [1972]1672/5). [27] Chakravorti, M. C.; Pandit, S. C. (J. Indian Chem. Soe. 50 [1973] 618/20). [28] Mattes, R.; Lux, G. (Angew. Chem. 86 [1974] 598/9; Angew. Chem. Intern. Ed. Engl. 13 [1974] 600). [29] Mattes, R.; Lux, G. (Z. Anorg. Allgern. Chem. 424 [1976]173/82). [30] Mattes, R.; Mennemann, K.; Rieskamp, H.; Broekmeyer, H.-J. (Chem. Uses MOlybdenum, Proc. 3rd Intern. Conf., Ann Arbor, Mich., 1979, pp. 28/33). 2.4.2.2.3 Oxofluoromolybdates{Vl) Many oxofluoromolybdate(VI) anions are deseribed in the literature to exist in salts and/or in solutions. The structures of some salts are known from erystal strueture determinations, however, others and those in solution have been investigated only by 19F NMR and vibrational speetra. MoO(OH)2F:;- and MoO(OH)F.!. These anions form by treatment of a 20 wt% solution of MoOF4 in CH 3CN with a 20 wt% solution of H20 in CH 3CN (see p. 205). They yield the following 19F NMR parameters (ö1, ö2, ö3 >0 for upfield shifts; ö(HF) =179.1 ppm, JHF =400 Hz; aeeording to a figure in the paper, ö(HF)= 172 ppm) [38]: anion ö1 in ppm ö2 in ppm ö3 in ppm J1- 2 in Hz J2-3 in Hz faee-MoO(OH)2F3" 22.5 90.8 61 eis-MoO(OH)F", -35.5 -30.5 114.5 57 61 MoOF;". There is evidenee from the Raman speetrum that the MoOFs ion forms in liquid HF when MoF6 is hydrolyzed by H20 at mole ratios MoF6 :H20=1:3 and 1:2 [7]. lonization of MoOF4 in anhydrous HF to give the MoOFs speeies eould not be observed [8]. In the MoOFcHF-NOF system formation of the MoOFs was deteeted by Raman speetroseopy and the solid eompound (NO) [MoOFs] was isolated. Analogously, MoOF4 and ClOF3 form the solid eompound (ClOF2) [MoOFs] whieh exhibits an ionie strueture [1], cf. also p.203. 19F NMR indieate the formation of MoOFs in solutions of Mo02F2 in HF and S02ClF + HF mixtures [46]. GmeLin Handbook Mo Suppl. Vol. B 5 OxofLuoromoLybdates(VI) 221 Thermographic studies of mixtures of MoOF4 with fluorides MF (M = K, Rb, Cs) show great tendencies of the oxide fluoride to form compounds of the type M[MoOF5] [9]. Solid com pounds of this composition aLso form by the reactions of moist CsF with MoF6 in IF5 or S02' of Cs2[Mo02F4] with MoF6 in S02' and of K2Mo04 with anhydrous HF [10]. Cs[MoOF5] can be prepared by partial hydrolysis of Cs[MoF7] [47]. Solutions of 5.8 mol% (NOh[MoOF6] in propylene carbonate have been studied at 10°C by 19F NMR (external standard: CCl3F). A doublet and a quintet (for both JF- F = 50 Hz) were observed at a downfield shift of 127.0 ppm and an upfield shift by 47.1 ppm, respectively [1]. A shift by 140 ppm (presumably downfield) is given in [46]. With (NOh[MoOF6] solutions in propylene carbonate shaken with NOF at 10°C, the doublet and the quintet (for both JF_F =49 Hz) occur at 128.6 and 127.9 ppm downfield and at 68.2 and 69.5 ppm upfield for fresh and 24 h old solutions, respectively. For shifts observed in HF solutions, see the paper [1]. Vibrational spectra have been recorded for M[MoOF5]: IR and Raman spectra with M = Cs [47] and with M = NO [1]; Raman spectra with M = ClOF2 [1]; for M = NO, also see the IR study [48]. With M = NO, IR bands were found at 643 and 988 cm-l [48], Raman shifts and IR frequencies attributed to the MoOF5" ion were found and assigned as follows (intensities are given in parentheses) [1]: Raman shift in cm-l ... 985(10) 665(7.2) IR frequency in cm-l 650 vS,br type of vibration MO--0 sym. in-plane MoF4 antisym. in-plane MoF4 symmetry species Al Al E Raman shift in cm-l ... 557(0.6) 317(6.2) IR frequency in cm-l 550 sh 436 m type of vibration sym. out-ot-phase MoF4 Mo-Fax ö(0=MoF4) or ö(Fax-MoF4) symmetry species ..... 81 Al E E With M = ClOF2, Raman shifts attributed to MoOF5" are found and assigned as follows (intensities are given in parentheses) [1]: Raman shift in cm-l ... 1011 (1 0) 680(10) 650(6) type of vibration MO=O sym. in-plane MoF4 antisym. in-plane MoF4 symmetry species ..... Al Al E Raman shift in cm-l •.. 548(1) 316,319(8.6) type of vibration sym. out-of-phase MoF4 ö(O=MoF4) or ö(Fax-MoF4) symmetry species 81 E E With M = Cs, Raman shifts and IR frequencies attributed to the MoOF5" ion are as follows [47]: Ranian shift in cm-l ... 973 vs 666 m -580 IR frequency in cm-l 973 vs 662 vw 605 vsa) type of vibration MO=O MoF4 MoF4 MoF4 symmetry species .... . Al Al E 81 Raman shift in cm-l .. . 324 m IR frequency in cm-l 492 m 300 w 252 s type of vibration Mo-Fax ö(O=Mo-F) ö(MoF4) ö(MoF4) symmetry species Al E Al E a) Note that this very strong band has no counterpart in the spectra with M = NO or ClOF2 recorded by [1]. Gmelin H~ndQook MQ suppl. Vol. B 5 222 MoLybdenum Oxide FLuoride Ions VaLence force constants of 7.56, 3.65, and 2.35 mdyn/A have been derived for Mo=Ü, Mo-Feq , and Mo-Fax, respectiveLy [47]. MoOFr ions, apparently formed by the equiLibrium MoOF5' + HF2~HF + MoOF~-, have been detected by Raman spectroscopy using saturated soLutions of (NOMMoOF6] in NOF, 2.7 HF mixtures at 1Q°C. The shifts 962 and 595 cm-1 were assigned to the Mo=ü stretch and the symmetric in-pLane Mo-F stretch, respectiveLy. 19F NMR did not detect any shift distinguishing this ion from the MoOF5' ion abundant in the soLution [1]. Mo02(OH)F2H20-. This species forms as a resuLt of the proton dissociation of Mo02F2·2H20 in aqueous soLution. It was studied by 19F NMR as described for Mo02F3HP- (see beLow). UpfieLd shifts by löl = 506 and 729 ppm are attributed to the Mo02(OH)F2H20- ion which is beLieved to contain the pairs F-F and 0-0 in cis arrangements [49]. Mo02F3", [M002FJ~-, n =2,00. The occurrence of the Mo02F3 species in the mass spectrum of a mixture of MoF3 and KBe2Fs in the presence of oxygen-containing impurities is reported in [11]. In aqueous soLution, Mo02F3 forms during the reaction ot Mo02F2 with HF at moLe ratios HF: Mo02F2 ranging from 0.1 to 1.0 [12], aLso see [13]. In soLutions of ammonium moLybdate in aqueous HF the ion was spectrophotometricaLLy detected at HF concentrations of 0.16 to 0.53 M [14]. The stabiLity of this species in aqueous HF is ten times Less than that of the M002F~- species (see beLow). The instabiLity constant (1.22 ± 0.1) x 10-3 was determined by an anion exchange method [12]. Solid saLts of the type M[Mo02F3] with M = K, Rb, or Cs have been precipitated trom soLutions of Mo02F2 in excess hydrofLuoric acid by adding stoichiometric amounts of MF (M = Rb, Cs), from soLutions ot M2[Mo02F4]· H20 in 70 wt% aqueous HF (M = K), and trom M2[Mo02F4] in aqueous 40 wt% HF by evaporation (M = Rb, Cs) [4]. ALso Mo03 reacts with equivaLent amounts of M2C03 in 40 wt% aqueous HF (M = NH4 , K, Rb, Cs); tor M = TLi, Mo03 has to be in excess [15]. NH4 [Mo02F3] forms by thermaL decomposition ot (NH4MMo02F4] at 210 to 230°C [52]. A singLe crystaL X-ray anaLysis and vibrationaL spectra of Cs[Mo02F3] show that in the solid state, the anion i!> poLymerized into infinite chains. The octahedraLLy coordinated Mo atoms are Linked by cis-bridging F atoms. The two terminaL cis °atoms are copLanar with the bridging F atoms. The bridging Mo-Fb, distance is 2.11 ± 0.01 A and the Fb,-Mo-Fb, angLe is 81°. Other distances: Mo-F = 1.89 ± 0.06, Mo-O = 1.68 ± 0.06 A; for other distances and angLes see the paper [15]. A dimeric structure of the anion with overall symmetry cLose to D2h , see Fig. 54, was proved for the crystaLLine compound containing the buLky cation [MOO(S2CN(C2Hshh]+. The main difference trom the poLymeric structure described above is the existence of di-f.t-fLuoro bridges in the dimeric structure. The oxygen and terminaL fLuorine atoms have the same Locations reLative to the bridge, and angLes and Mo-O and Mo-F distances are simiLar in both structures. Bond Lengths were determined as toLLows: Mo(2)-Q(2) = 1.667(7), Mo(2)-Q(3) = 1.690(7), Mo(2)-F(1) = 1.921 (5), Mo(2)-F(2) = 1.846(6), Mo(2)-F(3) = 2.141 (4) A. SeLected bond angLes: Mo(2)-F(3)-Mo(2) = 110.7(1 t, F(3)-Mo(2)-F(3) = 69.0(2t. The Large counter ion may have a profound effect in stabiLizing the dimeric structure [16]. Gmelin Handbook Mo Suppt. Vot. B 5 Oxofluoromolybdates(VI) 223 F(ZI Fig. 54. Strueture of the M020 4Ft anion in erystalline [MoO(S2CN(C2HshhblM0204Fs] [16]. Raman shifts and IR frequeneies are plotted for Cs[Mo02F3] for the ranges 200 em-l ~v~ 1000 em-l . The following features were found [15]: Ramanshiftincm- l .. 