A Thesis Submitted by COLIN JAMES LYNE LOCK, B.Sc., A.RX.S. for The

baAE COORDINATION COMPOUNDS OF RHENIUM.

A Thesis submitted by

COLIN JAMES LYNE LOCK, B.Sc., A.RX.S.

for the Degree of

Doctor of Philosophy of the

University of London.

July, 1963. Royal College of Science South Kensington, S.W.7. To Helen, Nicola and Allison who hindered rather than helped, but who made it worthwhile. It is more laborious to accumulate facts than to reason concerning them; but one good experiment is of more value than the ingenuity of a brain like Newton's. Sir Humphrey Davy.

Refrain from illusions, insist on work and not on words. Patiently search divine and scientific truth. Mendeleev t s Mother. Acknowledgements.

I mould like to thank Professor G. Wilkinson for his encouragement, criticism and advice during his supervision of this work. My thanks are also due to Dr. L. Pratt for advice on nuclear magnetic resonance techniques, Dr. J. Wood for advice on infra-red spectroscopy, and Dr. W. P. Griffith for general discussion and biscuits. I would like to thank my colleagues, especially N. P. Johnson, R. Gillard, Dr. A. Davison, and Dr. J. McCleverty for their advice and company. Finally I am indebted to my wife who typed this thesis and who has had to suffer Rhenium Chemistry for the past three years. CONTENTS.

Chapter Title Page

Abstract 1. Introduction 1 2. Phosphina complexes 15 3. Analysis of cyanide in. cyanide complexes 30 4. Cyanide comp la xo 38 5. Dioxo-complexes of rhenium 52 6. 2:4-propanedione complexes 60 7. Oxides of rhenium 65 8. Experimental 73 9. Appendix 104 10. References 105 Abstract.

Two compounds previously described as trichlorobis(triphenylphosphine)rhenium(III) have been shown to be trichlorobis(triphenylphosphine oxide)rhenium(III) and oxotrichlorobis(triphenylphosphine)rhenium(V). Other phosphine complexes of Re(III) and Re(II) prepared in a similar manner to the latter have been shown to be compounds of Re(V). A new arsine complex of Re(V) and other arsine and arsine oxide complexes of rhenium(III) have been prepared. A triphenylphosphine complex of Re(II) has been prepared. Previously reported cyanide complexes of Re(VI) and Re(V) have been confirmed, although the purification procedure described for the latter causes hydrolysis of the compound. The supposed purple hydroxocyanide complex of Re(VII) has been shown to be the oxohydroxocyanide complex of_Re(V),- as have previously reported purple salts of the dioxotetracyanorhenate(V) have also been shown to be salts of this anion. The first transition metal- nitridocyanide complex has been prepared. A new method of preparing potassium dioxotetracyanorhenate(V) is described. It has been shown that the diagnostic region for M=0 infra-red stretching frequencies must be extended -1 from 900 cm. down to at least 780 cm.-1 where a linear 04\1=0 group exists in an octahedral complex. Stable phases Re205 and Re308 have been prepared by the oxidation of rhenium dioxide hydrate. The former is a mixture of Re0 3 and an unidentified oxide. The latter does not contain any Re03. Mixed phosphine 2:4-propanedione complexes of rhenium(V) and rhenium(III) have been prepared. 1. 1. INTRODUCTION. Rhenium has been anelemont of chemical con- troversy since its discovery was first claimed by Noddack2 Tacke2 and Berg in 1925 (1). Th3 validity of this claim has been challenged, particularly by Druce (2) and Prandtl (3). The work of Noddack appears doubtful because he claimed to have isolated both technetium and rhenium in macro-quantities from certain platinum ores and columbite. Since that time all attempts to isolate naturally occurring technetium (all isotopes of which are radioactive) in macro-quantities have been unsuccessful (4). Prandtl (3) was also unable to isolate any rhenium from the columbite ore and Russian workers could not find rhenium in the platinum ores (52 6). Later, and independently, Loring and Druce (728) isolated the element from pyrolusite and molybdenum glance, and this was later confirmed by other workers (2). Probably Druce and Loring should be credited with the actual discovery of rhenium. The Noddacks (92 10)2 however, were certainly the first workers to isolate the element in any quantity and to prepare a number of chemical com- pounds2 and their name for the element has been retained. The chemistry of rhenium is complicated for a number of reasons. Compounds have been prepared in all the formal valency states from Re(-1) through Re(7)2 and 2. coordination numbers of , 4 through 8 have been characterised, arid even a coordination number of 9 has been claimed. Examples of these compounds are given in Table 1. Rhenium also shows a remarkable ability to bond strongly to groups such as -H, =02 -OH, ;1\12 and -OMe, which, because many of the compounds of rhenium are stabilised by organic ligands with high molecular weight, have not been detected analytically. It is only with the advent of modern techniques such as infra-red and nuclear magnetic resonance spectroscopy that these groups have been detected. One other difficulty that has boon en- countered is that the presence of impurities apparently affects the course of reaction of rhenium metal. It was shown by Colton (11) that very pure rhenium metal gave hexachlororhenium(VI) on chlorination whereas the com- mercial metal gave pentachlororhenium(V). This has also been observed by us and in fact the formation of ReC1 is 6 a good indication of the purity of the metal. In the initial stages of this work the rhenium metal available contained z,,,/1,5% potassium salts and gave onlyReC1,) (<1% ReC16) on chlorination. The latest batch of com- mercial metal made by the hydrogen reduction of ammonium perrhenate and claimed to be 99.9% pure gavei\-/10 RoC16 on chlorination. A result of these effects is that many papers

3 Table 1 The different valen0 states and coordination numbers of rhenium in its compounds.

Formal valency Compound Coordi- Compound of rhenium nation Number -1 NaRe(00) (12) 4 ReC14 (26) 5 (Ph3P) 2RoI + 2 Roo(c0)10 (13) (Ph3 P2 Fo(Co) 4 (14) 5 (Ph3P0) 2ReC13 + (Ph3P) 211eNC12 (27) 0 K Re(CN) (15) 5 6 6 (Ph3P),Re0C1-4 + (Ph,P),JleI (Repy402)C1 '+(28) 2 2 L-)Reel22 (16) 3 Re2C16, (17) 7 (Ph:AP)4ReHR (29) +(18)

L is the chelating ligand o-phenylenebis(dimethylarsine)i + This work. 4. on the chemistry of rhenium are at least partly inaccurate. Before any new experiments could be started it ti as usually necessary to investigate the starting product, and in some cases to reformulate the reactions and compounds. The chemistry of rhenium has been reviewed exten- sively recently (309 329 339 349 35)9 but little attention has been paid to the coordination chemistry of rhenium apart from in Nyholm's reviem.(30) A general review of the coordination complexes of rhenium will be made hare, except for some phosphine complexes and the cyanides which will be treated more fully in the chapters on the new work on these complexes. Rhenium(-11 The only complex of rhenium mith a formal valency of (-I) which has been substantiated is NaRe(C0)5. (12) Polarogrephic reduction of the perrhenate ion (36) suggested that the rhenide ion Re(-I)- existed, and salts supposed to be rhenides mere isolated (37). Colton et al. (38) have also shown that polarographic reduction of a number of rhenium compounds gave products which, from the number of electrons in the reduction, are compounds of Re(-I). Homover, it mas shown by nuclear magnetic resonance studies of the reduced solutions that Re-H bonds were present and subsequently it has been suggested that the so-called rhenides are hydrides of 5. the type KRo 111114.2H20 (39) or Dc.2Rovill82 (40). From the disagreement that still exists this matter is probably not yet finally settled. Rho nium(0) Rhenium(0) occurs in the dimcric carbonyl Ro2(CO) (13) mhich contains a metal - metal bond (41). 10 By analogy with carbon in ethane this might be regarded as a compound of Ra(I). True Ro(0), however, occurs in the monomeric complex (Ph3P)2Re(C0)4 (14). Rhcnium(I) This formal state exists in a number of compounds. There are many types of carbonyl complex such as the hydride HRe(C0)5 (12), cyanide Do(C0)4(CN)a (43),halides, both monomeric Ro(C0)5X (X = Cl, Br, I) (44), and dimerictlie(C0)1X2(45) with halide bridges. A number of substituted carbonyls of the typo L2Ro(C0)3X (L = py9 Ph3P, 2(o-phon), aniline) (43,45) have boon prepared, as has the bridged hydroxocarbonyl compound K[SCO)4R0 e(C0)4y and a similar thio-compound (C0)4Re Re(C0)4 (46). Other carbonyl complexes are of the type Die(C0)4L21C1 (L = CN.C61-14.CH3, NH3, and PPh3) (43,47). Other salts containing Re(I) in the cation have been prepared recently. They are isocyanides of the type Pie(CH3C6H4NC)d+ (48), the carbonyl [!to(C0)61A1C14 (49) and the diethylcnc carbonyl ble(C0)4(C2H4)21+ (50) and the arena sandwich complexes 6. of the typo [RciAr 1+ (Ar = benzene or mesitylene) (51). 2 Diamagnetic compounds of Re(I) have been prepared by the reaction of halide complexes of Re (ITT) and acetylenes (52)5 for example; RoCl(Ph.C.;CH)5 ReLa(HOGH(CH3)CH2C=0H2), and ReC1.(Ph P)(HOCH(CH )CH T=ICH) 3 3 2 2' Rhenium(II) This must be considered as one of the rarest valency states of rhenium. The only complexes which have definitely boon identified in this valency state are those made from the bridging arsines (16) and phes- phines (53) Ro2L2X2 (X = Cl, Br, I; L = o-phonylonebis- dimethylarsino or ethylene-bis(diphonylphosphine).). Diamagnetic complexes of the type CRe(PR3)2(RNC)I3I- have been reported (54)5 but Nyholm (30) suggested this should be formulated L*(PR3)4(RNC)214- (eI1-4H As the starting product has boon shown to be incorrectly formulated (21) this work must remain questionable until chocked. Phosphinc complexes of the type (R3P)2R0X2 (X = Cl, Br, I) have twice been claimed in the literature (535 55) but both have boon reformulated as compounds of Re(V), the former as (R P) RoOX (0Et) (21)5 and the 3 2 2 latter as (R,P) ReNC1 (27). The first true complex of -) 2 2 the typo (R P)ReI is described in this mork. 3 2 2 Claims have been made by Russian 'workers (56) to have prepared halogen complexes of Re(II) by hydrogen 7. reduction of trichlororhonium(III) in hydrochloric acid. This work is far from satisfactory, and preliminary work in this laboratory has shown that similar salts can be made without any reduction. This work must be considered suspect until checking is complete.

Until recently Re(III) was the most common valency of rhenium in coordination compounds, a groat variety of compounds having been prepared. Despite the great number of compounds, at present very little is known of the stereochemistry of Re(III). Most of the compounds have boon prepared by the direct addition of the ligand to trichlororhenium(III). Compounds of the typo (ReC1 L) have boon 3 n prepared in large numbers (L = C1- (57), PPh3, py (18), As0 (this work) OH H OH (58), PPh30 Ph3As1 Ph3 ' C2 H5 ' C3 7 PEt Ph (53), and RNC (63).). All these compounds are 2 at least dimoric and possibly polymeric. Crystal structure studios have shown that ReC1 is trimeric 4 (59,60) and the rhenium is seven coordinate (see Figure 1), but Cotton's suggestion that all these compounds are of similar type (60) has not been substantiated. Molecular weight measurements have shown (ReC1 PPh ) is dimoric 3 3 n in non-coordinating solvents.

Some other compounds of the type (ReC13L) U. The structure of Reg 9. (L = 1:2 dimethylthioethano, o-phenanthrolino, 2,2'- dipyridyl (18) ) are probably related to the second type of compound ReC13L2 (L = H2O (61), RCO2H (62), Ph3P0

(this work), and py (18)). The solids are readily soluble in many organic solvents and, by analogy with

(Ph PO) ReC1 are presumably all monomeric and thus 3 2 35 five coordinate. The trigonal bypyramidal structure has boon proposed for these compounds (18) but has not boon substantiatod.

Another type of trichlororhonium(III) adduct is RoC13L which has been prepared only recently. (L = 3 PEt2Ph or L3 = PEIfh C2H4(PPh2)2) (53). Other complexes of the same type have been made by reacting potassium haxaiodorhenate(IV) and organic phosphites, the product being Ra1 ((Ro) P) (63). A further series 3 3 3 of compounds, probably related to the first typo, is formulated Re c1L =o<-picolino, 2,6-lutidine, tri- 2 ethylenetutramine, 2-vinyl-pyridine) (18). The same workers found that under identical reaction conditions other ligands gave compounds of the typo Ro2C15L = quinaldine) and Re2C141, (L = o-phenanthroline, 2,2'- dipyridy15 4-methyldithioveratrole) but nothing is known of the structure or mhother in fact these are compounds of Re(III).

Russian workers have prepared ammines of the typo Ro(am)4C13 (64) claiming'four - coordinated Rc(III). 10. Nyholm (30) has suggested that these arc really six co-

ordinate species of the typo LRe(am)ci 1C1. This mould 2 be similar to the arsine adducts already prepared by Nyholm ERe(diarsine) Cl IC10 (16) and Venanzi [ke(tetra- 2 2 4 arsine oxide)C1 ]Cl (65). 2 Taha (62) has prepared carboxylate derivatives

of Re(III) of the type [Re(RCO2)2C1l2 with bridging carboxylate groups. The carbamate compounds of the type

ReC12(NR2CS2) (R = methyl, ethyl, butyl) have also boon prepared. (66)

Compounds of Re(III) which contain no halogen

are tris(2:4-propanedionato)rhenium(III) (52), the alkoxides, such as Re(OMe)3 (58), and the alkyls, such as Re(Me) (67), although more recent attempts to prepare 3 the alkyls have been unsuccessful (68,69). Attempts to prepare a cyclopentadione compound of rhenium analogous

to ferrocene gave the interesting compound (A-C H ) ReH 5 5 2 which may be regarded as a compound of Re(III). This compound is as strong a base as ammonia and can be readily

protonated to give the cation ("1-05H5)2Re112+ (70). Other hydrides of Re(III) have been prepared by the reduction

of oxotrichlorobis(triphenylphosphine)rhonium(V) with

sodium borohydride (29). They arc seven - coordinate

Re113(PPh3)2.2C2H50H and Re1-13(PPh3)4 and presumably have the same structure as the seven - coordinate Moll complexes of the typo E-Mo(diarsine)(CO) Br 1° (30). 3 2J 11. Rhenium(IV) Although Re(IV) has boon considered as one of the more stable valoncies of rhenium (72), because of the tendency of Re(V) and Re(VI) aqueous solutions to disproportionate to Re (IV) and Re(VII), the number of coordination-compounds prepared so far is not very large. This may be because until fairly recently the tetra- halides have not boon available as starting products. Most of the known complexes of Re(IV) have boon prepared in aqueous solution. The most widely known are the halides, RoX62- (X = F (73), C1(19), Br (74), I (75)), the hydroxohalides, [!ie(OH)q 2 (X = Cl (76,77), Br (78)), and the oxygen bridged chloride eC15Re0ReClj4- (76277). This last compound is interesting as, if it has similar bonding to the ruthenium ana- logue EC15Ru0RuCl5i (79), it should contain one unpaired electron per rhenium atom; but the compound is practically diamagnetic, so there must be extensive metal - metal interaction across the oxygen bridge. Numerous salts, both inorganic (72,80) and organic (81, 82,83), have been prepared from these ions. Analogous Re(SCN) have also been prepared thiocyanate salts M2 6 (76,84). Dipyridinium hexachlororhenate(IV) has been a starting product for another type of rhenium(IV) compound. On heating, this compound eliminates hydrogen 12.

chloride giving py2ReC14 (85). A number of compounds of the typo ReX4L2 (X = Cl, Br, I; L = PPh3, py, PEt2Ph) have boon prepared by several different methods (18,53,

71), and doubtless this list will be extended consider- ably in the future. Other complexes which have boon prepared in

aqueous solution are oxalates. Reaction of oxalic acid

with rhenium dioxide slowly gives HN(OH)3.C204.H20]

which is in equilibrium with the di-acid form H2[Re(OH)4.C203. Alkali salts of the acids have boon claimed (86). The

salts of the latter acid are diamagnetic and have boon postulated as dimeric mith a metal - metal bond. These

compounds are easily hydrolysed by bases giving Re02.X1120. The same salts have apparently been prepared by other workers (87). They have reformulated the salts as di- merle, containing an oxygen bridge, analogous to the

chloro-complex, viz: Kit OH)3C204Re-O-ReC204(OH)3] and

K4 1OH(C204)2Re-O-Re(C204)201q. The acid of the latter salt has been prepared. Somewhat similar types of compounds have been prepared with catechol, Hgle(OH)3C0402H203

and gallic acid, H2[Re(1120)2(C6H202.0H.0O2)21.6H20. Salts of these compounds have also been isolated (88,89).

A seven - coordinate compound of Re(IV) is

the hydride Re114(PPy3.(7l). Taha has also prepared

compounds such as Re2C14(RCO2)2.(OH)2 in which the 13. rhenium is claimed to be seven - coordinate. Those compounds have bridging hydroxo- and carboxylato- groups and a metal - metal bond. Similar compounds, but having bridging oxo- and carboxylato- groups and a metal - metal bond, are complexes of the type Re 0 Cl (RCO ) (62). 2 2 2 2 2 Rhenium(V) At the beginning of this work the number of complex compounds of Re(V) was small. Now the number known is greater than for any other valency state of rhenium. As many of the new discoveries will be discussed more fully in later chapters only a brief resumd of earlier compounds will be made. The chloro-complex DeOC15 1 2has been known for a considerable time (90) as has the oxocyanide le02(CN)14,]3" (91). Other oxo-complexes of the type Re02L4 (n, positive or negative, L, unidentato or half bidentate ligand) have been prepared for biguanidine (92), diphenylcarbazone (93), dithiocarbamic acid (94), thiocyanate (95), pyridine (28), and ethylanodiaminc (95). An eight coordinate cyanide, K Re(0N) has been prepared 3 8 (31), and other eight coordinate species arc salts of the diarsine complexes fac(diarsine)2X43+ (X = Cl, Br) (97). An interesting seven - coordinate rhenium(V) compound is the ion [(Re(diarsine)2C12)26]4+ (97), and this coordination number is also found in the hydride RoH (PPh ) (71). 5 3 2 14. Rhenium(VI) The only coordinatiun compounds of this valency state known aro the fluorides, M ReF and MRoF7 (98); and 2 8 the cyanide M2Rc(CN)8 (31). Rhonium(VII) No coordination complexes of Re(VII) aro known. 15. PHOSPHINE COMkLEXES. Two compounds, formulated as trichlorobis(triphonylphosphine)rhenium(III), have boon described in the litoraturo; a rod compound by Colton ct al. (18) and a yollow ono by Frcni and Valenti (55). It has boon shown by us (21) and independontly by Chatt and Rome (53,99) that both these compounds wore incorrectly formulated; they both contained oxygen. Colton's compound was shown to be trichlorobis(triphenylphosphine oxide)rhonium(III), and that of Froni and Valenti, oxotrichlorobis(triphonylphosphine)rhenium(V). It was not possible at that time to obtain reliable oxygen analyses in the presence of phosphorus by the method used (100), and the prosence of oxygen was inferred from an examination of the infra- red spectra. 6ubsequently confirmatory evidence was obtained. Attempts to prepare genuine trichlorobis(triphenylphosphinc)rhunium(III) by a number of methods ware unsuccessful and it is doubtful whether this compound exists. The spectrum of Coltun's compound showed it to bo a complex of triphenylphosphine oxide. A.band charac- cotd& toristic of coordinated triphenylphosphinck4as observed -1 at 1125 cm. A further very strong band was observed -1 at 720 cm.-1 in addition to the two bands at 685 cm. -1 and 740 cm, which also occur in triphenylphosphino 16. complexes. The compound was shown not to be a mixed phosphinc - phosphine oxide complex, as the band at 1090 -1 cm. characteristic of triphenylphosphine was missing. -1 No bands were observed in the regions 3100 cm. and 780-1000 cm.-1, showing that =0, -OH, and OH2 groups more absont. On the basis of the spectra and the analyses the compound was reformulated as trichlorobis(tri- phanylphosphinc oxido)rhenium(III). Subsequently trichloro(triphenylphosphino oxida)rhenium(III) (in good yield) and trichlorobis(triphenylphosphinc oxide)rhanium- (III) (in poor yield) were made by the direct interaction of triphenylphosphino oxide and hexachlorodirhanium(III) in acetone. The infra-rod spectra of those compounds were identical with that of Colton's compound. Colton proposed a reaction scheme Ph3P (Ph P IC1 ) Ph P RoC1 .(Ph P) ReC1 --4(Ph P) ReC1 3 n 2 3 2 ci2 (A,3 unstable)(B, 3 unstable)2 4 3 3 Both the intermediates have now been preparod (A, this work, B, sue ref. 29) and haves been shown to be stable compounds. A more probable mechanism involves the chlorination of the phosphine and subsequent hydrolysis to phosphinc oxide, a reaction which is well known (101). The hydrolysis might occur by reaction with acetone. Colton stated that the reaction was complete in thirty minutes. We found that in acetone dried with molecular sieve, with no other precautions, complete reaction took 17. up to fourteen hours. Howovor, the addition of a few drops of water shortened tho reaction time to a few minutos. Possibly the acotono used by Colton was mot. It was not possible to decide ,why this reaction gave good yields of the bis-phosphinc oxido complex, when direct reaction of triphenylphosphinc oxide with hexa-

chlorodirhonium(III) gave very poor yields of the bis- phosphine oxide complox. Trichlorobis(triphenylphosphine oxido)rhenium- (III) was monomeric, diamagnetic and fairly soluble in organic solvents, similar to othor bis-addition products of trichlororhenium(III) (62), but unlike mono-addition products, which, if they wore soluble, were at least dincric in non-coordinating solvents. As the compound was monomoric the rhenium atom must be fivo coordinate. Colton et al. (18) have shown that the structure must be trigonal bipyramidal rather than square pyramidal, since ligand field calculations have shown that only the former would give a diamagnetic complox (80). The yollow compound describod by Froni and Valenti could have boon any of a dozen compounds on tho basis of the analytical results. All those possibili- tios, except uxotrichlorobis(tri,lhonylphosphine)rhonium- (V), could be eliminated by examination of the infra-red

spectrum. This was almost identical to that of tri- 18. chloro(triphonylphosphino)rhenium(III) except for a very strong band at 969 cm.-1 which is in the region where M=0 stretching frequencies are found (102). No 0-H or OH frequencies wore observed, nur P-H (2400 cm.-1 2 ) or -1 1)=0 (1125 cm. ) strotching froquuncies. It was not possible to confirm the above formulation; however, oxotrichlorobis(tripheaylarsinc)rhenium(V) was prepared by a similar method and it was possible to show the presence of oxygen in this compound analytically. The infra-red spectrum was vary similar, the.Re=0 strotching frequency being at 967 cm.-1 The arsine complex was much less stable than the phoshinc complex, decomposing in boiling ethanol.

Further ovidunce was available to show that the formulation of the phosphine compleX was corroct. The compound was diamagnetic, and derivatives obtained by reaction with various reagents (pyridine, ethanol, potassium cyanide, 2:4-propanedione, ethyl nediamine) more all compounds of Re(V). As none of thesc reagents normally acts as an oxidising agent it seems probable that the starting product contained Re(V). It was im- possible to prepare the compound by the direct interaction of triphenylphosphine and hoxachlorodirhonium(III) as mould be expected if Froni and Valontits original formulation were corroct. HomGvor, an old sample: of hoxachlorodirhenium(III) which was allowed to stand in 19. laboratory air, when extracted with acetone gave a green solution This solution, when separated immediately and treated with triphonylphospnine, gave the desired product. The residual hexachlorodirhonium(III) dissolved slowly in acetone giving a red solution. An identical green solution was obtained when a solution of penta- chlororhunium(V) in acetone was allowed to stand in moist air. This g;ave the same reaction with triphenylphosphine. Probably the gran solution contained the unknown oxotrichlororheniun(V), but it was not possible to isolate it. Reaction of triphonylphosphine and pentachlororhonium(V) in dichloromothanc or dry acetone gave a dirty green, weakly paramagnetic substance ckkeff = 1.2 B.M. at 298°K), which was tctrachloro(triphonylphosphinc)rhenium(IV). Thu substance was apparently polymeric, being insoluble in all thu common solvents. Attempts were made to oxidise hexachlorodirhonium(III) and trichloro(triphenylphosphine)rhenium- (III) under controlled conditions. No reaction was observed when dry oxygen was bubbled through boiling acetone and diethyl other solutions of hexachlorodirhonium- (III). The action of oxygen on trichloro(triphenylphosphino)rhunium(III) in boiling acetone solution gave par- tial conversion to trichloro(triphenylphosphinc oxide)- rheninm(III) after 48 hrs. 20. Three possible isomers of (Py)2Re0C13 can exist and those are shown in Figure 2. Three isomers have been prepared (two in this work and one by Johnson (103)) but it was not possible to assign structures to the compounds. Only one isomer was prepared by reaction A in Figure 3. This isomer was yellow. It has been shown (104) that the yellow-green isomer of oxotrichlorobis(phonyldiethylphosphine)rhenium(V) similarly prepared has the structure equivalent to 112 and it was assumed that this also applied to the triphenylphosphine compound. The other isomer prepared in this work was green and had an Re-0 stretching frequency of 982 cm.-1, whereas the isomer prepared by Johnson was yellow-brown and had an Re=0 stretching frequency of 981 cm.-1 As Froni and Valenti (55) had prepared a number of compounds supposed to contain Re(II) and Re(III) by methods similar to that used to prepare isomer A above, all these reactions were examined. In fact all the compounds contained Re(V). The supposed reactions of Frani and Valenti arc summarised in Figure 3a, with our re- formulation in Figure 3b, together with such extensions in the reactions as MG have made. Only for the chloride was the oxotrihalido prepared directly from perrhenic acid, and oven in this case, if insufficient acid was present the compound vas Figure 2. Isomors of (Ph3 21. E1 2-3Re0C1 0 0 0

Ph3p Ph P. —C1 __)31 3 3 Cl h3P C1 Cl

Cl Cl PP h3 (A) (B) (C)

Fipurc la. Froni and Valonti's Reaction Scheme. HRo04 A > (Ph P) RoX 3,, 2 3 D

K2Ro 16 __E_ UNKNOWN------(Ph P) RoX ' (Rod) 3 2 2 Figuro lb. The Reformulatod Reaction Schomo. (Ph3P)2Ro0X3 (isomer 2) A L (I) HRe04 A (Ph3P) 2Ro0X3 ...... 4...(Ph3PH)(Ph3PRo0C14) C H rG (III)

(ph3p)2R00x2.0Et K F (II) (Ph P) RGI HYDROLYSIS 3A 2 2 PRODUCTS K2RoI6 - E (Ph3P)2RoI ) A. Ethanol, triphonylphosphino, hydrohalic acid (X=C1) B.Ethanol, triphonylphosphinc, hydrohalic acid (X=Br, I) C.Ethanol, triphenylphosphino, hydrazine hydrochlorido (X=C1) D. Halogen, bonzone solution. (X=Cl,Br,I) E. Acotonc, triphonylphosphine (X=I) F. Air, benzene, ethanol (X=I) G.Dichloronethano solution, hydrohalic acid (X=C1,Br,I) H. Ethanol (X=C1,Br,I) J. Benzene solution, hydrogon chloride. K. Dichloromothane solution, mater (X=C1,Br,I) L. Boiling acetono. 22. contaminated with the ethoxo-derivative (II), as shown in Figure 3b. The ethoxo-derivative was obtained for the bromide and iodide. This was because of the greater ease of ethanolysis of the bromide and iodide. The

chloro - complex (I) had to be 1-c:fluxed in ethanol (re-

action H) for nearly two hours to cenvert it completely to the ethoxide, whereas the iodu - complex (I) was con- verted to the ethoxo - complex (II) by just mashing with hot ethanol. The presence of hydrazine in the reaction of perrhonic acid with hydrochloric acid and ethanolic triphcnylphosphine gave complete conversion to the ethoxo

- derivative (reaction C) in less than 30 sec. (contrary to the statement by Chatt et al. (53)), but the compound subsequently decomposed, first to orange crystals, which mere not identified (this compound did not have the properties of (Ph P) ReNC1 reported by Chatt (27)), and 3 2 2 subsequently to a brown sludge.