974vs 912s 580ma) IRfrequencyincm-1 .. 970s 919vs -600sh 581vsb) 449m 418sh 411 m assignment ...... vsym(Mo02) vas(Mo02) - a). b) vas(Mo-Fbr-Mo) - vas(Mo-Fbr-Mo) Ramanshiftincm-l .. 403 m 308 m 282 sh 268 s 242 m IRfrequencyincm-1 .. 393 m 380 sh 293 ms 279 sh assignment ...... ö(Mo02) ö(Mo02) ö(MoF2 or Q-Mo-F) a) In the text: weak, attributed to vs(FcMo-Ft). - b) In the text: 579 cm- 1, attributed to vas(FcMo-Ft). The IR speetrum of NH4[Mo02F3] is plotted between 400 and 3600 em-l . The two intense bands in the range 900 to 1000 em-l are attributed to vibrations of the Mo02 group [52]. The IR speetra of M2[Mo02F3], M = K, Rb, Cs, plotted for 400 to 2000 em-l have been attributed to isolated anions; the speetrum for M = K has been tentatively attributed to dinuelear (Mo02F2F2,;h ions [50]. The di-Wfluoro-bridged speeies has been studied by IR speetroseopy on [MOO(S2CN (C2HshhblM0204Fs]. While the point group of the anion is C2, its geometry is elose to D2h symmetry. The following IR frequeneies have been found and assigned to for it [16]: V in em-l ...... 956 922 544 assignment ...... Mo.--D Mo.--D Mo-Ft Mo02F3H20-. The formation of this speeies was observed when triethylamine was added to solutions of the oxohydroxoaquofluoro eomplexes produeed by the hydrolysis of MoOF4 in CH 3CN (see p.205) [38]. From the Raman speetrum it was dedueed that the speeies Mo02F3H20- (or the hydrate Mo02F2 ·2H20) with a cis arrangement of the ° atoms exists in solutions of sodium molybdate or Mo03 in aqueous 5 M HF [51]. Formation of this ion in solutions of Mo03 in 40 wt% HF has been established by NMR on addition of methanol [49]. Solutions of Mo03 in 40% HF have been studied at - 80 to + 30°C after addition of 40% methanol. Upfield shifts by löl = 506 and 546 ppm with respeet to F2 resulted for the doublet and triplet due to Mo02F3H20-; JF_F =69±2 Hz [49]. In CH 3CN, the mer-Mo02F3HP- ion has been suggested. The 19F NMR parameters are: Öl = 17.8, ö2 = 98.0 ppm (upfield shifts; ö(HF)=179.1 ppm, aeeording to a figure in the paperö(HF) =172 ppm); JI_2=50 Hz (J HF =400 Hz) [38]. GmeLin Handbook Mo Suppl. Vol. B 5 224 MoLybdenum Oxide Fluoride Ions The IR frequencies observed on Mo03 in 5 M HF are compared with the Raman shifts (intensities in parentheses) of a soLution of Mo02F3H20- (apparentLy in 5 M HF) [51]: Raman shift in cm-1 ...... 964(10)p 933(6)dp 379(1j2) 277(2) IR from Mo03 in 5 M HF ...... 964 m 929 s assignment ...... v(Mo=ü) v(Mo=ü) Ö(MO----Q) ö(Mo-X) The simuLtaneous appearances of v(Mo=ü) in the IR and the Raman spectra suggest that the oxygen atoms in the Mo02F3H20- ion are in a cis arrangement [51]. M002F~-. This species is the most stabLe form of moLybdenum(VI) oxide fluoride in aqueous soLution [17]. Its formation in aqueous HF soLutions of Mo02F2 was observed at moLe ratios HF: Mo02F2 ranging from 1 to 10 [12], see aLso [13, 17]. The instabiLity constant of the anion in aqueous HF, (1.47 ± 0.2) x 10- 4 was determined by an anion exchange method [12]. The inter action between (NH4)2Mo04 and NaF in diLute aqueous soLution at pH 3 and 20°C Leads to the formation of the Mo02Ft ion in the region of high NaF concentrations. SoLutions with totaL moLar concentrations of 0.5 x 10- 4 to 2.0 x 10- 4 were studied by a spectrophotometric variant (/...= 250 nm) of the method of isomolar series, and the method of equiLibrium shift was appLied to soLutions of constant concentration of MoO~- (2.0 x 10-4 M) and various concentrations of F- (0.8 X 10-4 to 3.2 X 10-4). From these data the instabiLity constant 2.6 X10-11 was caLcuLated [18]. SoLid compounds M2[Mo02F4] with M = Rb or Cs can be prepared from soLutions of Mo03 in aqueous HF by adding the aLkali fluorides at moLe ratios Mo03 :HF:MF =1:2:3 [4], or from soLutions of Mo03 in 40 wt% aqueous HF by adding the corresponding carbonates untiL pH 4 [2]. With M = K onLy the hydrate K2[Mo02F4]· H20 precipitates in the systems Mo03-KF-HP [5] or Mo03-KF-HF-H20 [4,6] or from soLutions of K2Mo04 in 40 wt% aqueous HF [6]. The (NH4MMo02F4] can be obtained from the reactions of NH4HF2 with Mo03 at 105 [2] to 110°C [52] or with (NH4)6M07024·4H20 at temperatures up to 500°C [19]. The (NH4h[Mo02F5J, wh ich was isoLated from soLutions of Mo03 + (NH4hC03 in 40 wt% HF, decomposes at 135°C to give the (NH4MMo02F4] [2]. Solid saLts (bHMMo02F4] and (b'H2)[Mo02F4] with numerous organic monoacid (b, e.g. quinoLine, guanidine) and diacid bases (b', e.g. ethyLenediamine) were prepared by reacting soLutions of the organic bases with Mo03 in 40 wt% aqueous HF (base: Mo03 =5:1) [20]. SaLts of composition M2[Mo02F4] with M = NH4, Rb, or Cs have been investigated by IR, Raman, and 19F NMR spectroscopy, and by X-ray diffraction. They show that in the solid state and in soLution the Mo02Ft ion has an octahedraL configuration with a nonlinear (cis) arrangement of the 0 atoms in the Mo02 group [2, 17, 21, 22] and that there are two nonequivaLent groups of fLuorine atoms in the cis and trans positions with respect to the oxygen atoms [17, 23]. C2v symmetry of the octahedra is stated for the crystaLLine compounds [2] and is also assumed in soLution [24]. The Lower Cssymmetry for the anion in the crystaLLine saLt K2[Mo02F4]· H20 which resuLts from the X-ray structure anaLysis is due to the internaL contacts of the M002F~- group with the H20 moLecuLes and K+ ions [24 to 26]. The vibrationaL spectra indicate C2v symmetry aLso in this case [26]. In K2[Mo02F4]·H20 the foLLowing atomic distances and angLes have been found (seLected vaLues): Mo-F =1.930 to 2.002 A, Mo-O =1.688 and 1.733 A; O--Mo-O = 95°1 0' [24]. In the anhydrous K2[Mo02F4] (which was prepared from the monohydrate by heating at 100°C in vacuum) the 0 and F atoms in the anion are ordered and the C4v symmetry of the octahedra was determined by eLectron diffraction. The ordered array of the oxygen atoms gives rise to an anion with trans figuration of the oxygen atoms in the Ligand sphere. In this configuration, a shortening of onLy one Mo-O(1) distance (1.67 A) was observed, indicating a multipLe bond. This effect causes a shift aLong the fourfoLd axis of aLL the Ligand spheres, and this moves the Mo atom about 0.17 A from the equatoriaL pLane. Interatomic Gmelin Handbook Mo Suppl. Vol. B 5 Oxofluoromolybdates(VI) 225 distances: Mo-F =1.87, Mo-O(2) =1.99 A [27]. An X-ray structure determination of Rb2[Mo02F4] shows the anion to be tetragonal bipyramidal with fluorine atoms on the bipyramid axis. The equatorial plane contains two oxygen and two fluorine atoms wh ich are statistically distributed in the coordination positions. The Mo-F distances are 2.00 and 2.02 A, while the Mo-(O,F) distances are 1.90 A [53]. The 19F NMR of 60% (NH4h1Mo02F4] solutions is consistent with oxygen in cis arrangement. The spectrum shows a broad line shifted by löl = 542.8 ppm and a narrow line shifted by löl = 507.6 ppm (with respect to F2) [23]; the values 541.4 and 510.8 ppm have been given for aqueous (H20) solutions at -10°C; solutions in D20 show -0.8 ppm larger shifts (indicating hydration numbers of 2.1 to 2.2 for the M002F~- species) [54]. The broad line is aUributed to the fluorine atoms coplanar with the cis-oxygen atom pair, the narrow line is attributed to axial fluorine atoms arranged normal to that plane. Addition of ~5% NH 4Fto the solution influences both form and position of the resonances (the broadness of wh ich obviously reflects exchange of F- with the solution). For ~ 5% NH 4F, both lines split into triplets (J F- F = 62 Hz), the low shift (narrow) line moving to higher shifts, the high shift (broad) line moving to lower shifts [23]. Also see [17,38]. Raman and IR spectra of the saturated aqueous solution of Na2[Mo02F4]· H20 are as folio ws (Raman intensities in parentheses) [37]: Raman shift in cm-1 951 (10)p 920(7)dp 385(1 ) 293(1 ) IR frequency in cm-1 .... 948 m 912 vs The Raman and the IR spectra of crystalline K2[Mo02F4]·H20 are given (with controversal assignments) in [26,37]. A further set of vibrational frequencies and assignments is given in [15]. IR spectra for M2[Mo02F4] (M = Rb, Cs) are given for 400 to 2000 cm-1 in [50]. Assigned IR and Raman spectra are given for M = NH 4 , Rb, and Cs in [22]; for M = NH 4 also see [52]. For M = Rb Raman shifts and IR frequencies (in cm-1) are as follows [22]: Raman shift ...... 944 vs 898 m 557 w,br IR frequency ...... 943 s 895 vs 548 vs 535 sh,s assignment ...... vs(Mo02) vas(Mo02) vs(MoF2) vas(MoF2),Vs(MoF2)a) Raman shift ...... 396 m to s 311 s 298 sh,m IR frequency ...... 442 s 418 w 400 sh,w 355 vw 315 w 290 sh,w assignment ...... vas(MoF2) ö(Mo02) ö(MoOF) Raman shift ...... 225 vw,br IR frequency ...... 278 s 260 sh,w 254 sh,w 247 m 223 m assignment ...... ö(MoF2) y(Mo02) y(MoF2) Raman shift ...... 160 m,br 89 m,br IR frequency ...... 208 vw assignment ...... ,(MoF2) ,(Mo02) external (lattice) vibration a) F' = axial F or in trans position to O? The IR frequencies of isotopically substituted Cs2[Mo02F4] have been studied with the following results [55]: species ...... Cs2[Mo 1602F 4] Cs2[Mo 160180F 4] Cs2[Mo 1802F 4] Vs in cm-1 •.•••..•... 944 914 893 Vas in cm-1 •.••...•.. 894 875 852 GmeLin Handbook Mo Suppl. Vol. B 5 15 226 Molybdenum Oxide Fluoride Ions The force constant K{MO---o) = 6.85 mdyn/A was derived [55]. For similar values and further force constants (calculated for a range of models in view of the uncertainty of the assignments used), see [26]. M002F~-. {NH4h[Mo02Fs] forms {together with (NH4MMo02F4]) by heating MoOa and NH4HF2 in the mole ratio 1:3 at 70°C. Partial formation of {NH4b1Mo02Fs] takes place when an equimolar mixture of NH4F and {NH 4MMo02F4] is heated in sealed Teflon ampules [52]. The following vibrations of crystalline (NH4b1Mo02Fs] have been attributed to the Mo02Fr ion [22]: Raman shift in cm-1 ...... 958 sh,w 949 vs 931 vw 912 m IR frequency in cm-1 955 m 948 m 923 sh,m 910 s 898 sh,m assignment ...... vs{Mo02) vs{Mo02) vas{Mo02) vas{Mo02) vas{Mo02) Raman shift in cm-1 ...... IR frequency in cm-1 600 sh,w 578 sh,m 560 s 530 m 425 sh,w assignment ...... v{MoF) v{MoF) v{MoF) v{MoF) v{MoF) Raman shift in cm-1 ...... 393 m 306 vs IR frequency in cm-1 418 382 vw 375 vw 305 vw assignment ...... v{MoF) ö{Mo02) ö{Mo02) ö{Mo02) Ö{MoF) Raman shift in cm-1 ...... 214 m IR frequency in cm-1 292 vw 284 vw 268 m 203 w assignment ...... ö{MoF) Ö{MoF) ö{MoF) Ö{MoF) A plot of the IR spectrum between 400 and 3600 cm-1 is given in [52]. Mo02(HF2ß-. The spectrophotometric investigation of molybdate solutions containing HF at various concentrations indicates the formation of stable complex ions with 4 HF2" per MoVlat HF concentrations ranging from 0.53 to 2.6 moVL. The complex species can be formulated as M002{HF2)~- in which F- is bonded to Mo and the HF is a solvating molecule. The stability constant was calculated as log ß4=3.0±0.5 [14], cf. also [56]. MoOaF-. This species was detected in the mass spectrum of NaF vapor at 1050 K probably as a product of areaction between the molybdenum effusion cell, NaF, and oxygen-containing species (HP or CO2) [28]. During the interaction of {NH4hMo04 with NaF in dilute aqueous solutions at pH 3 and 20°C, formation of MoOaF- in addition to M002F~- (see above) was stated. Sy the same method as described for M002F~-, the instability constants for MoOaF- were determined as 3.28 x lO-s and 7.9xlO-4 at MoO~- concentrations 2.0x10-4 and 5x10-a M, respectively [18, 29]. Solid compounds containing the MoOaF- anion are scarce. Colorless Na[MoOaF] has been detected in the NaF-MoOa system and prepared by heating stoichiometric amounts of the components in an O2 atmosphere at 460°C [43]. The RbF-MoOa-H20 system gives Rb[MoOaF] ·0.5H20 [30]. The structure of the MoOaF- ion in the crystalline sodium compound is closely related to that of a-MoOa· H20, see "Molybdenum" Suppl. Vol. S 3a, 1987, p. 31. It is built up by isolated double chains of edge-sharing octahedra with bond lengths Mo-X(1) = 1.698(9), Mo-X(2) = 1.958(7), Mo-X(3) = 2.135(7), and Mo-X(4) = 1.728(8) A, where X is ° or F. For other distances and angles see the paper [44]. The specific positions of oxygen and fluorine atoms have been assigned as shown in Fig. 55 using various techniques such as 19F NMR, Raman spectroscopy, electrostatic energy and site potential calculations, and analysis of local balance between charge of neighboring ions [45]. Gmelin Handbook Mo Suppl. Vol. B 5 OxofLuoromolybdates(VI) 227 0- X(2) Fig. 55. Structure of the Mo03F- anion chain in solid Na[Mo03F] with positions of the ° and F atoms [45]. A plot of the IR spectrum between 400 and 1600 cm-' is given in [30] and that of the Raman spectrum between 200 and 1000 cm-' in [45]. The Raman shifts are assigned as follows [45]: Raman shift in cm-' .. 974.5 906 670 474 413,392 337 245 assignment ...... v(Mo02;A,) v(Mo02;B,) v(M030;B,) v(Mo30;A,) ö(Mo02) ö(Mo30;B2) ö(Mo02) M003~-' Solid compounds containing the M003F~- anion have been identified in the MF Mo03-H20 systems with M = K, Rb, and NH 4. For details of formation see the corresponding systems in a later "Molybdenum" volume. The colorless K and Rb salts crystallize as monohy drates, see e.g. [5,31] and [30], respectively, whereas the ammonium salt is anhydrous [31,32]. In the crystalline salts the existence of polymeric anions as chains of octahedra was already assumed in [5] and confirmed by the three-dimensional structural analysis of (NH4MMo03F2] and the vibrational spectra of the NH4 and K salts. Planar cis-dioxodifluoro units are linked into an infinite chain by alternating long and short Mo-O bridges, see Fig. 56. At the bridging ° atoms the angle Mo-O--Mo = 148.9°, but at the Mo atoms the chain is stretched to give O--Mo-O = 176.5°. For interatomic distances see Fig. 56; other distances and angles are given in the paper [31], see also [57]. The existence of the nonlinear Mo02 group in the anion was also deduced from the IR spectrum of the K salt [33]. Fig. 56. Structure of the M003F~- anion in solid (NH 4MMo03F2] (interatomic distances in A) [31]. IR spectra (v ~400 cm-') are plotted for (NH4MMo03F2] up to 4200 cm-' in [32], for K2[Mo03F2] up to 4000 cm-' in [33], and for Rb2[Mo03F2]· H20 up to 1600 cm-' in [30]. As signed Raman and IR spectra between 200 and 1000 cm-' are tabulated for (NH 4MMo03F2] Gmelin Handbook Mo Suppl. Vol. B 5 228 Molybdenum Oxide Fluoride Ions and K2[Mo03F2]· H20 in [31,37]. These two papers agree in assuming the presence of cis-dioxo O=Mo=ü and !!