The reactions of the ethoxo - complexes (II) in benzene with halogens to give the oxotrihalides (I), analogous to reaction D, were not successful, tars being obtained instead of crystals. Crystals could be obtained by treating the tars mith solvents containing potential hydroxyl groups such as ethanol and acetone. In this case the products always contained some triphenylphosphine oxide. In the reformulated reactions no' oxidation was 23. necessary to convert (II) to (I). Hydrohalic acid did not appear to give any product by direct reaction with (II), but if a dichloromethano solution of (II) was shaken with hydrohalic acid there was a rapid and Com- plete conversion to (I). Possibly under those conditions there was SOUG conversion of (I) to the salt (III), as in the chloride and bromide cases the dichloromethanc solutions assum-d the "barium green" colour of the salt rather than that of the yellow compound which was separated. Also unless (II), prepared by this method, was recrystallised from benzene, (in which the salts arc not soluble) the halogen analyses were high. (see Table 2.)

Table 2

Halogen analyses of products of reaction G

Compound Before recryst. After recryst. Calculated % halogen % halogen % halogen (Ph3P) Ro0I 37.2 34.8 34.4 2 3 (Ph2P) Re0Br 27.6 25.0 24.8 3 (Ph3- P)2R00 12.9 12.6 12.8 The chloro --salt, triphenylphosphonium pxotetrachloro- (triphenyiphosphine)rhenate(V), was subsequently isolated by treating a benzene, solution of theoxotrichlo- ride (I) with dry hydrogen chloride when the salt was precipitated.

An attempt was made to remove GXCGSS hydro- hallo acid from the dichloromethane solutions of the 24. oxotrihalo complexes by shaking with motor. The solutions underwent roaction, houevor, the gre n chlorido and bromide solutions turning brown-red and the red iodide solution going purple. .grown solids were procipi- tated from the tmu former solutions with petroleum other, and purple crystals were obtained from the iodide solution on evaporation. Apparently hydrolysis had taken place although it mas not possible to isolate pure products. Tho usu of alkali solutions instead of water in the roaction caused further decomposition of the product. From the analytical results the chlorido and bromide formed products of the typo(Ph3P)2Re(OH)0X2 whereas the iodide product was apparently (Ph3P)2Ro(OH)20I or (Ph3P)211e02I. The reaction botwoen triphonylphosphino and dipotassium hexaiodurhenate(IV) in acetone always gave somo totraiodobis(triphonylphosphino)rhonium(IV), a compound previously described by Colton (18). On some oc- casions, however, red crystals were obtainod, apparently the same as the material prepared by Froni and Valenti (55) but not examined by then. The crystals, which wore stable in vacuo, decomposod slowly in dry air to give a brown product. From analysos and infra-rod spectra it was concluded that the rod compound was diiodobis(triphonylphosphino)rhenium(II). At present this appears to 25. be the only non-chelating phosphine complex. of rhenium(II)

(sec: (53) for compounds of Re(II) with chelating phos- phines and (16) for cnelating arsines), as the two previous claims to have prepared this and similar compounds (53,55) have been shown to be incorrect (21,27). The. compound is interesting as, unlike the previous Re(II) compounds, it must have been four coordinate since it was monomeric. Unfortunately no magnetic measurements are available on this compound as it ‘Jas not examined in the initial preparations. Two recent attempts to prepare more of this material using potassium hexaiodo- rhanate(IV) prepared from new rhenium metal have boon unsuccessful. Attempts were made to prepare trichlorobis- (triphcnylphosphine)rhenium(III) by reaction of hexa- chlorodirhenium(III) with triphenylphosphine under various con-

ddtitns but only_trichlopotriphzay4labsOinerhenium(III) was obtained. Ebullioscopic molecular weight determinations in benzene solution showed that alt samples of the product were dimeric, in contrast to previous reports (18) that it was monomeric. This dincric species is presumably joined by two chlorine bridges and would thus be five coordinate. The compound could thereforc be diamagnetic, if the rhenium had trigonal bipyramidal coordination. In acetone the compound was monomeric. 26, Probably reaction took place with acetone forming a compound of the type P4.RoC13(acetune)9 which mould also be a five coordinate species of Re(III) anu thus diamagnetic, Although it bus nut possible to isolate this adduct9 this explanation of the diamagnetism seems more reasonable than the rather unusual d3s tetrahedral hy- bridisation which has been proposed for the monomeric form of trichloro(triphenylphosphine)rh nium(III) by Colton ut al. (18). Complexes similar to the above were made by addition of the ligand to hoxacblorodirhenium(III) for triphanylphosphino oxide triphenylarsine and triphenylarsine oxide. All wore too insoluble to determine the molecular weight. It should be noted that fur the former two compounds the analyses more slightly lomcr in carbon and hydrogen than required. Several attempts more made to remedy this by prolonging the reaction time but they more unsuccessful. Possibly the product contained a small amount of material of the type Ph PO.- 3 (ReC13)3.0PPh30 111 complexes of Re(V) prepared by us were diamagnetic. Octahedral complexes of a d2 ion should be paramagnetic with two unpaired spins. The x-ray structure of oxotrichlurobis(pho.nyldiethylpho§phina).t.t.) rhenium(V) has shown that thd M-0 bond is almost a triplc, 27. bond. This will be made up of a(r-bund between the pz orbital of the oxygen end one of the sp3d2 hybrid orbitals on the metal (see Figure 4.), and two A-bonds be- tmcon the oxygen p and p orbitals and the q d xz' yz orbitals on the metal. This will introduce a distortion into the t Levels, increasing the energy of the d 2 2g xz dyz orbitals and consequentLy lowering the energy of the dxy orbital, giving a diamagnetic species. Symons (105) has explained the diamagnetism observed in octahedral osmyl complexes in this may.

A summary of the infra-red data on those COM- pounds is given in Table 3. 28. Figure 4. The splitting of the t2g levels in ootahedra],yhenium(V) compounds oausqd by multiple bonding from ons_ligand. 1

Cl dxY Re--P -X-

1 Cl Plane xy Plane xz, yz.

2 dx2..y2, ,....,------(1, :tr.= dy2. '-, _-....-. dx2-Y2 ‹:orbitals dxyl______.=- xz,d dy . ....= xz, -d yz.-..-...... dxy. Ordinary Octahedral octahedral rhenium(V) ligand field 29. Table Infra-rod spoctra of phosphine complexes of Re(V) and related compounds.

Compound Ro=O Others

Re0C1 (PPh ) 3 3 2 isomer 1 969v s Re0C13(PPh3)2 isomer 2 982vs Re OBr 3(PPh3)2 981vs Re0I (PPh ) 981vs 3 3 2 Re0C13(AsPh3)2 967v s Re0C1 OEt(PPh 910v s -00H2 2 3)2 953s Ro0B 0Et(PPh3) 960s 911v s STOCH2 r2 2 Re0I OEt(PPh s - OCH2 2 3) 2 947s 903v S (HPPh ) (RooC1 PPh ) 979v s 2405m A) P,,T,E 3 4 3 (ReC1 .OPPh ) 1143v s P=0 3 3 n RoC1 (OPPh 1137v s 9 P=0 3 3 )2 (ReC1 ,OAsPh 850v sbr))As=0 3 3 )n 30. 3. ANALYSIS OF CYANIDE IN COMPLEX CYANILES. Some difficulty was experienced in gutting good carbon, nitrogen, and cyanide analyses in our in- vestigations of rhenium cyanides. Colton (42) also had difficulty in gutting good analytical results until using a method based on the murk of Adj.° and Browning (136), but mc could not get good results from Colton's appExatus.(4). As a result we investigated a number of methods of analysis and our results arc discussed here. At the time; some methods which gave good analytical results on compounds like K4Fe(CN)6 appeared to bo poor for the analysis of rhenium cyanides. This was because the standard rhenium compounds used were compounds prepared by Colton's methods and described by him as K3Ro(CN)8 and (Ph4As)2Re(CN)80H. While Colton did obtain the former compound his method of purification caused hydrolysis and the compound generally examined was almost pure h Re02(CN)4° Similarly, the latter 3 compound, which we did not manage to prepare, always appeared to be a mixture of hydrolysis products, ap- proaching in the limit, (Ph4As)2(Rc0.0H(CN)4). For this roason some of the methods were not investigated as thoroughly as could be, as they were discarded if the results did not fit Colton's formulations. Colton was not satisfiad that carbon and 31, nitrogen determinations by ignition methods on complex cyanides gave good results. This was checked by us and also by Macdonald (134). It was found that usually but not always the analysis for nitrogen on the standard substance was good, but analysis for carbon was nearly always inaccurate, usually in an unpredictable manner. For accurate carbon analyses, Macdonald found that much higher.t3mperaturcs,of-ijiition (1100°C. );lid to be used than normal (800°C.)9 with a vanadium pentoxide catalyst and cover. This method was not used because it was not completely reliable (see Table 4.). Analysis of nitrogen in the cyanides by the Kjeldahl method gave good results for potassium ferropyadidg but did not appear to be very good for rhenium cyanides. Colton determined cyanide by heating the compounds with concentrated sulphuric acid and measuring the volume of carbon monoxide evolved (31) using a reaction described by Adie and Browning (136). No practical details were given, either in the paper (31) or in Colton's thesis (133)4 but the apparatus was described in a letter (42) and is illustrated in Figure 5. A similar apparatus was constructed, but a number of practical difficulties were found. Adie and Browning examined the effect of sulphuric acid on ferro- and ferricyanides. They showed that the strength of sulphuric acid used in the attack 32. was critical; weak acid gave HON; H2SO4.2H20 gave CO; concentrated'acid gave CO, CO2, and S02. Assuming similar results for rhenium cyanides, concentrated acid would be too strong. Colton gave no evidence to show that concentrated sulphuric acid mould give the best results. 'A obtained reproducible results using acid concentrations between H2SO4.H20 and H2SO4.2H20. Concentrated sulphuric acid did not give reliable results. Colton's apparatus (Figure 5a.) had a total volume of about 350 ml. with a possible pressure variation of only a few inches of mercury. If a small quantity of material was used (20mg.) in the analysis it was difficult to control the temperature accurately enough to get a good estimate of the CO released, because of the large volume of gas in B. Also during the reaction the sulphuric acid fumes and the rise in temperature drove sufficient gas from A to give a total pressure increase of 20-30 cm. of mercury, which was sufficient to blow gas through the manometer. Be- cause of this we constructed the apparatus shown in Figure 5b. J was a 25 ml. flask with a neck about 5 cm. long, finishing in a B14 socket. The volume of this flask was accurately known. This could be connected to the measuring part of the apparatus, wtlich was an in- verted U-tube, one end finishing in a B14 cone, and the .other in a reservoir of about 15-25 ml. capacity (D). 33.

A. Reaction Vessel B. Gas reservoir C. Manometer PiWe 54 Colton' s ahharktug for cyanide ainalvass

A. Reaction flask B. U tube C. Calibrated side arm D. Reservoir E. Reservoir F.' Copper cooling guard

Fia47(1,%

The aoparatu used in this xo;1. for cy4xide_ vals.151p& 34.

A 1 mm, capillary side arm was joined in parallel to the

U-tube arm going to the reservoir. A long 1 mm. capillary

( -v-'90 cm.),was joined to the reservoir and pasL,ed close and parallel to the other capillary, finishing in a reservoir of about 25 ml. (E). The U-tube was calibrated from the cone to two marks on the opposite arm, C1 and C2.

Values of the volume between these two points were obtained by interpolation. When the flask was attached to the U-tube the system volume to any point between C1 and

C was known to 0.1 ml, 2 For a reaction, a knomn weight of sample (v50 mg.) was weighed into A. A known volume of cold, boiled sulphuric acid of the appropriate strength was added.

(The reaction did not proceed in the cold.) The measuring apparatus reservoir U was filled with sufficient mercury to give a level just below C1 when the tube was vertical.

The flask was sealed to the U-tube by melted black wax.

The whole apparatus, apart from the top of the long capillary, was immersed in a 20 gall. drum of meter at laboratory temperature (known to 0.1°C.) and allomed to come to equilibrium. The distance of the mercury below

(and thus the gas volume) and the difference between C1 the mercury levels in the two capillaries (which with the barometer reading gave the total pressure) were measured. The apparatus was than clamped in position, 35. the copper cooling guard filled with solid carbon dioxide and the reaction flask heated until all reaction had ceased (15-30 min.). After reaction the flask was allowed to cool in air and than equilibrated in the tank.

The volume, pressure and temperature were again measured and the total volume of gas released calculated. The method was based on the assumption that carbon monoxide was not soluble in sulphuric acid. Blank reactions, using no sample, produced no measurable change in volume.