-OXO Mo-O-Mo groups in these salts. There are, however, considerable discre pancies between the spectra published in these papers [31, 37]. M003F~-. This species has been isolated in the crystalline salts M3[Mo03F3] which occur as stable phases in the MF-Mo03-HzÜ systems with M = K, Rb, Cs, and NH4 at high fluoride concentrations, see, e. g. [5, 30, 32, 34] and in the MF-Mo03 systems with M = Na, K, Rb, and Cs [3]. Details of formation will be described with the corresponding systems in a later "Molybde num" volume. Salts of the type M2M'[Mo03F3] where M and M' are different alkali metal ions (e.g. K2Na, Rb2K, Cs2Rb etc.) have also been prepared [58]. All these solid compounds are colorless. For the complex formation according to Mo03+ 3F-~ M003~-' areaction enthalpy of -115 kcaVmol has been calculated [3]. The structural analysis of the ammonium compound [36] gives evidence for the existence of the M003~- anions as discrete units in the crystal structure [5]. This is confirmed bya later crystal structure determination of K2Na[Mo03F3] [58]; interatomic distances: Mo--F = 1.9 [36], Mo--(O,F) = 1.930 A [58]. The IR and Raman spectra suggest C2v symmetry [26, 35] and a cis configuration of the oxygen atoms [37]. IR spectra of the M003~- ion have been recorded on M2M'[Mo03F3] (M = K or Rb, M' = Na) [35] and M = M' = Rb [30]. The Raman spectrum was recorded with M = M' = K [26]. The early paper [37] favors a 1,2,3 cis (face) occupation, while paper [26] agrees with [35] in assigning to the ligand octahedron an edge rather than a face occupation by oxygen and fluorine atoms. However, several assignments of IR frequencies from [35] have been changed on grounds of force constant calculations in the Later paper [26], see the foLLowing table of IR frequencies and Raman shifts recorded with K2Na[Mo03F3] [35] and K3[Mo03F3] [26], respectively (primed atom symboLs: 0' is in trans position to F' and vice versa [26]): IR frequency in cm-1 .. 916 m 880 sh 845 vs 475 s 405 w assignment [1] ...... vs(Mo02;A1) v(MoO;A1) vas(Mo02;B1) vas(MoF2;B2) v(MoF2;A1) Raman shift in cm-1 .•. 915 vs 845 m assignment [3] ...... v(MoO;A1) v(MoO';A1) v(MoO;B2) v(MoF;B1) v(MoF';A1) IR frequency in cm-1 .. 368 w 297 s,sh 290 vs 230 s assignment [1] ...... v(MoF;A1) y(Mo02;A1,B1,orB2) ö(Mo02;A1,B1,orB2) ö(Mo02;A1,B1,orB2) Raman shift in cm-1 ••• 363 w to m - assignment [3] ...... v(MoF;A1) Ö(Mo0 2;B2) ö(O'MoF;B1) IR frequency in cm-1 •• 212 sh 136, 141 s assignment [1] ...... ö(MoOF;B1,B2) ö(MoF2;Al,B2) Raman shift in cm-1 ••• 160 vw assignment [3] ...... ö(OMoF;B1) + ö(OMoF;B2) 't(OMoF;A2) ö(MoF;A1) + ö(OMoF;B2) For assigned IR and Raman (M = M' = NH4) and IR (M = M' = K) spectra, aLso see [37]; aLso see [32, 34, 58]. M020 2Fg. Formation of the M020 2Fg ion takes pLace in the reactions of MoOF4 with fluoride ion donors of various strength, e. g., with NOF, ClF3, CLOF3, and in small amounts with HF [1]. It forms aLso in soLutions of MoOF4 in CH3CN on addition of H20 [38], HF, or acetylacetone [39], and in solutions of MoOF4 in CH2CL2 or toLuene on addition of triphenylphosphine oxide [40]. The methods used for the isoLation of solid M[MoOF5] salts with M = K or Cs (see above) yieLded the M020 2Fg species as the main product. Thus, the solid Rb[M020 2Fg] can be obtained by reacting MoOF4 with RbF in liquid S02' ProbabLy Rb[M020 2Fg] is coLorLess and the bLue gray coLoration of the specimens is caused by hydrolysis products [10]. Solid compounds of Gmelin Handbook Mo Suppl. Vol. B 5 OxofLuoromoLybdates(VI) 229 composition NO[M020 2F9] and CLOFAM020 2F9] form by the reactions of MoOF4 with NOF and CLOF3, respectiveLy [1]. Investigations of the Rb saLt by NMR and IR spectroscopy show that an Mo-F-Mo bridge exists in the dimeric anion and the oxygen atoms are in terminaL positions trans to the F bridge OMoFc F-F4MoO [10,59]. MOP2F9 was studied in soLution by 19F NMR [1, 38 to 40, 59 to 62] and Raman spectros copy [1] and on Rb[M020 2F9] powder by vibrationaL spectroscopy [10]. In the 19F NMR spectrum the chemicaL shifts in acetonitriLe at -40 to -20°C and with respect to the externaL reference CClsF are löl =141.5 ppm for the doubLet [59] (downfieLd [60]) due to the equatoriaL Feq and löl =135.0 ppm [59] (upfieLd [60]) for the bridging Fbr. The superhyperfine interaction constant J(Fbr-Feq)=56 Hz [59]; aLso see [38, 39, 61]. For the compLex in methyLene chLoride soLution at 240 to 215 K (OC given in the paper obviousLy erroneous), an upfieLd shift by löl=133.20 ppm and a downfieLd shift by 1<">1=142.50 ppm were found for Fbr and Feq, respectiveLy; J(Fbr-F eq) = 54 Hz [40]. In propyLene carbonate, ö = -135 ppm (frequency scaLe) for Fbr [62]. The downfieLd shift by löl =134.5 ppm observed at 15°C in HF obviousLy refers to the intense signaL from Feq [1] (aLL shifts given refer to CCL3F [1,39,40,59 to 62]). The doubLet and the muLtipLet show an intensity ratio of 8:1 [39, 61]. The intensity distribution within the muLtipLet is 1 :3.5:7:9:7:3.5:1 suggesting that this apparent septet is a bLurred nonet [39]. In addition to very weak IR bands at 935,953, and 974 cm-1 and Raman bands at 930 (vw) and 984 (w) cm-1 attributed to hydrolysis products, the foLLowing vibrationaL frequencies have been found with Rb[M020 2F9] [10]: IR frequency in cm-1 1033 w 1022 s 689 sh 660 vs 635 w Raman shift in cm-1 ..... 1033 m 685 s assignment ...... vs(Mo=ü) vs(Mo-F) vas(Mo-F) v(Mo-F) IR frequency in cm-1 422 m 310 w 284 s 270 m Raman shift in cm-1 .. . 576 w 321 m 310 w assignment ...... v(Mo-F) vas(Mo-F-Mo) deformation vibrations M0204F~-. This anion is described together with the monomeric Mo02Fs and the poLymerie [M002F3]~- on p. 222. M0204~-. SaLts of the type M3[M020 4F7] can be obtained from soLutions of Mo03 in hydrofLuoric acid with a moLe ratio of HF: Mo03= 4:1 by the addition of a stoichiometric amount of the aLkali metaL fluorides [4], see aLso [6] (here formuLated as "2M02F2 ·3KF"). The anion is formuLated as a dimeric species in the X-ray diffraction study [6]. The M3[M020 4F7] saLts have been studied by IR and Raman spectroscopy for M = K [37] and by IR spectroscopy for M = K, Rb, Cs [50]. The foLLowing Raman shifts (intensities in parenthe ses) and IR frequencies have been found and assigned for the potassium saLt [37]: Raman shift in cm-1 .... 971 (10) 923(7) 594(1 ) IR frequency in cm-1 967 sh 953 vs 919 sh 900 vs 560 vs assignment ...... vs(Mo02) vs(Mo02) vas(Mo02) vas(Mo02) v(Mo-X) v(Mo-X) Raman shift in cm-1 .... 502(%) 387(1 ) 301 (2) IR frequency in cm-1 463 s 374 m 309 sh 285 s assignment ...... v(Mo-X) v(Mo-X) ö(Mo02) Ö(Mo-X) ö(Mo-X) M0206~-. This species was onLy detected in solid Cs3[MoP6F3] which was identified in the CsF-Mo03-H20 system by chemieal, crystaL-chemicaL, and thermographie methods [34]. The Cs saLt can be prepared by melting stoichiometric amounts of MoF3 and CsF in an O2 Gmelin Handbook Mo Suppl. Val. B 5 230 MoLybdenum Oxide Fluoride Ions atmosphere (600°C) or by adding CS2C03 and then Mo03 to 40 wt% aqueous HF at room temperatu re [41, 42]. The structure of Cs3[M020 sF3] contains isoLated anions M020 SF5- of overall 3m symmetry. The dimeric anion is formed by two face-sharing octahedra. In the octahedra, the Mo atoms are shifted towards the terminaL Ligands. The vibrationaL spectra prove that oxygen atoms occupy not onLy terminaL but aLso bridging positions. It has been assumed that a di-,,-oxo-,, fLuoro-bis(dioxofLuoromoLybdate) ion, 02FMo02FMo02P-, is the main species. Bond dis tances are Mo-O = 1. 757(8), Mo-F = 2.152(4), and Mo-Mo = 3.205(3) A, and bond angLes D-Mo-O=103.9(4t, D-Mo-F=90.4(5)O, F-Mo-F=70.6(6t, and Mo-F-Mo= 96.3(9t [41, 42]. IR and Raman spectra support the presence of terminaL cis-dioxo groups (and even monooxo groups) in addition to terminaL cis-trioxo groups. A broad Raman band at 730 to 740 cm-1 is attributed to an antisymmetric Mo-D-Mo bridge mode and the two most intense Raman bands, at 930 and 847 cm-1, are assigned to vs(Mo02) and vas(Mo02), respectiveLy. For plotted IR and Raman spectra, see the papers [41, 42]; aLso see [34]. M0306F~1. PoLymeric oxofLuoromoLybdates are said to be prepared according to [6], however, no detaiLs are given either in [6] or in [37]. This poLymeric species seems to contain cis-dioxo groups. The IR spectrum of (NH4ls[M030sFll]·H20 was assigned as foLlows [37]: IR frequency in cm-1 959 s 894 vs 554 vs 435 s 273 vS,br assignment ...... vs(Mo02) vas(Mo02) v(Mo-X) v(Mo-X) Ö(Mo-X) M040 13P-. The coLorLess K3[M04013F]·3H20 forms in the KF-Mo03-H20 system [5]. It can be prepared from K2Mo04 and hydrofLuoric acid on heating [6]. The foLlowing Raman shifts (intensities in parentheses) have been found and assigned [37]: Raman shift in cm-1 ... 947(10) 929(4) 899(6) 750(V2) 652 vw assignment ...... vs(Mo02) vs(Mo02) vas(Mo02) v(Mo-X) Raman shift in cm-1 ... 555 vw 459 vw 361 (2) 230(V2) assignment ...... v(Mo-X) v(Mo-X) Ö(Mo02) Ö(Mo-X) M06011F12~-. RecrystaLlizing K2[Mo02F4]· H20 from hydrofLuoric acid resuLts in the formation of Kl0[MosOllF24] [4,6]. It is assumed that the compound may be considered as 4KAMo02F4] . K2[M020 3Fa] [6]. References: [1] Bougon, R; Bui Huy, T.; Charpin, P. (Inorg. Chem. 14 [1975]1822/30). [2] Pausewang, G. (Z. Naturforsch. 26b [1971]1218/20). [3] Schmitz-Dumont, 0.; Heckmann, I. (Z. Anorg. ALlgem. Chem. 267 [1951/52] 277/92). [4] BusLaev, Yu. A.; Davidovich, R L. (DokL. Akad. Nauk SSSR 164 [1965]1296/9; DokL. Chem. Proc. Acad. Sci. USSR 160/165 [1965]1009/12). [5] Schmitz-Dumont, 0.; Opgenhoff, P. (Z. Anorg. ALlgem. Chem. 275 [1954] 21/31). [6] BusLaev, Yu. A.; Davidovich, R. L. (Zh. Neorgan. Khim. 10 [1965]1862/71; Russ. J. Inorg. Chem. 10 [1965]1014/20, 1019). [7] SeLig, H.; Sunder, W. A.; Schilling, F. C.; FaLconer, W. E. (J. FLuorine Chem. 11 [1978] 629/35, 634). [8] Paine, R T.; Quarterman, L. A. (Inorg. NucL. Chem. H. H. Hyman Mem. VoL. 197685/6). [9] NikoLaev, A. V.; OpaLovsky [OpaLovskiij, A. A.; Federov, V. E. (Therm. Anal. Proc. 2nd Intern. Cont., Worcester, Mass., 1968 [1969], VoL. 2, pp. 793/810, 799/800). Gmelin Handbook Mo Suppt. Vot. B 5 Oxofluo ro molybdates(VI) 231 [10] Beuter, A.; Sawodny, W. (Angew. Chem. 84 [1972]1099/100; Angew. Chem. Intern. Ed. Eng!. 11 [1972] 1020). [11] Sidorov, L. N.; Borshchevsky [Borshchevskii], A. Ya.; Rudny [Rudnyi], E. B.; Butsky [Butskii] V. D. (Chem. Phys. 71 [1982]145/56, 146). [12] Parpiev, N. A.; Maslennikov, I. A.; Abdullaeva, Kh. S. (Uzbek. Khim. Zh. 17 No. 6 [1973]3/5; C.A. 80 [1974] No. 137605). [13] Maslennikov, I. A.; Parpiev, N. A. (Gidromet. Tsvet. Redk. Meta!. 1971156/61, 157/9; C.A. 76 [1972] No. 90849). [14] Ivanova, N. D.; Kladnitskaya, K. B. (Elektrodnye Protsessy Elektroosazhdenii Rastvorenii Met. 1978 30/4; C.A. 90 [1979] No. 111945). [15] Mattes, R.; Müller, G.; Becher, H. J. (Z. Anorg. Allgem. Chem. 389 [1972]177/87). [16] Dirand, J.; Ricard, L.; Weiss, R. (Transition Metal Chem. [Weinheim]1 [1975/76] 2/5). [17] Buslaev, Yu. A.; Shcherbakov, V. A. (Zh. Strukt. Khim. 7 [1966] 345/50; J. Struct. Chem. [USSR] 7 [1966] 332/6). [18] Karyakin, Yu. V.; Kryachko, E. N. (Zh. Neorgan. Khim. 12 [1967]2567/70; Russ. J. Inorg. Chem. 12 [1967]135517). [19] Marinina, L. K.; Rakov, E. G.; Gromov, B. V.; Minaev, V. A.; Kokanov, S. A. (Tr. Inst. Mosk. Khil!l. Tekhno!. Inst. No. 67 [1970] 83/6; C.A. 75 [1971] No. 83710). [20] Chakravorti, M. C.; Pandit, S. C. (Indian J. Chem. 9 [1971]1306/7). [21] Youinou, M.-T.; Petillon, F.; Guerchais, J. E. (Bul!. Soc. Chim. France 1968 503/7). [22] Pausewang, G.; Schmitt, R.; Dehnicke, K. (Z. Anorg. Allgem. Chem. 408 [1974]1/8). [23] Buslaev, Yu. A.; Petrosyants, S. P.; Tarasov, V. P. (Zh. Strukt. Khim. 11 [1970] 616/22; J. Struct. Chem. [USSR]11 [1970] 574/9). [24] Grandjean, D.; Weiss, R. (BulI. Soc. Chim. France 19673049/54). [25] Grandjean, D.; Weiss, R. (BulI. Soc. Chim. France 19673058/61). [26] Beuter, A.; Sawodny, W. (Z. Anorg. Allgem. Chem. 381 [1971]1/11). [27] Pinsker, G. Z.; Kuznetsov, V. G. (Kristallografiya 13 [1968] 74/9; Soviet Phys.-Cryst. 13 [1968] 56/9). [28] Sidorova, I. V.; Gusarov, A. V.; Gorokhov, L. N. (Intern. J. Mass Spectrom. Ion Phys. 31 [1979] 367/72, 372). [29] Karyakin, Yu. V.; Kryachko, E. N. (Tr. Voronezh. Tekhnol.lnst. 17 No. 1 [1968]110/4; C.A. 74 [1971] No. 35279). [30] Opalovskii, A. A.; Batsanov, S. S. (Zh. Neorgan. Khim. 13 [1968] 533/9; Russ. J. Inorg. Chem. 13 [1968] 278/82). [31] Mattes, R.; Müller, G.; Becher, H. J. (Z. Anorg. Allgem. Chem. 416 [1975] 256/62). [32] Opalovskii, A. A.; Kuznetsova, Z. M.; Batsanov, S. S. (lzv. Sibirsk. Otd. Akad. Nauk SSSR 1962 No. 9, pp. 46/53; C.A. 58 [1963] 6241). [33]' Kharitonov, Yu. Ya.; Buslaev, Yu. A.; Kuznetsova, A. A. (Zh. Neorgan. Khim. 11 [1966] 821/6; Russ. J. Inorg. Chem. 11 [1966] 445/8). [34] Opalovskii, A. A.; Batsanov, S. S. (Zh. Neorgan. Khim. 13 [1968] 2135/9; Russ. J. Inorg. Chem.13 [1968]1105/7). [35] Dehnicke, K.; Pausewang, G.; Rüdorff, W. (Z. Anorg. Allgem. Chem. 366 [1969]64/72, 70). [36] Pauling, L. (J. Am. Chem. Soc. 46 [1924] 2738/51, 2747). [37] Griffith, W. P.; Wickins, T. D. (J. Chem. Soc. A 1968 400/4). [38] lI'in, E. G.; Golovanov, B. V.; Ignatov, M. E.; Butskii, V. D.; Buslaev, Yu. A. (Dok!. Akad. NaukSSSR 276 [1984]612/5; Dok!. Chem. Proc. Acad. Sei. USSR 274/279 [1984]187/90). [39] Buslaev, Yu. A.; Kokunov, Yu. V.; Bochkareva, V. A.; Shustorovich, E. M. (Zh. Strukt. Khim. 13 [1972] 526/8; J. Struct. Chem. [USSR]13 [1972] 491/2). GmeLin Handbook Mo Suppt. Vol. B 5 232 MoLybdenurn Oxide Fluoride Ions [401 Ignatov, M. E.; lI'in, E. G.; GoLovanov, B. V.; Butskii, V. D.; BusLaev, Yu. A. (Dokl. Akad. Nauk SSSR 277 [1984]375/8; Dokl. Chern. Proc. Acad. Sci. USSR 274/279 [1984]236/8). [41] Mattes, R.; Mennernann, K.;JäckeL, N.; Rieskamp, H.; Brockrneyer, H.-J. (J. Less-Cornrnon Metals 76 [1980] 199/212). [42] Mattes, R.; Mennernann, K.; Rieskamp, H.; Brockrneyer, H.-J. (Chern. Uses MoLybdenurn Proc. 3rd Intern. Conf., Ann Arbor, Mich., 1979, pp. 28/33; C.A. 93 [1980] No. 85995). [43] Charninade, J. P.; Cervera-MarzaL, M.; Pouchard, M. (J. Cryst. Growth 66 [1984] 477/9). [44] Moutou, J.-M.; Charninade, J.-P.; Pouchard, M.; HagenmuLLer, P. (Rev. Chirn. MineraLe 23 [1986] 27/34). [45] Charninade, J. P.; Moutou, J. M.; VilLeneuve, G.; Couzi, M.; Pouchard, M.; HagenmuLLer, P. (J. SoLid State Chern. 65 [1986] 27/39, 34). [46] Atherton, M. J.; HoLLoway, J. H. (Chern. Cornrnun. 1978 254/5). [47] Beuter, A.; Sawodny, W. (Z. Anorg. ALLgern. Chern. 427 [1976] 37/44). [48] Geichrnan, J. R.; Srnith, E. A.; Swaney, L. R.; OgLe, P. R. (GAT-T-970 [1962]1/9; C.A. 61 [1964]12940). [49] BusLaev, Yu. A.; Petrosyants, S. P. (Zh. Neorgan. Khirn. 16 [1971]1330/6; Russ. J. Inorg. Chern. 16 [1971] 702/6). [50] BusLaev, Yu. A.; Davidovich, R. L. (Zh. Neorgan. Khirn. 13 [1968]1254/60; Russ. J. Inorg. Chern. 13 [1968] 656/60). [51] Griffith, W. P.; Wickins, T. D. (J. Chern. Soc. A 1967 675/9). [52] Marinina, L. K.; Rakov, E. G.; Bratishko, V. D.; Grornov, B. V.; Kokanov, S. A. (Zh. Neorgan. Khirn. 15 [1970] 3279/82; Russ. J. Inorg. Chern. 15 [1970] 1709/10). [53] Sergienko, V. S.; Porai-Koshits," M. A.; Khodashova, T. S. (Zh. Strukt. Khirn. 13 [1972] 461/7; J. Struct. Chern. [USSR]13 [1972] 431/6). [54] Chernyshov, B. N.; Shcherbakov, V. A. (Inorg. Nucl. Chern. H. H. Hyrnan Mern. Vol. 1976 127/9; C.A. 85 [1976] No. 131447). [55] BusLaev, Yu. A.; Kharitonov, Yu. Ya.; Davidovich, R. L. (Izv. Akad. Nauk SSSR Neorgan. MateriaLy 3 [1967] 589; Inorg. MateriaLs [USSR] 3 [1967] 527). [56] Ivanova, N. D.; KLadnitskaya, K. B. (Ukr. Khirn. Zh. 45 [1979]1061/4; Soviet Progr. Chern. 45 No. 11 [1979] 39/42). [57] Mattes, R.; MüLLer, G. (Naturwissenschaften 60 [1973] 550). [58] Pausewang, G.; Rüdorff, W. (Z. Anorg. ALLgern. Chern. 364 [1969] 69/87). [59] BusLaev, Yu. A.; Kokunov, Yu. V.; Bochkareva, V. A.; Shustorovich, E. M. (Zh. Neorgan. Khirn.17 [1972]3184/90; Russ. J. Inorg. Chern. 17 [1972]1675/8). [60] BusLaev, Yu. A.; Kokunov, Yu. V.; Bochkareva, V. A. (Zh. Neorgan. Khirn. 17 [1972]3377/8; Russ. J. Inorg. Chern. 17 [1972]1774/5). [61] BusLaev, Yu. A.; Kokunov, Yu. V.; Bochkareva, V. A.; Shustorovich, E. M. (Dokl. Akad. Nauk SSSR 201 [1971]355/8; Dokl. Chern. Proc. Acad. Sci. USSR 196/201 [1971]925/8). [62] HoLLoway, J. H.; SchrobiLgen, G. J. (Inorg. Chern. 