The apparatus vas batter than Colton's because being smaller and more compact it was very easy to control the temperature of the whole system in the measuring stage. The smaller volume of the background gas gave much greater accuracy for a given meight of sample. The design also meant that even if the sulphuric acid was boiling vigorously no more than 25 ml. of gas at atmospheric pressure could be displaced to other parts of the vessel, and the volume of the rest of the vessel was effectively increased from 25 ml, when starting the reaction to 100 ml. mhen the amount of gas displaced mas a maximum (both volumes for gas at atmospheric pressure). Changes in the amount of gas in the apparatus because of gas released during the reaction are measured as changes in pressure rather than changes in volume, so that the range of volumes which has to be calibrated 36. is quite small (1.0 ml.), permitting high accuracy. At the time this method appeared to give poor results, but in the light of our present formulation of the compounds used es standards the method seems to be very good, as can be seen from Table 4. The method finally used ti c,s based on a method mentioned briefly in Inorganic Syntheses (135). .The sample was fused overnight ti ith potassium metal in a nickel bomb at 520°C. The potassium as destroyed mith methanol and the residue extracted with vater. The tvo solutions more filtered and combined, and the cyanide was estimated argentometrically. This appeared to be a very good method for the analysis of complex cyanides

(see Table 4) and vas used in all our cyanide work.

37. Table 4. Analysis of complex cyanides.

Method _ i Supposed compound Found ci, Calculated Ignition C N C N K3Co(CN)6 20.5 25.2 1 21.7 25.3 BaRe(CN) OH 11.7 12.2 i(A)17.5 20.4 8 X14.6 x 9.6 l(B)10.4 12.2 (Ph4As)2Ro(CN)80H 47.0 6.3 i(c)57.3 9.5 1())57.3 5.1 K ReN0H 0(CN) 2 2 4 12.5 18.0 1 12.0 17.5 H2SO4/C0 CN 1 CN K4Fo(CN)6,3H20 ' 38.3 37.0 39.0 1 (p1108)2Rc(cN)8oH 9.9 (0)17.7 (D) 9.5 K3Rc(CN) 23.2 (E)40.7 8 (F)23.7 Kjeldahl N N Klyo(CN)6.3H20 19.2 19.9 K3Re(CN)8 14.0 (E)21.9 (F)12.7 (Ph4As)2Re(CN)80H 8.0 (D) 5.1 7.3 Potassium, CN CN fusion . KqCo(CN)A 47.2 I 47.0 K4Mo(CN)8 45.1 45.2 K4w(u)8,2112o 35.9 35.6 K 3Ro(cN) 40.2 40.7 K2ReNH2'3(CN)L. 26.2 26.0 (?ft4As)2R0o.oH(cN)4 9.9 I 9.5

Note each analysis was done on a different sample. • x This analysis was performed by A. M. G. Macdonald, University of Birmingham (134). (A) BaRc(CN)ROH (D) (Ph4As)0Re0.0H(CN)4 (B) BaRe0.0HT0N)4 (E) KQRe(0NTA (C) (rh4As)2Re(U)80H (F) Kpe°2(CN)4 38 4. CYANIDE COMrLEXES. Griffith (106) has reviewed the stability of metal-cyanide complexes, and shown that while CN- is isoolectronic with NO+ and CO, it has batter Or-bonding properties. CN- is also receptive to back-bonding from the dg-electrons into the vacant carbon orbitals, and this undoubtedly occurs in many or all of the transition metal complexes, especially those which involve the metal in a low oxidation state. Compared with CO, CN- seems less efficient at receiving back-bonded electrons, the observed result arising from two conflicting effects. The better O'-bonding will make the ligand more electropositive and thus more able to receive electrons. However the negative charge on the ligand makes it more electronegative and thus less able to receive back-bonded electrons. Apparently the second effect outweighs the 'first. Thus me might expect CN to be less efficient than CO at stabilising low valencies. This appears to be the case for rhenium; the lowest valency carbonyl that has boon prepared is NaRe(C0)5 (-I) while the lowest valency cyanide complex that has been isolated is ye(CN)6 (I). The cyanide group is not expected to stabilise vary high valencies since the ligands which usually do this are small and highly electronegative (02-2 02- OH- 2 9 1 390 F-). The only well-established unsubstituted cyanides in high oxidation states are the eight-coordinated dl 2 and d compounds of Ro(V), Mo(V), Mo(IV), WV), and W(IV) (106) which are readily hydrolysed to oxo- or hydroxo-cyanides, where the presence of the highly electronegative ion helps stabilise the high valency. This stabilisation is shown by osmium where the highest valency oxocyanide is (0s02(CN)1)2 (VI) whereas the highest valency unsubstituted cyanide complex is Os(CN) 3 (III). Cyanide complexes of rhenium have been claimed for all the valency states 0 through 7, and these are summarised in Table 5. This mide range of valencies is unusual, and in view of the proceeding remarks, doubtful. Griffith has already queried the existence of cyanide complexes of rhenium in the 7 (106) and 0 (107) states. No compound has been isolated for Re(0) but Bannerjea and Tripathi (108) have obtained polarographically a seven electron reduction of perrhenate in solutions of potassium cyanide stronger than 0.5 M. Poor curves were obtained at weaker strengths than this. This work is in contrast to the work of Colton et al. (38) who reduced rhenium compounds in 0.1 M KCN solutions. Poor curves were obtained for the reduction of perrhenata but it was considered that the curves 40. might correspond to a 2 and 4 electron reduction to Re(V) and Re(I), which mould agree with the reduction of Ro(CJ)83- in 0.1 M KCN, when a 4 electron reduction to Rc(I) mas observed. Although Griffith '(107) hes ques- tioned the accuracy of Benncrjoa and Tripathi's work, the results presented scum reasonable. In fact the reliability of the work of colton et al. might be ques- tioned as further work at Imperial College under Griffith (107) has shown that the curves obtained from the polarographic reduction of porrhenate in 0.1 M KCN solution are quite unreliable. Attempts to interpret the curves have given several different values for the electron reductions, the maximum being 3 and 5 electron reductions to Re(IV) and Re(-I). At present polerographic evidence for rhenium valencies existing in cyanide solution must be treated with some reserve. A cyanide of Re(I) has been prepared by Krauss and Lissner (111) and Kleinbcrg (15). The compound has boon described as K5Re(CN)6 , although the analysis of Kleinberg's compound fits the formula K Re(cN) .xH 0. 57 5.7 2 Compounds of Ra(II) have been described by Indian morkers (110) but have not been reported by other workers on rhenium cyanides. Cyanide complexes of Re(III) exist, although their exact formulation is still questionable. Ro(CN)6 3" 41. Table 5. Reported cyanide complexes of rhenium.

Formal valency Complex Colour of Reference of rhenium potassium saLt in solution

VII Re(CN)80H2 Purple 31 2- VI Re(ON) Purple 8 31 V Ro(CW)83- Brown; yellow 31 (dilute) Ro0 (CN) 3- Pink 83 2 4 Yellow-orange 83 Red 91 3 (Re0 (CN)) Purple 83 2 4- IV Re0 (UN) Black 15 2 4 Re0.0H(GN)1 3". Redd 109 III Re(CN) 3- Green 31 6 Re(OH) (CN) 3- Blue 15 3 3 Re(CN) NO3- Red 31 7 3- II (Ro(CN)5H20) 110 I Re(CN) 5 Olive-gra n 111 6 0 Unknown m Unknown 108

••••••=.1••••••10•011

m Prepared polarographically 42. has been reported by Colton, while Kleinberg prepared De(OH)3(CN)31- 3- under similar conditions. As the colours of these compounds are different both may be correct. A nitrosyl cyanide of Re(III)„ CRe(CN)7Npi 3- 7 has been described by Colton (31). However this formulation may be incorrect as the evidence advanced for it is poor. Reactions between compounds of Re(V) and nitric acid do not normally lead to a reduction to Re(III). In addition Colton could not analyse the anion, basing his formulation on the Ag:Re ratio in the precipitated silver salt of approximately 3:1 However he admitted that these results were not good as the product was contaminated with silver cyanide and he could not decide between two possible formulae, De(CN)7N0.13- and [he(CN)5N0]3-. He chose the first formula on the basis of the release of 0.95 moles of HON per mole of K3Re(CN)8 reacting. But this result cannot be considered reliable as we have seen above enough free HCN was left in solution to give contaminating AgCN. In addition no attempt was made to take any account of hydrolysis which we have shown is very rapid under acid conditions. No simple cyano-complex of Re (IV) has been described although one has been postulated as an intermediate in Colton's (31) preparation of potassium octacyanida. An oxocyanide complex has been described by Kleinberg et al. 43.

(15) 9 K4Re02(CN)4, and a complex Kie0(OH)(CN)I:jhas been claimed by Turkiemicz (109). Morgan suggested (112) that this latter compound might be K3Re02(0N)4. However the original formulation may be correct. An analogous red compound of technetium has been prepared by Herr and Schmochau (113). In addition the potassium cyanide solution of rhenium dioxide used to prepare K3Re02(CN)4 was dark reds and had to be treated with hydrogen peroxide to lighten the solution to orange-red and probably oxidise it before pure potassium dioxototracyanorhenate(V) was obtained. Both cyano- and oxocyano-complexes of Re(V) have been described. As will be shown later, ions of 2- the type Ehe(CN)03-9 i?)02(CN)IJ- 3 9 and [RoO(OH)(CN)4] do exists although certain preparative methods do not give the compounds claimod9 and other compounds were wrongly formulated. These are discussed in more detail later. A cyano-complex of Re(VI) has been described by Colton although this was very unstable in solution. We have confirmed the existence of this ion. The ion in solution was previously assumed to be oxidised to a 2-5 species ERG(CN) (OH)J a complex of Re(VII). However 8 me have shown this was incorrect. In this work cyanides and oxocyanidas of Re(V)9 44. Re(VI), and Re(VII) have been investigated. As noted previously, potassium octacyanorhenate(V) was reported to be stable to hydrolysis, but this is unusual in view of the ease of hydrolysis of the octacyanomolybdate(IV V) and octacyanotungstate(IV & V) ions and the existence of a dioxocyanorhenate(V) ion. Potassium octacyanorhenate(V) could be prepared by Colton's method, although samples always contained a small amount of impurity, probably potassium octacyanorhenate. However purific,:tion by repeated evaporation with water followed by extraction with methanol, as recommended by Colton, caused complete decomposition, the product being potassium dioxotetra- cyanornenate(V) plus small amounts of potassium perrhenate and rhenium dioxide. Colton assigned a peak in the infra-red spectrum of potassium octecyanorhonate at 780 cm.-1 to an

Re-C stretch or possibly a C7IN wagging mode. If the latter assignment were correct a similar absorption should be observed in the infra-red spectra of octacyanomolybdate(IV) and octacyanotungstato(IV). If the former were correct, the Id-C stretch in the tungsten and molybdenum cyanides should be observed at the same or even higher frequencies than 780 cm.-1 as the M-CN bond should be stronger in the molybdenum and tungsten 45. cyanides, since there mill be more back-bonding because of the tomer formal charge on the motal. No such bands more observed. Pure potassium dioxotetracyanorhonato -1 has a very strong infra-rod absorption at 780 cm. 2 mhich has boon assigned to the Rc=0 stretch (1132 114).

We therefore assign the peak at 780 mm.-1 in K3Re(CN)8 as due to small amounts of K Re0 (GN) present as an 3 2 4 impurity. It mas possible to reduce the peak by carefully drying the methanol used as a solvent. It vas never possible to remove it completeLy. This may be because, as has been claimed (115), it is not possible to prepare pure potassium h-xsiodorhenatc(IV), (the starting product), or because of decomposition of potassium hexaiodorhonato by reaction with methanol the rod solution at room temperature rapidly became bromn on hosting. The salts of ERe(CN)812- described by Colton (31) were shown to be correctly formulated. 14omover attempts to prepare the ions Che(CN)02- and [Ro(CN)84]2-, 2- analogous to Cp(CN)801.13 , by treating solutions of K Ro(CN) in deoxygenated hydrochloric acid with cyanogcn 3 8 more unsuccessful. The only compounds obtained moro 2- salts of the purple ion CRe(CN)40(0H1 . A reexami- nation of the salts of the supposed [Re(CN)842- ion :1 2- showed that these also morc salts of the [Re(CN)0(OH)j ion. The same ion had been prepared but incorrectly

46. formulated by Morgan and Davies (83)7 their compounds B2H[e02(CN)1:1] being B2[1,e0(OH)(CN)47 (B was a monovalent bc4se). If the compounds were as formulated by Morgan and Davies there mould be a very strong band in the infra-red spectrum at 780 cm.-17 characteristic of the 0=Re=0 system in the Die02(UN)03- ion. No such band was observed. A band was observed at about 970 cm.-19 hovever, inhere the Re=0 stretch mould be expected for a linear 0=Re-OH grouping. The reaction of potassium octacyanorhenate(V) in oxygenated acid solution was formulated by Colton

HCl ReVI(cN) H20 Relr(CN) 3- ›. 2 >ReVII(CN) OH2- 8 8 8 02 02 It may now be rewritten as

HCl HC1 2- Rev(CN) 3- hevI(u)82 Re110(OH)(CN)4 8 0 2 H2O An oxidation and reduction reaction occuring under the same conditions on a similar ion seemed unusual but the products have been positively identified. It is possible to explain this anomaly by considering the reactions shown belom: Re(CN) 3" > RG(cii)82- (a) 8, Re(UN)61 ,i ii60(OH)(CN)42- (b) 2- Re(CN)82- > Re02(cN)4 or Re0(OH)(CN)4- (c) 2- Re02(CN)4 > Ro0(OH)(CN)42- (d) 47.

The oxidation reaction is represented by (a) and takes 2- place because under the experimental conditions Re(CN)8 is more stable than Re(GN) 3- But both these ions are 8 easily hydrolysed. Reaction (b) 9 although slover than

(a) 9 takes place as can be shown by suppressing (a) by excluding any oxidising agents from solution. The

Re(CN) 2- ion is hydrolysed by a reaction of type (c), 8 The reduction reaction is represented by (d) and occurs because the Re(V) hydrolysed species is more stable than the Re(VI) hydrolysed species.

A key point in Colton's assignment of the

780 cm.-1 infra-red band in K3Re(CN)8 was by comparison with a sample of K3Re02(CN)4 prepared by Morgan and

Davies' method (83). This compound had strong infra-rod -1 absorptions at 780 9 975 and 1000 cm. the former assigned to the Re-C stretch and the two latter to Re-0 stretches. Hovever9 as wo have shown9 pure K3Re02(CN)4 has no bands at 975 or 1000 cm.-1

We have prepared K3Re02(CN)4 by Morgan and

Davies' method (83) and obtained a spectrum for the product similar to that obtained by Colton. However it proved possible to separate this product into two com- ponents9 by treating with water. The component which was difficultly soluble in water shoved two strong ab- cm. -1 sorptions in the infra-rod spectra at 974 and 997 48.

but no absorption at 780 cm.-1 Strong absorptions were

also observed at 3740 9 3625 and 1620 cm.-1, characteristic of coordinated mater. On the basis of the analyses me have assigned the formulation K2ReN(CN)4.H20 to the

compound. Nitrido-compounds of rhenium have been prepared previously by hydrazine reduction of perrhenates in the presence of other ligands (27). The presence of -1 the two strong bands at 974 and 997 cm. is explained as follows A similar compound of osmium K[OsNBr4H2O3H20 -1 has a strong ki;N stretch at 1125 cm. (compare other

M;;N stretches (27) ) and an Os - OH2 wag at 925 cm.-1 (compare other M - OH2 wags (116) ). It is assumed that the structure of the NN(CN)4112012- ion is similar to

that of [OsNBr4H2d]- (117) with a linear N;Re - OH2 group and the four cyanides in a plane perpendicular to

this grouping (the single strong CAN stretch with very weak shoulders fits this formulation). The CN ion is

a strong electron donor along the ON-metal 6-bond and the electron density cannot be removed from the metal

by back-bonding to the cyanide ions as the metal dxz and dyz orbitals are used in bonding to the nitrogen. The excess electron density on the metal will cause weakening of the MI;di bond and thus lowering of the 11:41\T stretching frequency. It is postulated that this frequency is

lowered into the region of the weak band caused by the 49. M - OH 5 2 mag and that these bands interact by Fermi resonance giving the tlilo strong bands at 997 and 974 -1 cm. This compound is the first nitrido-cyano complex of a transition metal. Detailed infra-red spectra of the cyano-complexes of rhenium are given in Table 6. and the reaction scheme is illustrated in Figure 6. 50. Table 6. Infra-rud spectra of cyan-complexes of rn,3nium.

Compound Main bends in cm. (in Nujol mulls) K3 Re ( CN) 8 2140s, 2100s, 2050s (O'N str) ; 780m (R(3=0 str, impurity) E-Co(NH3)6j2 Do (CN) —3150m (NH Eitr) ; 2090s (CN str) ; 3 ---1500m5 b (NH loc:nd) K [Ro 0 ( 6N),71 2110s (ON str) ; 780v s (R(3=0 str) 3 2 4--1

K DioN(H 0) ( CN) 3740s, 3625m (OH str) °s 2160s ( CN str) ; 2 2 4 1620s (HOH bond) ; 997s, 974s (Re7_-N str, Ha -OH wag) [dipyH2/ [Re0( OH) ( CN) 2090s (ON qtr); 950 (lic =0 str)

[PhLos] 2 rlic0( OH) (CN)0 2190 5 2150m (CN str) ; 956 (Re =O str)

K [OsN(H 0 )Bri3 H2O 3470m5 3370m (OH str); 1590 (HOH 2 bond) ; 1110s (Os=N str) ; 917m,b ( Os-OH2 wag) 51. Figure 6. Cyano-compl3xos of Rhenium.

KReI 1 agic.,-,.(CN)813 -- 2 a --->[Re(CN)812- 2 6

K ReC1 d 4 b 3 b 2 a9 b 2 6 6 2- (Ph3P) 213.(10C120Et--11102(CN)0 3=-2 RoO(OH)( N)0 5b9 c,./„ I KReO4 >gWN(H20)(uN)0- 5 b

Referencos: (a) (31) (b) This work (c) (83) (a) (91) Rcagentst 1. KCN in CH OH 2. 4 M HCl iz air 3. 4 m Hc1.(cN)2 H 0 2 5. N H OH KCN H02 6 KaN59 H202 9 52. DIOXO-COMPLEXES OF RHENIUM. Hydrazine exerted a large catalytic effect on the ethanolysis of oxotrichlorobis(triphenylphosphine)- rhenium(V). It seemed possible that pyridine might also catalyse the reaction but not cause the subsequent decomposition observed in the hydrazine reaction. However the reaction followed a different course and an orange product was obtained, which from its conductivity was shown to be a 1:1 salt of formula (Repy402)C1.2H20 or (Repy4(OH)4)C1. The material could not be dehydrated in vacuo at 105°C. and showed no Re-0 stretch in the accepted diagnostic region 850-1050 cm.-1 (102, 118). A compound (Repy402)C1 has been reported by Russian workers (28), but since that compound was formulated only on the basis of rhenival nitrogen and chlorine analyses it seemed possible that it might be identical with our compound and that both might be the eight coordinate lvdroxo-species. Griffith et al. (119) had already suggested that 0A002(CN)04 should be reformulated as No(OH)4(CN)4]4-. Nuclear magnetic resonance examination of an acetone solution of the salt which shoved it was diamagnetic, was inconclusive. A peak of about four protons intensity was found in the area where either H2O or -OH could occur. Analogous bromide, iodide, hexachloroplatinate(IV), and tetraphenylborate salts, and a similar hydrated 53. ethylonediamine chloride wore prepared., the latter by substituting ethylenadiamine for pyridine in the reaction. The bromide, hexachloroplatinate(IV), and ethylenediamine salt all had two molecules of water per cation grouping, but the iodide was a monohydrate and the tetraphenylborate was anhydrous. None of these salts contained infra-red absorption peaks in the region 900-10u0cm.-1 Thera was a possibility that, in the case of the tetraphenylborate, a polymeric grouping existed, in which 'water had been eliminated but in which no Ro=0 groupings had been formed, as is known for rhenium com- 2- H20 4- pounds, e.g. 2(ReC150H) >(C15Re-0-Re015) (76) The molecular weight, 450, was shown to be in agreement with a 1:1 monomeric salt, 425. A dimoric 1:2 salt would have required a molecular weight of 570, and even higher values would occur with greater polymerisation. A more detailed examination of the infra-rod spectra of all these salts showed a strong peak at 820 cm.-1 which was not present in other compounds containing coordinated pyridine (120). This pock was assigned to the Re=0 stretch. The following argument is given in support of this assignment. The possibility of lowering the Ro=0 stretching frequency because of interaction with the water can be discarded because Johnson (103) prepared the anhydrous iodide by another method and tha-Re=0 stretching 54. frequency was still at 824 cm.-1 It is postulated that the very low stretching frequency is a direct consequence of the 0=110=0 system which is arranged as shown in Figure 7. In the similar octahedral rhenium system shown in Figure 4, with just a single oxygen atom, practically a triple bond existed between the metal and the oxygen. This was composed of a (r-bond and two j1-bonds using the d and d orbitals xz yz of the metal. In the system illustrated in Figure 7 both oxygen atoms will be competing for the metal d and dye xz orbitals in order to form multiple bonds. We suggest that one oxygen will form all-tIond between its px orbital and the metal d orbital and the other a (-bond between xz its py orbital and the metal d orbital. Instead of yz having almost a triple bond with a stretching frequency of about 950 cm.-1 we have in these complexes at the most a double bond with a much lower stretching frequency.

Another effect -which will also lower the stretching frequency depends on the other ligands. Like the nitridocyanide of rhenium, discussed previously, the orbitals normally used for buck-bonding to the ligands are now used in bonding to the oxygen. There is therefore no method of removing charge from the central metal atom other than weakening the metal-ligandcr-bonds and the metal-oxygen bonds. For a strong (r-bond electron do- 54a Figure 7, The ttauthse of 4ioxp-com4exest

.."

Plane xz Plane yz 55. nating ligand such as cyanide we mould therefore expect considerable weakening of the Re=0 bond and this was observed; the Re=0 stretching frequency dropped from about -1 820 cm. in the amine complexes to 780 cm.-1 in the dioxocyanorhenate(V) ion. There is considerable evidence in support of the structure proposed for those ions. Only one band which can be assigned to the Re=0 stretch is seen in the infra-red spectra as mould be expected. If the oxygen atoms were in the cis position there should be two infra- red active Re=0 stretches. Griffith has shown (121,122)

that octahedral osmyl complexes of the type (0s02L4)n -1 have Os=0 stretching frequencies between 800 and 850 cm.5 and in this case the structures of two of these compounds

K2E0 s02010 and K2[0s02(OH) have been determined by x-ray methods and shown to be of this type (1235 124). Furthermore, examination of the infra-red spectrum of -1 Desen 0 1 + in the region 850-900 cm. suggests that 2 2J the ethylenodiamine groups are trans rather than cis based on the criteria of Baldwin (125) meaning that the ion must be of the structure proposed. (see Table 7a.) If this explanation is accepted it is possible to make certain predictions which may be verified experimentally. In the case of phosphine complexes it was not possible to protonate the oxygen atom presumably 56. because all the electrons were delocalised in the mul-

tiple bond. In the dioxo-complexes each oxygen will

have two localised lone pairs of electrons and the oxygen should be easily protonated. Once one oxygen

atom is protonated the system reverts to that observed in the phosphine complexes of Re (U) the Re=0 stretching frequency should increase to about 950 cm.-1 and the second oxygen should be more difficult to protonate.

This was observed experimentally. The infra-red fre-

quencies of the dioxo-species prepared by us are given in Table 7, together with data for a number of other dioxo-compounds. It is evident that the infra-red diagnostic region for M=0 stretching frequencies must now be

extended downwards to at least 780 cm.-1 One assignment in Table 7 which is of interest is the Mo=O stretching frequency of dioxobis(2:4-propanedionato)molybdenum(VI). This differs from the previously published value of 935 cm.-1 (126). Assuming this compound had the same structure as other dioxo-

species, the 2:4-propanedione groups mould lie in the equatorial plane, so the infra-red spectrum was compared to that of bis(2:4-propanedionato)copper(II) which is planar. The spectra more practically identical except for a very strong peak at 906 cm.-1 in the molybdenum compound. Nakamoto et al. have examined the infra-rod 57. spectra of many 2:4-propanedione complexes of several different structural types (1279 1289 129). In all these compounds a band was observed at approximately 930 cm.-19 the upper and lower limits of this band in -1 all compounds being 944 and 921 cm. No other bands were observed below this in the spectrum until much -1 lower frequencies (about 800 cm. ). The spectrum of Mo02(acac)2 shows two very strong sharp bands in this region at 906 and 935 cm.-1 From the above observations it seems certain that the band at 935 cm.-1 should be assigned to a 2:4-propanedionc mode and the 906 cm. -1 band to the Mo.0 stretching mode. Finally it should be noted that the compound (Repy402)01.2H20 reacts in a different manner with concentrated hydriodic acid and hydrochloric acid. The compound (Rcpy40H.I)(I3)3 was formed unlike the product (Repy402)(Re0C1)5 reported by Russian workers (28). 58. Table 7. Infra-rod stretching frequencies for

octahedral dioxo-comhounds and related compounds.

Compound "N=0 Reference

(Ru.0402)C1.2H20 814vs + (Re.py402)Br.21120 819vs + (Re.py402)I.1120 824vs +

(Ro.py402)2PtC16.4h20 816vs + (Re.py402)BPh4 812vs +

(Re.on202)C1.2H20 814vs + (Re.en202)I 819vs + 906vs (A) + Mo02'(,,, cac) 2 K3Re02(CN)4 780vs2 br +

Cs2(Ru02C14) 8142 824 130 K2(0s02(OH)4) 790vs 121

K2(0s04(OH)2) 815 . 122 837 122 K2(0s02Cl4) Cs2(0s02(CN)4) 830vs 121

K (Os0 (C 0 ) ) 824 122 2 2 2 4 2 (NH ) )C1 808 122 (Os02 3 4 2 K2(0s02(OH)2(NO2)2) 883s (B) 121 K (Os° (OCH )1.) 820br 122 2 2 3 Lt. K (0s0 (NO )(140,)) 871vs (B) 121 2 2 3 3 ) + This mark. (A) This value differs from the published one (126). See text. (B) These cowounds contain other strong bands in the 800-900 cm.-1. region. It is possible that these bands more incorrectly assigned (107). 59. Table 7a. Infra-rod sp6ctra of 6thylenedis,mine comlcxes betue n 800-990 cm.-1

Compound )Re, =0 8.--OH Others

[RC G n2023 Gi 2H20 814v s 879v14 89414 [Re . n20 23 I 819vs 874m 882m De.on20.010(0104)2 981m 92914 873v' 88414 N.en2(OH)21(C104)2C1 927m 874v14 88714 [Re.en2(Ol- ) 2.2 [tC16.13 880m 890m "en.R60 " 902vsbr 3 60. 6. 2:4-PRO1ANEDIONE COMPLEXES Only one 2:4-propanedione complex of rhenium has been reported previously; this was tris(2:4-propanedionato)rhenium(III) (18). It was hoped to prepare

oxochlorobis(2:4-propanedionato)rhenium(V) by the re-

action of 2:4-propanedione and oxodichloroethoxobis- (triphenylphosphine)rhenium(V) in benzene for some infra-red spectral studies, but this was not the product obtained. The reaction gives at least three products depending on length of reaction time. A possible reaction scheme is illustrated below: a (Pi-h3)2Re0C120EL >(Pi,h3.)4te0C12(acac) (A) b d,„ -(- Ph ) Rea (acac) (B)----Rb(acac) (C) 3 2 2 3 The first reaction, a, is quite rapid as is the decomposition reaction, c, and the reaction has to be stopped when it is estimated that the amount of the required product (A) is at a maximum (a few minutes). Reaction b is also rapid but the decomposition reaction, d, is much sLower so that it is relatively easy to get a sample of (B) free from (A) (a few hours) although the reverse is not so. The decomposition reactions, c and d, may give rise to products other than (C) but these have not been identified. There is no evidence of (A) decomposing by the alternative reaction o.