20 [1981] 3363/8). Gmelin Handbook Mo Suppl. Vol. B 5 OxoperoxofLuoromolybdates(VI) 233 2.4.2.3 Oxoperoxofluoromolybdate(V1} Ions OIder data are given in "Molybdän", 1935, p. 153. Preparation, Formation. The formation of aseries of oxoperoxofLuoromolybdate(VI) species containing one or two peroxo groups and one to four fLuorine atoms was stated to occur in the reaction of oxofLuoromolybdates with H20 2 in aqueous solutions; e.g., in a solution of (NH4MMo02F4] at 7 wt% H20 2 concentration, MOO(02)Ft, MOO(02)F3H20-, and MOO(02hFH20- have been identified by the 19F NMR spectrum. In an aqueous HF solution of Mo02F2 (33 wt% Mo; F: Mo = 3:1) at 8.25 wt% H20 2 content the ionic species MOO(02)F~-, MOO(02)F3HP-, and MOO(02)F(H20)t were found. With increase in the H20 2 concentration the species with two and three F atoms decompose and part of the liberated HF goes towards the formation of the comparatively stable (at moderate H20 2 concentrations) MOO(02)F~-, wh ich is then converted into MOO(02hFH20-. This species is the predominant form in solutions with H20 2 concentrations >20 wt% [1]. In solutions containing 0.05 M Na2Mo04' 0.5 M H20 2, 0.0075 to 0.2025 M NaF, 1 M NH4N03, and acidified with HN03 to pH 0.5 at 25°C, the apparent formation constants of oxoperoxo fLuoromolybdate species containing 1, 2, 3, and 4 F atoms per molybdenum atom have been determined as"ß1 = 1.16x 104, "ß2=1.80x 107, "ß3=3.01 X 1010, and "ß4= 1.08 x 107, respectively. The method is based on potential measurements using a fLuorine selective electrode with an LaF3 membrane. The distributions of the molybdenum between the oxoperoxofLuoromolyb date species with different F: Mo ratio n as functions of the fluoride concentration are shown in Fig. 57. Changes in the H20 2 concentration in the range 0.1 to 1.0 moUL have no infLuence on the composition, indicating that the predominant oxoperoxofLuoromolybdate species in these solutions (n = 1 and 2) contain the same number of peroxo groups as the fLuorine-free species and can be formulated as MOO(02hFH20- and MOO(02hF~-. An increase in the acidity leads to an increase of the formation constant, the increase being more marked the greater the value of n. With increasing pH a rapid decrease of the concentration of the oxoperoxofLuoromolybdate ions in solution takes place. Even at an appreciable fluoride concentration practically no oxoperoxofLuoromolybdate ions are formed in solutions with high pH values, e. g., pH = 7 [2]. Fig.57. Distributions of molybdenum between oxoperoxo fLuoromolybdate ions with different F: Mo ratios (n) as func tions of the fluoride concentration, pF, in the solution [2]. In the solid state the species MOO(02)F~- and MOO(02hF~- have been isolated as alkali salts by reacting solutions of oxofLuoromolybdates with H20 2, see e.g. [3]. In the NHt-MoO~- -H20 2- HF-H20 system the most fLuoride-rich solid, (NH4bF[MoO(02)F4], appears at high fluoride con centration and low pH. At a somewhat lower fluoride concentration, (NH4MMoO(02hF2] forms. Recrystallization of this in hydrogen peroxide yields (NH 4b[F{MoO(02hFh] [8]. Gmelin Handbook Mo Suppl. Vol. B 5 234 MoLybdenum Oxide FLuoride Ions MOO(OJF~-. The IR spectrum of K2[MoO(02)F4]· H20 [3] and X-ray studies [4] show that the moLybdenum is seven-coordinated [3, 4]. The structure of the anion in crystaLLine K2[MoO(02)F4] · H20 is shown in Fig. 58. Its point symmetry is C1. This absence of symmetry is due to the environment of these ions, and more particuLarLy to the weak bonds formed by certain ° and F atoms with the H20 moLecuLes. The bond angLe of the Mo with the peroxo group 0(2)-Mo-O(3) is 43°30'. AdditionaL bond angLes are Listed in the paper [5]. For a comparative study of the structures of MOO(02)F~-, M002F~-, and MovOF~- in the correspond ing crystaLLine potassium saLt monohydrates see [6]. 0111 Fig. 58. Structure of the MOO(02)F~- anion in solid K2[MoO(02)F4]· H20 (interatomic distances in A) [5]. A crystaL structure determination of (NH 4bF[MoO(02)F4] shows the anion to have a pen tagonaL bipyramidaL arrangement with 0(1) and F(1) at the apices [9]. A reinvestigation of the structure yieLds the foLLowing interatomic distances: Mo-O(peroxo) = 1.903(5) to 1.917(5), MO--D = 1.670(5), Mo-Feq = 1.943(5) to 1.990(4), Mo-Fap = 2.070(4), O-Q(peroxo) = 1.434(8) A; the angLe of the peroxo group 0(2)-Mo-O(3) is 43.6(3t (eq = equatoriaL, ap = apicaL). For other distances and angLes at 250 and 290 K see the paper [10]. The 19F NMR spectrum of MOO(02)F~- (formed in a soLution containing (NH 4h[Mo02F4] and H20 2 in the moLe ratio 1:1 at - 20°C) shows chemicaL shifts löl of 472.0, 517.0, and 550.7 ppm apparentLy upfieLd with respect to F2 (values given in the text of [1]; different vaLues are given in a tabLe of [1] for the (equatoriaL) F atom FA in trans position to the peroxo group, for the two (equatoriaL) F atoms FBadjacent to and nearLy copLanarwith the peroxo group, and forthe axiaL F atom Fe in trans position to the MO=Ü group. The superhyperfine interaction constants J F- F are 130, 64, and 47 Hz for FA-FB, FA-Fe, and FB-Fe, respectiveLy [1]. The vibrationaL spectra in [11] obviousLy supersede those given in [3]. Infrared frequencies and Raman shifts (in cm-1) are observed and assigned as foLLows for K2[MoO(02)F4] (Raman intensities in parentheses) [11]: IR ...... 972 s 953 sh 876 w 856 s 597 vs 563 vs 501 vs Raman ...... 973(9) 958 sh 881(1/2) 601 (1) 568(8) 550(1 ) assignment ... v(MO=Ü) v(MO=Ü) v(O-Q) v(O-Q) vas(Mo02) vs(Mo02) v(MoF) v(MoF) IR ...... 378 357 337 m 274 vs Raman ...... 458(1 ) 412(2) 358(2) 337(10) 317(4) 263(w) assignment . .. v(MoF) ö(MoF) ? ö(MoF) ö(MoF) ö(MoF) ö(MO--D) From the strong IR band at 970 cm-1, the force constant for Mo=O has been estimated at 7.6 mdyn/A [5]. Gmelin Handbook Mo Suppl. Vol. B 5 OxoperoxofLuoromolybdates(VI) 235 MOO(OJ2~-' The structure of this anion has been determined by a crystal structure investigation of (NH 4MMoO(02hF2]. It shows a pentagonal bipyramidal arrangement with a point symmetry of almost Cs. Two side-on bonded peroxo groups and a fLuorine atom form the equatorial plane and one fLuorine atom and a double-bonded oxygen atom occupy the apical positions, see Fig. 59. Bond distances are Mo--O(peroxo) = 1.931 (2) to 1.976(2), MO=O = 1.688(2). Mo-Feq = 1.979(1), Mo-Fap = 2.199(1), O-O(peroxo) = 1.474(2) and 1.480(2) A; the angles of the peroxo groups O-Mo--O are 44.31 (6) and 44.65(7) (eq = equatorial, ap = api cal). For other distances and angles see the paper [12]. Fig. 59. Structure of the MOO(02)2F~- anion in solid (NH 4MMoO(02hF2] [12]. 19F NMR measurements of K2[MoO(02hF2]· H20 in aqueous solution confirm the nonequi valence of the two F atoms in the anion. The data are consistent with the structure found in the crystal structure determination of the ammonium salt. The spectrum shows one broad and one very broad line. The broader line is shifted toward lower applied fields with simultaneous narrowing of the less broad line when KF solution is added. The narrowing might be associ ated with fLuorine exchange between the complex and the solution. With respect to the exter nal reference F3CCOOH upfield shifts of löl = 58.6 and - 51.6 ppm [7] (recalculated with respect to F2: löl = 558.7 and 565.7 ppm [1]) resulted for the nonexchanging and the exchang ing F atoms, respectively [7]. The IR spectrum of K2[MoO(02hF2] recorded in [3] was reassigned in [11] as folIows: IR frequency in cm-1 938 vs 869 vs 854 vs 649 s 578 s assignment ...... v(Mo=ü) v(O-O) v(O-O) ? vas(Mo02) IR frequency in cm-1 535 s 518 vs 493 s 283 vs assignment ...... vs(Mo02) v(MoF) v(MoF) ö(Mo=ü) In addition, the Raman spectrum of (NH 4MMoO(02hF2] is given with shifts (in cm-1) and intensities (in parentheses) [11]: Raman shift 950(10) 875(6) 328(8) assignment ...... v(MO--o) v(O-O) ö(MoF) GmeLin Handbook Mo Suppl. Vol. B 5 236 Molybdenum Oxide Fluoride Ions F{MoO(02hFW. The structure of this anion has been determined by a crystal structure investigation of the yellow (NH4b[F{MoO(02)2Fh] at 170 and 290 K. The anion is composed of two identical (by symmetry) corner-sharing pentagonal bipyramids and has the point symme try C2; the twofold axis runs through the bridging fluorine atom. Two side-on bonded peroxo groups and a fluorine atom form the equatorial plane. The bridging fluorine atom and a double bonded oxygen atom occupy apical positions, see Fig. 60. Bond distances at 170 K: Mo--O(per oxo) = 1.934(2) to 1.972(2), MO=O= 1.670(2), Mo-Feq = 1.964(2), Mo-Fap = 2.196(1), O-Q(per oxo) = 1.473(2) to 1.487(2) A. Angles: Mo-Fap-Mo = 146.2(1)", Q-Mo--O of the peroxo groups are 44.29(8)" and 44.76(7)° (eq = equatorial, ap = apical). For other distances and angles see the paper [8]. 0(1) Fig. 60. Structure of the F{MoO(02)2FH- anion in solid (NH4b[F{MoO(02hFh] [8]. Water-Containing Species. The folLowing pentagonal-bi pyramidal species have been studied by 19F NMR. The numbering of the ligands is as folIows: L 1 for the axial-yl oxygen; L2 and L3 for the peroxo groups at the corners of the pentagen, L4 to L6 for the other corners (clock- or counter clockwise), and L7 for the ligand in trans position to MO--o. The following chemical shifts löl (with respect to F2; apparently upfield shifts) and superhyperfine interac tions J F- F are given [1]: formula ...... MOO(02)F(H20)t MOO(02)F(H20)t MOO(02)F2(HP)~O) L4 ...... F F L5 ...... F L6 H20 L7 ...... H20 H20 löl in ppm ...... 448.3 457.7, 502.8 J F- F in Hz ...... F4-F5: 136 formula ...... MOO(02)F3(H 20)- MOO(02)F3(H 20) L4 ...... F F L5 ...... F F L6 ...... F H20 L7 ...... H20 F löl in ppm ...... 462.0, 515.5 470.2,507.3, -557 J F- F in Hz ...... F4-F5= F6-F5: 138 F4-F5: 128, F5-F7: 68, F4-F7: 42 The chemical shift in the 19F NMR spectrum of MOO(02hF(H20)- with respect to F2 is (apparently upfield) löl = 568.0 ppm [1]. Gmelin Handbook Mo Suppl. Vol. B 5 OxoperoxofluoromoLybdates(VI) 237 References: [1] BusLaev, Yu. A.; Petrosyants, S. P.; Tarasov, V. P. (Zh. Strukt. Khim. 11 [1970] 616/22; J. Struct. Chem. [USSR]11 [1970] 574/9. [2] VoL'dman, G. M.; Vorob'eva, T. V. (Zh. Neorgan. Khim. 32 [1987] 67/70; Russ. J. Inorg. Chem. 32 [1987] 36/8). [3] Griffith, W. P. (J. Chem. Soc. 1964 5248/53). [4] Grandjean, D.; Weiss, R. (Compt. Rend. 261 [1965] 448/9). [5] Grandjean, D.; Weiss, R. (BuLL. Soc. Chim. France 19673044/9). [6] Grandjean, D.; Weiss, R. (BuLL. Soc. Chim. France 19673058/61). [7] Evans, D. F.; Griffith, W. P.; Pratt, L. (J. Chem. Soc. 1965 2182/4). [8] Stomberg, R. (J. Less-Common Metals 144 [1988]109/16). [9] Larking, 1.; Stomberg, R. (Acta Chem. Scand. 24 [1970] 2043/54). [10] Stomberg, R. (Acta Chem. Scand. A 42 [1988] 284/91). [11] Griffith, W. P.; Wickins, T. D. (J. Chem. Soc. A 1968 397/400). [12] Stomberg, R. (J. CrystaLLog. Spectrosc. Res. 18 [1988] 659/69). Gmelin Handbook Mo Suppl. Vol. B 5 238 Compounds Containing Mo, F, 0, and NobLe Gases 2.5 Compounds of Molybdenum with Fluorine, Oxygen, and Noble Gases 2.5.1 KrF2 • n MoOF4, n =1 to 3 The KrF2· n MoOF4 adducts can be prepared by reacting KrF2 with MoOF4 in S02CLF solution under anhydrous conditions at Low temperature. For the 1:1 adduct, ca. 0.3 9 of S02CLF is condensed onto ca. 0.10 9 of MoOF4 and a 25% excess of KrF4 is added at -196°C. The mixture is warmed to -80°C to effect reaction. The soLvent is removed at -48°C under vacuum. SoLutions of KrF2· n MoOF4 in S02ClF solvent are stable below O°C but can be briefly warmed to room temperature with no apparent decomposition. '9F NMR spectra have been measured at 84.66 MHz (spectraL width: 30 kHz) of soLutions in S02ClF at -121°C. These spectra indicate that KrF2 is fluorine bridged to the Mo atom, see structures I, 11, and 111. Observed moLe ratios of KrF2· n MoOF4 are as folIows: KrF2: MoOF4 .. 1.00 0.67 0.40 1:11:111 ...... 1.00:0.11:0.02 1.00:0.15:0.11 1.00:0.80:0.55 The resonances from the F nuclei on the (bridging) Mo'OF4 molecule of structure 111 severely overlap with those of Fe and F, of structure 11. The chemical shifts ö given in the tabLe on p. 239 are positive for frequency shifts which are positive with respect to '9F resonances of neat CCL3 F at -121°C. For KrF2·MoOF4 at -196°C, aRaman spectrum is plotted in the paper for shifts ranging from nearly zero to more than 1100 cm-'. The observed vibrationaL frequencies in cm-' and their intensities (given in parentheses) are assigned in the following tabLe that also indicates the approximate type of the vibrations: Raman shift (intensity) ...... 1034(12), 1025(33) 698(7), 691 (63) assignment, approximate description .. a" v(MO=Ü) a" v(sym in-pLane MoF4) Raman shift (intensity) ...... 702(5), 661 (2) 582(16) assignment,approximatedescription .. e,v(antisym in-plane MoF4) b" v(sym out-of-phase MoF4) Raman shift (intensity) ...... 462(59) 312(36) 260(1) 303(15) assignment,approximate description .. a" v(axial Mo-F) e, ö(MoOF4) b2, ö(MoF4) a" ö(MoF4) Gmelin Handbook Mo Suppl. Vol. B 5 239 Raman shift (intensity) ...... 226(7), 220(sh), 210(4) 174(sh) 155(8),140(8) assignment,approximate description .. e, ö(MoF4) b" ö(MoF4) e, ö(FMoF4) Raman shift (intensity) ...... 579(53),566(100) 479(40) 170(20) assignment, approximate description .. ~+, v(Kr-F) ~+, v(Kr-F) J't, ö(F-Kr-F) Raman shift (intensity) ...... 130(6), 116(2), 84(sh), 79(17), 72(15), 69(sh), 60(5), 52(30), 37(12), 29(6) assignment, approximate description .. Lattice modes species (structure) ö'9F J F- F in Hz FKrF-MoOF4 (I) Fa 70.4 Fa-Fb 296 Fb -12.4 Fb-Fe 44 Fe 148.6 Fa-Fb 314 Fa 64.9 Fb-Fd 48 Fb -28.8 Fb-Fe 52 Fe 150.1 Fb-Ff 44 Fd -34.8 Fe-Fd 44 Fe 190.8 Fd-Fe 92 Ff 208.5 Fd-Ff 110 Fe-Ff 100 FKrF-MoOF4(MoOF4h (1lI) Fa 65.4 Fa-Fb 326 Fb -31.1 Fb-Fe -50 Fe 150.5 Fd 14.6 Fe 0 Ff 0 Fg 10.8 HoLLoway, J. H.; SchrobiLgen, G. J. (lnorg. Chem. 20 [1981] 3363/8). 2.5.2 XeF2·nMoOF4, n=1 to 4 Preparation. XeF2· MoOF4 was prepared for the first time by reacting Mo02F2 with excess XeP2 in anhydrous HF, see p. 210 [2]. The 1:1 and 1:2 adducts can be produced by fusing stoichiometric mixtures of XeF2 and MoOF4 at 50 to 60°C. The cLear coLorLess Liquids crystaLLize at room temperature [1,3]. In S02CLF soLution at low temperatures, equiLibria invoLving higher chain-length species such as XeF2·nMoOF4, with n=3, 4, in addition to XeF2·MoOF4 and XeF2· 2 MoOF4 form when excess MoOF4 is added to solutions of the 1:1 or 1: 2 adducts [3]. XeF2· n MoOF4 was studied by '9F and 129Xe NMR using BrFs as solvent (for n = 1) or S02CIF. For the concentrations used, see [3, p. 2635]; also see [5]. XeF2 • MoOF4• In BrFs solvent, the 19F NMR spectra of F,Xebr' MoO(Fba)4 are first order, beLonging to the F,Fb,(Fba)4 spin system (t = terminal, br= bridge, ba = basaL). 129Xe sateLLites arising from spin-spin coupling of 129Xe with directly bonded fluorine nuclei are also observed. Gmelin Handbook Mo Suppl. Vol. B 5 240 Compounds Containing Mo, F, 0, and NobLe Gases The resuLts in BrFs soLution are consistent with free rotation about the Mo··· Fbr bond. The 129Xe NMR spectra beLong to the FbrF,F ba spin system. The observed fine structure (doubLet of doubLets) in these is consistent with an F-Xe-F group in which one fLuorine atom is bonded to the MoOF4 group. ALso the shifts ö toward higher frequency of the 129Xe resonances (see the tabLe with 129Xe NMR parameters, beLow) are consistent with enhanced XeF+ character of the adduct [3]. A "covalent" fLuorine bridged structure was aLso indicated by the isomer shift data in the 129Xe Mössbauer spectra of [4]. The foLLowing 19F NMR parameters (recorded obviousLy at 94.1 MHz) have been given for XeF2· MoOF4 (ö>O indicates shift in ppm toward higher frequencies referred to CCL3F at the sampLe temperature) [3]: in BrFs at - 84°C öC 9F) ...... -223.1{F,) -170.0{Fbr), +141.8{Fba) J{129Xe-19F) in Hz .. . 6140{F,) 5117{Fbr) JC9F-19F) in Hz .... . 