All compounds were monomeric and thus octa- 61. hedrally coordinated. The Re(V) complexes were dia-

magnetic and we suggest that this was because of dis-

tortion of the t levels by the multiple-bonded oxygen 2g as outlined previously. The M-0 bonding in these com-

pounds must be almost as strong as in the starting pro-

ducts as the infra-red M=0 stretching frequencies are in the same region; ))Re=0 in cm. (PPh )Re0C1 (acac) 979 3 2 (PPh )Re0Br (acac) 976 3 2 (PPh )Re0I (acac) 3 2 975 (PEt Ph)Re0C1 (acac) 976 2 2 The orange-yellow products were shown from

the analytical results to be of the type (PPh3)3ReX2(acac) and infra-red measurements showed that no M=0 was present. But the nuclear magnetic resonance spectrum of these compounds shoved they all had a single very sharp high-

field line. This suggested the compounds might be dia-

magnetic hydrides; the analysis was not sensitive enough

to show the presence of extra hydrogen atoms. The spec-

trum of the chloro-complex was examined in detail. The high field line was +13.5 ppm. relative

to dichloromethana, but was not split as would be expected for a compound containing phosphine ligands joined directly to the rhenium atom. (Unpublished work by us has shown that the'high-field line of the hydrides 62. produced from the sodium borohydride reaction of oxodi- halogenoethoxobis(triphenyLphosphine)rb.;nium(V) in T.H.F. was split into a doublet caused by the 4 spin on the phosphorus nucleus.) An attempt to measure the intensity of this line relative to the protons of the phenyl group was unsuccessful as it was not possible to find the phenyl protons. (expected intensity ratios Ph:Hs 30:1 or 15:1.) The material was reexamined in chloroform solution in case the phenyl protons were under the solvent line; but apart from the shifted solvent line the spectra were identical. It was realised that despite the sharpness of the lines the compound was paramagnetic; very high field lines have been observed previously for paramagnetic compounds (139). The paramagnetism was confirmed by an n.m.r. measurement by Evans' method (140).

The formulation (PPh ) ReX (acac)s an octahedral complexs 3 2 2 was thus shown to be correct.

The magnetic moment found was itrf = 1.6 B.M. (corrected for Ligands at 296°K.). Octahedral d4 complexes should be paramagnetic with two unpaired electrons and thus tueff = 2.83 B.M. In previous studies of the 7 + magnetic moments of d4 rhenium compounds [Re(diarsine)2X2) (16) and Re(acac)3 (18) values of A-eft = 1.8-2.2 B.M. have been 'observed and these low values have been explained by spin-orbit coupling in terms of the theory of 63.

Kotani (141) . The observed moment was lower than any of these values but the moment for two Re(III) complexes

which should have a very similar structure to our compound, [(110)31)113ReI3,hadieGeff = 1.65 B.M. at room temperature (63). Other moments as low as = 0.5 B.M. / 'eff 3+' have been observed for the complexes Elle(NH3)0 at 300°K. (80). The magnetic moment of the compound was measured in the solid state over a range of temperatures by the Gouy method. The results are presented in Table

8 and Figure 8. The room temperature moment was lower than that in solution. This might be because of solid interactions but the accuracy of the magnetic moments is not sufficiently great to say whether this effect was real.

The solid state magnetic moment decreased with decreasing temperature, the magnetic moment varying line- arly with T2. This is expected for a d configuration with a large value of the spin-orbit coupling constant

35d. The value of this constant for this compound was calculated from the formula

toff = 6 52(kTr/ 5d for the solution magnetic moment. The value found,

6600, is very similar to that observed for the isoeloc- 4+ tronic Os 2 6400 (8o).

64.-

Temperature Ti corr x 106 L eff ToK /* 293.0 17.10 797 1.37 248.3 15.72 797 1.27 233.0 15.24 797 1.22 223.0 14.9 797 1.20 197.3 14.03 728 1.07 161.2 12.7 728 097 142.7 11.95 694 0..89 125.0 11.2 694 0.84 87.0 9.32 555 0.63

Table .

,Tjailzuziatasaa_af the magnetic moment of dichloro(2:4...proDanadionato)bisarikhenvl- phosohine)rheraum(III) with temnegature.

Figure, 8. T°K. 65. 2. OXIDES OF RHENIUM At various times oxides of rhenium have been claimed in all the valency states 1 through 8. These are summarised in Table 9. The three lamest oxides, prepared by solution methods (1429 25, 143, 144) are very poorly defined, and might be mixtures of other oxides and rhenium metal. Rhenium dioxide, first prepared by the Nod- decks (24) is a well established, meekly paramagnetic black solid with a monoclinic crystal structure of the Mo02 type (1-,7, 146), although a high temperature form with an orthorhombic structure is known (149). Rhenium pentoxide was claimed by Briscoe at al. (146)9 but it is now generally accepted (29 32) that this compound was actually Re0 prepared by Biltz and Lehrer (22). 3 Rhenium trioxide is very unreactive and has a cubic structure (150). The red and blue forms are identical analytically and by X-ray examination (137). Rhenium heptoxide is the highest oxide of rhenium and was first prepared by the Noddacks (24). It is a yellow-white crystalline hexagonal solid and is best prepared by burning rhenium in oxygen in a closed system (15r). Rhenium tetroxide was also claimed by the Noddacks (24) but has boon shown to be either hydrated rhenium heptoxide or perrhenic acid (152). 66.

Table 9e Supposed oxides of rhenium.

Oxide Preparation Colour Characterisation and References. Re 0 HRoOh + Zn/HC1 Black Poor (142) 2 (nit7ogen) Re0 HRe0), + Cd/HC1 Black Poor (142) (nitFogen) Re 0 ReCl, + OH- Black ' Poor (259 1439 144) 2 3 (nit?ogen) Re02 Re + Reo0,7 Black Certain (24) HRe04 +'Zh/HC1 (very dark (hydrated) brown) HRe04 + 142114 (hydratod7 0, Re + Ro 0 Purple, Ro27 2 7 green streak Doubtful (16) Re0 Repo? + Re Rod, Certain (22) 3 ReU0'+ Re207 Purple-rod Re2it7 +COJ ' Blue Re207 Re + 02 Palo yellow Certain (24) Re208 Re + 0 White _ 2 Non-existent (24) 67. Dry, but not anhydrous, rhenium dioxide was needed for some of our experiments. The normal method of preparation is to dry the hydrate in vacuo o at 400 C. In our experiments the hydrate, prepared by the hydrolysis of potassium hexachlororhenate(I\i), was heated in air at 185°C. for 48 hrs. Instead of the expected black dioxide, a bright purple-red substance was obtained. This material as very similar in appearance to a compound obtained by boiling perrhenic acid with hexachlorobutadiene for three days. The compound was dichroic, being green by transmitted light, and practically diamagnetic; it was very stable in air at 185°C., shop ing no significant change in composition over a meek. The infra-red spectrum was identical with that of rhenium dioxide hydrate. The composition was shown to be Re02.45. Briscoe (146) assigned the formula

Re205 to a compound of very similar appearance and pro- parties, although it mas prepared by the reaction of rhenium and rhenium heptoxide: Briscoe's compound was later reformulted as Re03 (22). Our compound ues examined by x-ray crystallo- graphic techniques. The material mas composed of two phases; one was Re03 and the other me have not identified, but it was not either of the forms of Re02. The data by which we identified the Re0 phase are presented in 3 68. Table 10. For the sake of completeness the full d - spacings are presented in Table 11. Apparently no one has attempted this experiment as there is no record of this in the literature. Anhydrous rhenium dioxide is reported to be oxidised in air directly to Re20r,7 above 150°C., and certainly it did not give the above reaction, However the maroon material was not oxidised because there was no change in -weight or composition, so no Re20 sublimed off. 7 Briscoe reported that red crystals of "Re 0 grew on 2 5 the faces of wet rhenium dioxide crystals when heated in air. We conclude that a stable phase Re205 first reported by Briscoe does exist. However this is a mixture of Re0 and another phase which is at present un- 3 identified. On one occasion under very similar experimental conditions (195°C/24 hrs. in air) a bright green, paramagnetic oxide was obtained ( = 2.5±0.5 B.M.). t eff The rhenium content corresponded to Re02.67. A similar compound was claimed by Noddack but was later shown to be incorrect (137). The infra-red spectrum was identical to that of the maroon compound. This compound was also examined by x-ray techniques. The d - spacings were not those of Re03 or either of the types of Re02. The data are presented in Table 12. 0/9 . Thy: results shoits that the system rhenium - oxygen is not yet fully characterised betvcen the limits Re° and Re0 this is being investigated fur- 2 3 ther. 70. Table 10. Powder data for Re0

g . 2n Index Intensity d sin °lobs.sin Q calc(A) a(B)

100 56 3.714 .0580 .0571 3.7166 110 53 2.620 .1160 .1142 3.7164 111 16 2.1557 .1725 .1713 3.7317 200 36 1.8651 .2318 .2283 210 66 1.6701 .2873 .2855 i:7318.37 211 43 1.5270 .3438 .3426 3.7317 220 28 1.3231 .4574 .4568 300 56 1.2470 .5145 .5139 i:74t 310 34 1.1826 .5718 .5710 311 27 1.1287 .6282 .6280 i:( a7 222 15 1.0802 .6849 .6851 3.7468 320 42 (0) 1.0387 .7415 .7412 3.7452 (D) 1.0386 .7455 .7146 321 70 fm 1.0015 .7984 .7982 i:M ((p) 1.0013 .8019 1 3.7453 400 20 5((,) 0.9370 .9117 .9112 3.7471 14 (D) 0.9366 .9160 .9161 3.7462 410 1 58 1(0) 0.9090 .9685 .9692 3.7474 32,:.J 100 (1,) 0.9090 .9730 .9733 3.7472 a = 3.746 .003 2 at the 95% confidence level. (A)calculated from finpl value of a. (B)calculated from sin4obs. (C)calculated for Ko<1 radiation 1.7889 (D)calculated for I 2 radiation 1.7927 Cobalt radiation was used with wavelength Kc( •= 1.7902 2 except as noted. corr.

71. Table 11. Powder data for the maroon oxide

Line Intensity sin2 e 1 16. .0580 2 20 .0705 3 n42.820 .1009 53 6 0 .1160 2 2. 5 .1297 0 16 2.1557 .11225 7 5 2.1090 .1800 8 25 1.8651 9 9 1.7182 .2709 10 1.6890 .2808 11 1.6701 12 ITS 1.5270 13 <2 1.4705 .3705 14 < 1.3839 .4185 15 102 1.3660 .4294 16 4 1.-1211 17 1.3079 .4686 18 13 1.2470 .514 19 2 1.2085 20 32-± 1.1826 21 22 22 2 1.0950 .6675 23 .6848 24. ...1 A B 1:842 4 25 1.01_ 26 2..Q A B 1.0015 27 1C 1.001.1 .801 28 2.5 0.9918 .8140 29 2.5 0.9845 30 5 0.9622 .8644 31 22 A TB 2_,.32.2.S2 .11 32 14 tc 0.9'1/26 .91 0 32 100 A 03 0.9090 .9685 34 --2 / C 0.9090 .97N Underlined data characteristic of Re03. A; doublet Cobalt Kc

Table 12. Ponder data for the green oxide. 72.

Line Intensity d sin28 1 50 3.184 .0791 2 120 2 .933 .0934 2.791 .1028 4 40 2.5264 .1255 5 .33857 8 2. .1408 6 46 2.2547 .1577 7 6 2.1160 .1789 8 4o 2.0018 .1991 9 91 1.9581 .2090 lo 31 1.8651 .2318 11 100 1.7522 .2609 12 39 1.6901 .2803 13 120 1.6321 .3008 14 54 1.6074 .3101 15 54 1.5883 .3176 16 22 1.4907 .3607 17 33 1.4661 .3737 18 14 1.4536 .3793 19 4o 1.4159 .3998 20 12 1.3696 .4273 21 4o 1.3386 .4474 22 8o 1.3240 .5714 23 1.2849 .4853 N 50 1.2716 .4962 25 21 1.2587 .05 57 26 21 1.2350 .524 6 27 40 1.2165 .5406 28 22 1.2020 .5540 29 25 1.1812 5730 30 20 1.1600 ..5948 31 33 1.1537 .6015 32 1.1099 .6494 33 V3 1.0790 .6872 34 5 1.0669 .7032 35 13 1.0448 .7283 36 15 1.0365 .7447 37 45 1.0250 .7619 38 1.0122 .7808 39 1 0.9931 .8114 4 0 37 0.98 40 .8262 41 34 09778. .8375 42 ca .50 A 0.9557 B .8758 43 {0.9542 C .8824 44 7 0.9320 .9200 45 36 A {0.9081 B .9705 46 7o 0.9081 0 .9740 A: doublet; Cobalt Ko(radiation used: a1-1.7889 2(B); o<2 -1.7927 A(C); oceanm 1.7902.E 73. 8. WAPERIMENTAL Carbon, hydrogen, nitrogen, oxygen, halogen, arsenic and phosphorus analyses and molecular weight determinations were performed by Imperial College Micro-

analytical Laboratory. Other analyses were performed gravimetrically by the methods used in Vogel's "quan- titative Analytical Chemistry. Potassium was determined by a semi-micro modification of the tetraphenyl borate

gravimetric procedure (153).