264{Fc Fbr) 50{Fbr-Fba) in S02CLF at -124°C öC 9F) ...... -219.6{F,) -166.6{Fbr) +147.7{Fba) JC 29Xe-19F) in Hz .. . 6018{F,) 5110{Fbr) JC 9F-19F) in Hz .... . 267 and 262{F,-Fbr) 47 and 46{Fbr-Fba) The foLLowing 129Xe NMR parameters have been given for soLutions in BrFs at - 80°C and S02CLF at -118°C and measured by Fourier-transform spectra at 22.63 MHz [3]: öC 29Xe) ...... -1381 ppm -1441 ppm with respectto neat XeOF4 at 25°C J{129Xe-19Fx)inHz .5117{x=br) 5076 (x=br) 6139 (x=t) 6058 (x=t) remark ...... two doubLets two doubLets soLution ...... BrFs at -80°C S02CLF at -118°C Except for the öC 29Xe) vaLue wh ich was given as -1383 ppm in [5,6], the vaLues in the above tabLe agree with those in [5] and the data for BrFs soLutions given in [6]. 129Xe Mössbauer spectra (39.6 keV from Na3H2129IOs) indicate a quadrupoLe splitting of 40.3(6) mm/s. The observed isomer shift IS = 0.4(3) mm/s (with respect to centraL Xe in the cLathrate [3-hydroquinone) suggests a "covalent" F-Xe···F···MoOF4 structure [4]. The Raman spectrum of (the coLorLess, crystaLLized [3, p. 2639]) XeF2·MoOF4 at -100°C is plotted in paper [1] for shifts up to -1100 cm-1. The foLLowing shifts (in cm-1) and intensities (given in parentheses) have been found at -108°C and were assigned as foLLows [1]: Raman shift (intensity) ...... 1036(12), 1024(35) 698(8),689{47) 716(1),662{0.5) symmetry type ...... a1 a1 e approximate type of motion ... v{MO=O) (sym. in-pLane MoF 4) v{antisym. in-pLane MoF4) Raman shift (intensity) ...... 588(9) 546(3) 509{0.5) 466(12) symmetrytype ...... b1 a1 approximate type of motion ... v{sym. out-of-phase MoF 4) v{axiaL MoF) Raman shift (intensity) ...... 316(24) 307(10) 277(1), 251 (1) 212(2),204{2) 174(3) symmetry type ...... e a1 b2 e b1 approximate type of motion ... ö{MoOF4) ö{MoF4) ö{MoF4) ö{MoF4) ö{FMOF4) Raman shift (intensity) ...... 152{1 0), 136(5) 575(75), 566{1 00) 451 (16) 152(10) symmetry type ...... e L+ L+ approximate type of motion ... ö{FMoF4) v{Xe-F) v{Xe-F) ö{F-Xe-F) Gmelin Handbook Mo Suppl. Vol. B 5 241 Raman shift (intensity) ...... ; 119(9),74(5),55(18),46(17),39(14),31(16) symmetry type ...... - approximatetypeofmotion ... latticemodes The 152 cm-1 shift is attributed to both the F-Xe--F be nd and the F4Mo--F bend, wh ich are presumed to be cOincident [1]. XeF2·2MoOF4 • The 19F and 129Xe NMR spectra have been measured as described above for the n = 1 adduct [3]; for 129Xe NMR, also see [5]. The results suggest for the n = 2 species in S02ClF solution an analogous structure as for the corresponding Kr compound (Formula 11 on p. 238). The following 19F NMR parameters have been found in S02ClF at -124°C. Chemical shifts Ö are positive for shifts toward higher frequencies with respect to CCl3F at -124°C [3]: öC 9F) in ppm ..... -229.1(Fa), -167.1(Fb), +150.1(Fc)' -37.7(Fd), +195.1 (Fe)' +207.9(F,) J(129Xe--19F) in Hz .. 5197(Fa), 5110(Fb) JC9F-19F) in Hz .... 8(Fa-Fe and Fa-F,), 46(Fb-Fe), 47(Fc-Fd), 50(Fb-Fd), 100(Fd-Fe and Fd-F,), 102(Fe-F,) The following 129Xe NMR parameters have been found at -118°C in S02ClF solution. The chemical shift ö is positive for a shift toward higher frequencies with respect to neat XeOF 4 at 25°C [3, 5]: öC 29Xe)=-1338 ppm; JC 29Xe--19F) = 5036 Hz (doublet) and 6159 Hz (doublet). Of the colorless, crystallized [3, p. 2639] n = 2 adduct, Raman spectra have been recorded at -114°C for shifts up to -1100 cm-1 (plotted in [1]). Shifts, in cm-1, and intensities of the lines (given in parentheses) at -109°C were found and assigned as follows [1]: Raman shift (intensity) ...... 1039(43), 1030(20) approximate type of motion .... v(MO---Q) Raman shift (intensity) ...... 750(1), 734(6), 726(4), 715(37), 711 (sh), 700(20), 684(8), 669(8), 656(9), 593(7) approximate type of motion .... v(MoF4) Raman shift (intensity) ...... 575(100) 546(1), 528(2), 504(0.5) 422(9) approximate type of motion .... v(Xe--F) v(MoF4) v(Xe--F) Raman shift (intensity) ...... 388(1), 382(2), 324(sh), 314(20) approximate type of motion .... v(Mo--F), Ö(F4Mo=O) Raman shift (intensity) ...... 298(10), 276(1), 259(2), 236(6), 230(sh), 212(4), 198(2), 193(1), 170(1) approximate type of motion .... ö(MoF4) Raman shift (intensity) ...... 156(10) 142(4) 111(3),99(2),68(12) approximate type of motion .... ö(F-Xe--F)ö(F4Mo--F) Ö(Mo--F-Mo), torsional and lattice modes XeF2·3MoOF4• For this adduct, a structure analogous to the corresponding Kr compound (see Formula III on p. 238) has been derived from 19F and 129Xe NMR spectra recorded as described for the n = 1 adduct [3] above; for 129Xe NMR data, also see [5]. The sign convention for the chemical shifts Ö is as given for n = 1 and n = 2, above. In S02ClF at -124°C the following 19F NMR parameters have been given [3]: öC 9F) in ppm ...... - 230.4(F.), -167(Fb), + 150(Fc)' - 28.9(Fd), - 62.8(Fg) with respect to CCl3F at -124°C JC 29Xe--19F) in Hz .... 6210(Fa),5110(Fb) JC 9F-19F), in Hz 47(Fc-Fg), 50(Fb-Fd, Fb-Fe, and Fb-F,), 266(Fa-Fb) Gmelin Handbook Mo Suppl. VO,l. B 5 16 242 Compounds Containing Mo, F, 0, and NobLe Gases The foLLowing 129Xe NMR parameters have been found with S02CLF soLutions at -118°C [3,5): öC 29Xe)= -1321 ppm with respect to neat XeOF4 at 25°C JC 29Xe-19F) = 5029 Hz (doubLet) and 6156 Hz (doubLet). XeF2 ·4MoOF4• This adduct has been characterized by 19F NMR in S02CLF soLution at -124°C and the foLLowing structure was derived. The chemicaL shift öC 9F) refers to CCL3F at -124°C and is positive for shifts toward higher frequencies. The foLLowing 19F NMR parameters are given in (3): öC9F) in ppm: -230.8{F.), -167(Fb), +150(Fc)' -29(Fd), -64.9(Fg), -55.2(Fh) JC 29Xe-19F) = 6200(F.) and 5000 Hz (Fb) JC 9F-19F) =48 Hz (Fc-Fg) and 258 Hz (F.-Fb). Chemical Reactions. The soLid compounds are stabLe at ambient temperature in a dry atmosphere (4). DissoLution of XeF2·2MoOF4 or mixtures of the 1:2 adduct and MoOF4 in BrFs Lead to rapid decomposition to MoFs and presumabLy BrOF3 and Br02F. In HS03F soLvent the XeF2· MoOF4 undergoes soLvoLysis at -80°C according to XeF2· MoOF4 + HS03F --> FXeO(O)S (F)OMoOF4 +HF; FXeO(0)S(F)OMoOF4 ;;:::=: FXeOS02F + MoOF4. Both XeF2·MoOF4 and XeF2 ·2MoOF4 are easiLy soLubLe in S02CLF at Low temperatures (3). References: (1) HoLLoway, J. H.; SchrobiLgen, G. J. (Inorg. Chem. 20 (1981) 3363/8). (2) Atherton, M. J.; HoLLoway, J. H. (Chem. Commun. 1978254/5). (3) HoLLoway, J. H.; SchrobiLgen, G. J. (Inorg. Chem. 19 (1980) 2632/40). (4) DeWaard, H.; Bukshpan, S.; SchrobiLgen, G. J.; HoLLoway, J. H.; Martin, D. (J. Chem. Phys. 70 (1979) 3247/53). (5) SchrobiLgen, G. J.; HoLLoway, J. H.; Granger, P.; Brevard, C. (Inorg. Chem. 17 (1978)980/7). (6) HoLLoway, J. H.; SchrobiLgen, G. J.; Granger, P.; Brevard, C. (Compt. Rend. C 282 (1976) 519/21 ). Gmelin Handbook Mo Suppl. Vol. B 5 Compounds Containing Mo, F, and N 243 2.6 Compounds of Molybdenum Containing Fluorine and Nitrogen 2.6.1 MoF5N3 and MoF4(N3h The reaction of tri methyl silylazide, Si{CH3hN3 , with excess MoF6 in C2Cl3F3 (Genetron 113) as solvent at low temperatures gives a yellow solid, assumed to be MoF5N3, wh ich decomposes at -10°C [1]. In the reaction product obtained at -70°C a doublet and quintuplet was found in the fluorine resonance spectrum from MoF5N3 (ö = 182.4 and 237.6 ppm, J = 94.4 Hz) and a pair of triplets from cis-MoF4{N3b (ö= 147.1 and 179.0 ppm, J = 91.1 Hz; chemicaL shifts, positive to low field, are referenced to CCl3F as internal standard) [2]. Adducts of molybdenum fluorides and oxide fluorides with NO, such as {NO)MoF6, (NO) MoOF5, {NObMoOF6, {NO)M020 2Fg (see, e. g. p. 171), will be described in a voLume dealing with the coordination compounds. References: [1] Fawcett, J.; Peacock, R. D.; RusselI, D. R. (J. Chem. Soc. Dalton Trans. 1980 2294/6). [2] Glavincevski, B.; Brownstein, S. (Inorg. Chem. 20 [1981] 3580/1). Gmelin Handbook Mo Suppl. Vol. B 5 16'