Infra-red spectra mere recorded using a Perkin- Elmer Model 21 double beam infra-red spectrometer, mitb sodium chloride or calcium fluoride optics. Routine

spectra were recorded on an Infra-cord machine with sodium chloride optics. Nuclear magnetic resonance

spectra were measured on a Varian Associates Model 4300B spectrometer at 56.45 Mc/s. Routine magnetic measurements on solids were made using the Gouy method (154)

and on solutions by the n,m.r. method of Evans.(140.).. The

variable temperature measurements were made by the Gouy

method, in duplicate in a perspex tube, checked over the whole temperature range to ensure no temperature

dependent paramagnetic effect. The magnets were calibrated with standard nickel chloride solutions (80).

X-ray spectra were performed on powder samples in

Lindemann tubes using cobalt Kc

CH2C12 solution by the n.m.r. method. It melted with decomposition at about 150°C. Oxodiiodoethoxobis(triphenylphosphine)rhenium(V) Perrhenic acid (1 g.), 45% hydriodic acid (2 ml.), triphcnylphosphine (5 g.) and ethanol (20 ml.) were boiled together for about five minutes. The green crystals of the compound were filtered off, recrystallised from a dichloromethano - ethanol mixture and dried in vacuo (250C/0.1 mm.). Yield 3.1 g. (76%). EFoundt C, 44.3; H9 3.4; 15 24.3; 0Et5 4.0%; M9 1034. C33H35I202P2Re requires C, 44.5; H, 3.4; 12 24.7; OEt, 4.4c/0; M, 104 The compound mas diamagnetic as the solid and in CH2C12 solution (n,m.r,) and molted with decomposition at about 155°C. Oxotrichlorobis(tripnenylDhosphino)rhenium(V) (isomer 1) A boiling solution of triphenylphosphine (5 g.) in ethanol (10 ml.) was added to a boiling solution of perrhenic acid (1 g.) and concentrated hydrochloric acid ( 1 ml.) in ethanol (10 ml.) and the mixture refluxed for three 77. to five minutes. The yellow-green crystals of the compound were separated and recrystallisod from benzene. Yield 2.6 g. (78%). `Found; C9 51.0; H9 3.8cio'd The compound prepared by this method was sometimes contaminated with small amounts of oxodichloroethoxobis(triphenylphosphino)rhenium(V). An alternative method was to shake a solution of oxodichloroethoxobis(triphenylphosphine)rhenium(V) (1 g.) in dichloromethane (100 ml.) with 6M hydrochloric acid (3 ml.) until the organic layer went bright green. The dichloromethane layer, which was carefully separated, started to deposit yellow crystals immediately. The layer was treated with a large excess of petroleum ether (400-60°) to ensure complete precipitation. The compound was filtered off, and dissolved in boiling benzene. The hot solution was filtered and treated with an excess of petroleum ether (40°-60°). The solid was filtered off and dried in vacuo (40°C/0.1 mm.). Yield 0.8 g. (79%). [Found o C9 50.5; H9 3.8; Cl, 12.6. C36H30C130P2Re requires C, 51.9; H9 3.5; Cl, 12.4;.1 The green solution Was probably caused by the presence of Ph3PH(Ph3P.Re0C14) which was prepared by another method and was identical in colour. The compound was diamagnetic in the solid phase; it was not sufficiently soluble to determine the magnetic properties in solution. It decomposed at about 200°C. 78. Oxotrichlorobis(tribhenvlbhosphine)rhenium(V) (isomer 2) Oxotrichlorobis(triphenylphosphine)rhenium(V) (isomer 1) was suspended in acetone (50 ml.) and boiled under ref lux in nitrogen overnight. The green crystals which had precipitated were filtered off, mashed thoroughly mith acetone and diethyl other, and dried in vacuo (25°C/0.1 mm.). Yield 0.9 g. (90%). D'ound: 0, 51.85 H, 3.9. 0 ,H30 Ul OP Re requires C, 51.9; H, 3.5%] The compound 30 3 2 was diamagnetic in the solid state and not very soluble in organic solvents. The infra-red spectrum showed an Be=0 stretch at 981 cm.-1 No peaks were observed in the -0H OH and -PH characteristic regions. 9 2 The same compound could be obtained by substituting oxodichloroathoxobis(triphonylphosphine)rhonium(V) in the above reaction, but in much lower yield (f-,50%). The supernatant solution which was red-brown after reaction yielded a brown tarry substance on evaporation. This product vas reprecipitated from dichloromethane solution by petroleum other, but could not be obtained pure. The infra-rod spectrum shoved no Re=0 band present but the compound contained Ph I-2 PhP0, OEt and OH groupings. Oxotribromobis(triphenylphosphino)rhenium(V) Oxodibromoothoxobis(triphonylphosphinc)rhenium(V) (2 g.) vas dissolved in dichloromethane (100 m1.) and the solution 79. shaken with concentrated hydrobromic acid (5 m1.). The green dichloromethano layer was separated and treated with excess petroleum other (40°-60°). The yellow compound was filtered off, recrystallised from boiling benzene and dried in vacuo (25°C/0.1 mm.). Yield 0.7 g. (67%). [Founds C, 44.9; H, 3.7; Br, 25.0. C3030Br30P2Ro requires C, 44.7; H, 3.2; Br, 24.8-] Oxotriiodobis(triphonylphosphinc)rhenium(V) This was prepared in a similar manner to the proceeding compound using 45/0 hydriodic acid instead of hydrobromic acid. Yield 0.9 g. (83h). [(Pound: C9 38.5; H9 3.1; 19 34.8%; ki9 1100. C3030130P2Re requires C, 39.1; H, 2.7; I, 34.4; M9 1107] Hydrolysis of oxotrichlorobis(trichenyl-Jhosphine)rhenium(y) Oxodichloroothoxobis(triphunylphosphine)rhenium(V) (1 g.) was dissolved in dichloromothane (100 ml.) and shaken for two minutes with 6M hydrochloric acid (10 ml.). The aqueous layer was separated. The dichloromethanc layer was shaken vigorously for three minutes each with three separate (20 ml.) portions of water, the aqueous layer being discarded each time. The dichloromethane layer became brown-maroon. It was poured into 400-60° petroleum ether (100 ml.) when a brown solid separated. This was filtered off and redissolved in the minimum amount of dichloromethane. 40°-60° petroleum ether (300 ml.) 80. was added slowly to the filtered solution with vigorous stirring and brown crystals precipitated. These were separated, washed thoroughly with diethyl other, and dried in vacuo (25°C/0.1 mm.). Yield 0.7 g. [Found: 0, 53.8; H, 5.0; Cl, 9.7% h., 789. C36H31C1202P2Re requires C, 53.1; H, 3.4; Cl, 8.7%; M, 814 The analysis corresponded to about 75,- conversion to the required product. Attempts to prepare a purer product by using hot mater, or alkaline solution were unsuccessful, the dichloromothane solution depositing a black flocculent precipitate. Hydrolysis of oxotribromobis(trinnenylonosphine)rhonium(V) Oxodibromouthoxobis(triphenylphosphine)rhenium(V) was treated in a similar manner to the chloro - compound above; a similar coloured solution was obtained, and rather darker brown precipitate. Yield 0.6 g. (-J60%).

EFoundz C, 44.7; H9 4.75 Br, 21.3%; M9 927. C36H31Br202P2Re requires C9 47.9; H9 3.5; Br, 17.75 119 904. The analysis corresponded to about 50% conversion. Hydrolysis of oxotriiodobis(tribhenylphosphinc)rhenium(V) Oxodiiodoethoxobis(triphenylphosphino)rhonium(V) was treated in a similar manner to the cnloro - compound above. A bright purple solution ias obtained with a small amount of black precipitate. This was filtered 81. off before pouring the dichloromethane solution into 500 ml. of petroleum ether (40°-60°). No precipitate was obtained. On standing, purple crystals separated. These mere filtered off, mashed with petroleum ether (400-60°) and dried in vacuo (25°C/0.1 mm.). Yield 0.3 g. (-./30A. C, 47.6; H9 3.5; /9 17.1%; M9 900. C3031103P2Re requires C, 48.7; H9 3.6; I, 14.3%; M9 888. C3030102P2Re requires 0, 49.7; H9 3.5; 19 14.6%; M9 8701 It was not possible to determine which of these two formulae was correct. Expressed as hydrolysis relative to (Ph P) Re0I the results correspond 3 2 3 to about 85% conversion. .Again further attempts at purification gave complete decomposition of the product. Oxotrichlorobis(tribhenylarsine)rhenium(V) Rhenium metal (1.0 g.) was dissolved carefully in 30:, hydrogen peroxide (50 ml.) and the solution evaporated to dryness. The resulting perrhenic acid was dissolved in concentrated hydrochloric acid (1.0 ml.) and added to a suspension of triphenylarsine (3.0 g.) in glacial acetic acid (50 ml.). The suspension mas stirred for an hour, then the solid filtered off, mashed with glacial acetic acid and diethyl ether, and dried in yacuo (25°C/ 0.1 mm.) to give the required product as green-yellow microcrystals. Yield 3.7 g. (75%). ['Found: C, 46.6; H9 3.3; is, 14.8; 0, 2.3; Cl, 11.2%. C6H30As2C130Re 82. requires C9 47.0; H, 3.3; As, 16.3; 05 1.7; Cl, 11.6 Triphenylphqsplionium oxotetrachloro(tri2ilenylphosphine)- rhenium(V) Oxotrichlorobis(triphenylphosphine)rhenium(V) (1 g.) was dissolved in hot benzene (100 ml.) and hydrogen chloride was passed into the solution. A green crystalline solid was precipitated. The compound was filtered off and mashed thoroughly with hot benzene and dried in vacuo (80°C/0.1 mm.). Yield 0.9 g. (89%). rFound C9 49.25 H9 3.19 C19 16.0. C18H31C140P2Re requires C9 49.7; H, 3.6; Cl, 16.3%.i The compound mes a green diamagnetic solid, giving a conducting solution in nitrobenzene 0_(1.44 x 10-3M) = 8.8 mho.cm A(0.36 x 10-314) = 9.7 mho.cm.2). This value is Lower than that expected for a uni-.uni.valent electrolyte in nitrobenzene (-J20- 30 mho.cm.2) and the compound was evidently appreciably associated. Similar low results have been observed previously for other phosphonium salts, for example; - (138). The presence of the EPHEt2Ph][JrC14(Et2Ph)2_ phosphonium group was also indicated by the P-H stretching -1 frequency in the infra-red spectrum at 2410 cm. Hexachlorobis(trlaLenylphosptine)dirhenium(III) This compound, which had been described previously as monomeric (18), was prepared by three different methods: (a) The reaction of triphenylphosphine and hexachloro- 83.

dirhenium(III) in boiling acetone solution. (b) The reaction of the product from (a) with fused triphenylphosphine. (c) The reaction of fused triphenylphosphine and hexa- . chlorodirhenium(III). On removal of the excess triphenylphosphine by solution in hot diethyl ether the products appeared to be the same as that already described by Colton (18) and Freni and Valenti (55). However the molecular weight determinations in benzene (obullioscopically) showed all samples to be dimeric. [(Pound: C9 39.7 (a), 39.5 (b), 39.6 (c); H9 3.1 (a)9 (b)9 and (c); C19 19.4% (a); 15 1120 (a)9 10709 (b), and 1070 (c). Calculated for C3030C16P2Re2 : C9 39.09 H9 2.7; Cl, 19.2; M5 1109:j When the molecular weight was measured in acetone (ebullioscopically) the compound slowly dissolved giving a bright red solution. The molecular weight was 520 indicating the compound was monomeric. Tetrachloro(triphopy1phosphine)rhenium(IV) Rhenium pontachloride (1 g.) was mixed with triphenylphosphine (3 g.) in dichloromethane (or acetone) (100 ml.). The green solid which separated mas filtered off9 mashed thoroughly with ethanol and ether, and dried in vacuo (40°C/0.1 mm.). Yield 0.6 g. (37%). [pound: C, 37.95 H9 2.2; Cl9 24.1; P9 5.3%. C181115C14PRe requires C, 84.

36.6; H, 2.2; Cl, 24.0; P, The compound was not soluble in the common organic solvents and was probably polymeric. No bands were observed in the infra-red spectrum in the characteristic 0-H, M=0, P=0, and stretching regions. The magnetic moment was-.,1.2 B.M. at

296°K. in the solid state. Diiodobis(tripqqnYlphosphine)rhenium(II) Freshly prepared potassium hexaiodorhenate(IV) (2 g.) was boiled with a solution of triphenylphosphine (5 g.) in dried acetone (25 ml.) in a nitrogen atmosphere.

The bright red crystals of the compound were collected, recrystallised from deoxygenated benzene in an inert atmosphere and dried in vacuo (25°C/0.1 mm.). Yield 0.8 g. (40%). [Foundz C, 44.3; H, 3.8; I, 25.8%; M,

981. C36H30I2P0e requires C, 44.8; H, 3.1; I, 26.3%; M9 964.1 The crystals were apparently stable in vacuo, but decomposed sloWly in air to a brown powder. In benzene, the compound decomposed slowly but this could be prevented by deoxygenating the solvent. It decomposed readily in oxygenated or halogenated solvents.

The infra-red spectra showed no bands in regions other than those assigned to triphenylphosphine modes.

Tri.chlorobis(triphenvlphouhine oxide)rhenium(III) Hexachlorobis(triphenylphosphine)dirhenium(III) (1 g.) and triphenylphosphine (0.5 g.) mere suspended in acetone 85. (100 ml.) and two drops of water added. Chlorine gas was bubbled through the solution until it became hot and a bright, clear, red solution was obtained. Passage of chlorine was continued for a further fifteen minutes. The solution mas reduced in volume at a vacuum pump (10 ml.) and then poured into diethyl ether (200 ml.) which was stirred vigorously. The solid was separated, redissolved in acetone (10 ml.) and reprecipitated with diethyl ether (200 ml.). Thu solid was separated and dried in vacua (25°C/0.1 mm.). Yield 1.1 g. (72%). Teund: C, 51.9; H, 4.1.; Cl, 13.1%; M9 810. C36H30C1302P2Re requires C, 50.9; H, 3.6; Cl, 12.5%; M9 849:3 'The compound was diamagnetic, readily soluble in acetone, ethanol, and chlorobenzene, sparingly soluble in dichloromethane and benzene and insoluble in diethyl other and petroleum ether.

) A solution of hexachlorodirhonium(III) (1 g.) in acetone (50 ml.) was added to a boiling solution of triphenylphosphine oxide (2 g.) in acetone (50 ml.). The solution was boiled gently for a few minutes and the red- purple crystals of the compound filtered off. The compound was mashed with a little acetone and diethyl ether and dried in vacuo (25°C/0.1 mm.). Yield 1.5 g. (90%). [Found: 0, 36.0; H, 2.5; Cl, 19.7%. 018H15C130PRe re- 86. quires C9 37.9; H, 2.6; C19 18.6g.1 The material was not appreciably soluble in the common organic solvents. The supernatant solution from the above reaction, on evaporation to a small volume and removal of trichloro- (triphenylphosphine oxide)rhenium(III) which separated, yielded a small quantity of trichlorobis(triphenylphosphine oxide)rhenium(III) when poured into excess ether. Pound: C5 49.6; H, Trichloro(triphenylarsine)rhenium( III) This was obtained in an exactly similar manner to the above compound, substituting triphenylarsine for triphenylphosphine oxide in the reaction. Yield 0.9 g. (44%).

[Found: C9 34.85 H9 2.2. C18H15AsC13Re requires C, 36.1; H, 2.54 Trichloro( triphenylarsine oxidelrhenium“II) This was prepared as the two previous compounds, only using triphenylarsine oxide as the ligand. Yield 1.2 g. AsC1 ORe re- (57%). [Found: C9 36.0; H9 2.4%. C18H15 3 quires C, 35.2; H, 2.5°4 Potasbium octacyanorhenate(V) Freshly prepared potassium hexaiodorhenate(IV) (75) (2 g.) was dissolved in methanol (distilled from sodium) and run into a boiling solution of potassium cyanide (1 g.) in methanol (100 ml.), and the mixture boiled under reflux for ten minutes. The brown solid which separated was 87. filtered from the hot solution, suspended in more dry methanol (100 ml.) and ref luxed for ten minutes. The compound was filtered off, mashed with hot methanol and dried in vacuo (25°C/0.1 mm.). Yield 0.7 g. (71%). [Found K, 22.9; CN, 40.2%. Calculated for K3Re(CN)8: K, 23.1; ON, 40.7 The product was diamagnetic. The hydrolysis of potassium octacyanorhenate(V) Potassium octacyanorhenate(V) (0.5 g.) was dissolved in water (5 ml.) and evaporated to dryness in a small diSh on the steam bath. The evaporation was repeated four more times, starting with 5 ml. of water each time. The residual solid, which was dirty white, was slurried with methanol (50 m1.), filtered off and dried in vacuo (25°C/0.1 mm.). [Found: CN, 22.0. Calculated for K3Re02(CN)4: CN, 23.n; for K3Re(CN)8: CN, 40.7%.] The infra-red spectra of the mixture showed, peaks characteristic of K3Re02(CN)4, KR004 and Re02. Potassium dioxotetracyanorhenate(V) Oxodichloroethoxobis(triphenylphosphine)rhenium(V) (2 g.) was suspended in methanol (50 ml.) containing potassium cyanide (1 g.). The mixture was boiled under reflux for four hours and the solution filtered while hot. The creamy-white compound was washed thoroughly with methanol and dried in vacuo (25°C/0.1 mm.). Yield 0.5 g. (48). [Found: K, 27.05 CN, 24.35 0, 6.5%. Calculated 88. for K3Re02(ON)4: K, 26.7; CN, 23.7; 0, 7.3%d When recrystallised from mater by allowing slow evaporation of the solution the compound separated as orange crystals.

The compound was diamagnetic. Hexamminecobalt(III) octacyanorhenate(VI)

Potassium octacyanorhenate(V) (0.5 g.) was dissolved in oxygenated water (5 ml.); and the solution acidified with hydrochloric acid. A saturated solution of hexamminecobalt(III) chloride (5 ml,) was added immediately. The black precipitate which separated as filtered off, mashed thoroughly with water and dried in vacuo (25°C/ 0.1 mm.). Yield 0.2 g. (10%). [Pound: Co, 7.8; ON,

42.7%. Calculated for Fpo(NH3)61 2r4le(CN)81 3: Co, 7.85

ON, 41.5%:] The compound was paramagnetic. kt = 1.9 at 298°K. corrected for ligands. The solid on standing in water slowly dissolved giving a purple solution. Tetraohenvlarsonium oxohydroxotetracyanorhenate(V)

Method 1: Potassium octacyanorhenate(V) (1 g.) was dissolved in water (10 ml.) and treated with concentrated hydrochloric acid (2 ml.). The solutiu.n was allowed to stand for 15 minutes and an excess of an aqueous solution of tetraphenylarsonium chLoride was added. The purple precipitate was filtered off. It vas dissolved in acetone (15 ml.) containing a few drops of mater, and then reprecipitated by pouring the solution slowly 89. into vigorously stirred mater (400 ml.), The blue- purple compound was filtered off and dried in vacuo (25°C/0.1 mm.). Yield 1.9 g. (95 ,). [Found: As, 14.1; CN, 9.99 09 3.1. C52H41As2N402Re requires As, 14.1; ON, 9.6; 0, 2.9%. The compound vas diamagnetic. Contrary to Colton's report (31) the compound vas not vary soluble in acetone. Homever it dissolved readily if a few drops of uator More added even though the compound was vir- tually insoluble in meter. Method 2: potassium dioxotetracyanorhenata(V) (0.5 g.) was dissolved in 4M hydrochloric acid (5 ml.). A 4M hydrochloric acid solution of totraphenylarsonium chloride was added and the compound filtered off. It vas purifiedfied as described above. Yield 1.1g. (95,0. Found: /puri10.0; 0, 3.2%j oxohydroxotetracyanorhenate(V) Potassium dioxototracyanorhenate(V) (0.5 g.) was dissolved in 4M hydrochloric acid (5 ml.) and a solution of y<'-bipyridyl (1 g.) in 4M hydrochloric acid (5 ml.) added. The purple compound vas filtered off, mashed with two portions of 4M hydrochloric acid (5 ml. each) and dried in vacuo (25°C/0.1 mm.). Yield 0.2 g. (45%).

[Found: CN, 2 .2; 0, 6.3%. °14H11N8 02Re requires ON, 21.7; 0, 6.7%.] Barium oxohydroxototracyanorhenate(y1 dihydrato Potassium octacyanorhenate(V) (1 g.) was dissolved in 90.

deoxygenated water (50 ml.) and concentrated hydrochloric acid (55m1.) added. Cyanogon was bubbled through the solution for two hours. A saturated solution of barium chloride (5 ml.) was added and the purple precipitate filtered off) mashed vith a little vater2 then ethanol and diethyl other. It mas dried in vacuo (250C/0.1 mm.), Yield 0.3- g. (3*). [Founds Bcrl, 27.0; H9 1.0; N, 10.6; 02 12.2%. C4H5BaNL0Re requires Bag 27.6; H9 1.0; N2 11.3; 09 12.9% The compound was diamagnetic. 'Potassium nitridoaquotetracyanorhenate Potassium porrhenate (1 g,) was suspended in an aqueous solution (30 ml.) of potassium cyanide (2 g.). Hydra- zine hydrate (5 ml.) was added and the mixture heated on a steam bath for a meek under nitrogen. The solution slowly changed colour through yellow and orange to an intense red. The liquor vas filtered and poured into excess methanol mhon a red oil precipitated. This was redissolved in the minimum of mater and again precipitated with excess methanol. The oil was finally dissolved in water (10 ml.) and methanol (5 ml,) added. The solution was allowed to evaporate in a desiccator containing anhydrous potasAum carbonate for a week. The 'rod crystals were filtered off and then slurried successively with three 2 ml. portions of water. The pink crystals remaining mere dried in vacuo (100°C/0.1 mm.), 91. Yield 0.4 g. (29'h). [Found: K9 20.1; C9 12.5; N9 18.0; 05 3.4; H, 0.9; ON, 26.2;.. O4H2K2N50Ro requires K5 19.5; C9 12.0; N5 17.5; 09 4.0; H, 0.4; CN, 26.0q The valency of the rhenium was 4.91 and the compound as diamagnetic. The water was very tightly bound, as no obser- vable exchange had taken place when 0.1 g. of the compound was shaken with heavy water for 14 hrs. at room temperature. The compound was not very soluble in mater, but dissolved readily in dilute hydrochloric acid. Potassium nitridototrabromoaquoosmateIVII monohydrate This vas prepared in the manner described previously

(137). rotassium nitridoosmate(VIII) (1 g.) was dissolved in conc. hydrobromic acid (5 ml.) in e flat dish and allowed to evaporate overnight. The pink crystals were filtered off and rubbed between filter paper to remove excess hydrobromic acid. The compound was dried in vacuo (25°0/0.1 mm.). L.Found: K9 6.51.. Calculated for H4Br4KN020s: K, 6,7c/;] Dioxotetrabyridinorhonium(V) chloride dihydrato Oxotrichlorobis(triphenylphosphine)rhenium(V) (1 g.) and pyridine (2 ml.) in ethanol (20 ml.) vere boiled under reflux for about 2 hrs. The orange solution was treated with an excess of diethyl other (200 ml.) and stirred vigorously. The yellow-orange precipitate of the compound was filtered off, recrystallised from methanol, and dried 92.

in vacuo (100°C/0.1 mm.) for 48 hrs. before analysis.

Yield 0.55 g. (75%). [Found G, 39.6; H9 3.9; N, 9.1; 0, 10.8; Cl, 5.9. 020H24C1N404Re requires 0, 39.6; H,

4.0; N, 9.25 0, 10.6 9 Cl, This compound was also obtained as one of the products formed by the addition of pyridine to an acetone solution of pentachlororhenium(V). The green

crystals mhich separated were filtezed off and the or-

ange supernate was evaporated under reduced pressure

(25°C/0.1 mm.). Orange crystals separated which were recrystallised from methanol. LFoundo 0, 39.7; H, 4.1; N, 9.6; 0, 10.2; Cl, 5.9%.1 The compound is soluble in water, pyridine

and ethanol, but is sparingly soluble in chloroform and acetone. It is insoluble in benzene, nitrobenzene and diethyl ether. It decomposed when boiled in mater, but was stable indefinitely in ethanol containing a trace of pyridine. The conductivity in water (.A.(1 x 10-3M) = 61.0 mho,cm.2) is that expected for a uni-univalent electrolyted. The compound was diamagnetic both as a

solid and in solution (n.m.r.). The green material, which was not identified, was insoluble in organic solvents and mas very sparingly

soluble in mater. The infra-red spectrum showed no

Re=0 stretch and there was no pyridinium present, but 93. coordinated muter was observed. The analysis of the compound fits the formulation Dy3.H20.ReC127G13.2H20.

[Found: C, 27.3; H, 205; N, 6.3; 0, 7.7; Cl, 28.910. C15H21C1 5N303Re requires C, 27.5; H, 3.2; N, 6.4; 05 7.3; Cl, 27.1%.] Dioxotetrauridinerhenium(V1_12romide dihydrate This compound was prepared as an orange salt in a similar manner to the chloride, starting from oxodibromoethoxobis(triphenylphosphine)rhenium(V) (1 g.). Yield 0.5 g. (74). [Found: C, 37.0; H, 3.9; 0; 9.9; Br, 12.6%. C20H24BrN404Re requires C, 36.9; H, 3.7; 0, 9.8; Br, 12.2%:] The compound was readily soluble in water and methanol and sparingly in ethanol and acetone, but insoluble in other common organic solvents. Dioxotetrabyridinerhenium(V) iodide monohydrate This compound was prepared in two mays. (a) The orange-red compound was prepared in a similar manner to the chloride and bromide, starting from oxodiiodoethoxobis(triphenylphosphine)rhenium(V) (1 g.). Yield 0.4 g. (60%). [Found: C, 36.0; H, 3.55 0, 7.5; 15 19.0j3. C20 11221N403Re requires C, 35.4; H, 3.3; 0, 7.1; I, 18.72:]

(b) The compound was precipitated from a solution of dioxotetrapyridinorhenium(V) chloride dihydrate (1 g.) in meter (25 ml.) by addition of a saturated solution 94. of potassium iodide. The precipitate was filtered off, mashed with a saturated aqueous solution of potassium iodide, then ethanol and diethyl ether, and dried in vacuo (25°0/0.1. mm.). Yield 0,5 g. (45fc). Found: C, 36.0; H, 3.3; 0, 6.9; I, 18.2.1. The salt was moderately soluble in water and methanol, sparingly soluble in ethanol and insoluble in other common organic solvents. Bis(dioxotetracyridinerhenium(V)Lhexachloroplatinate(IV) tetrahydrate An aqueous solution (20 m1.) of the corresponding chloride (0.5 g.) was treated with a small excess of a concentrated solution of hexachloroplatinic acid. The yellow crystals which separated are filtered off, washed with a little cold water, then ethanol and diethyl ether, and dried in vacuo (25°0/0.1 mm.) for 48 hrs. Drying at 100°C. caused gradual decomposition. Yield 0.5 g. (ca.90). [Foundz C, 31.1; H, 3.1; 0,

C4oH48C10808?-tRe, requires C, 31.0; H, 3.1; 0, 8.3%.] The compound was slightly soluble in water but insoluble in the common organic solvents. Dioxotetrapyridinerhonium(V) te.traphonvlborate An aqueous solution of the corresponding chloride was treated with an aqueous solution of sodium totraphenyl- borate. The pale yellow precipitate was filtered off, mashed thoroughly with water and dried in vacuo (25°C/ 95. 0.1 mm.) for 48 hrs. before analysis. [Found: C9 60.5; H5 4.7; 09 3.8%. C44H4013N402Re requires C9 61.9; H, 4.7; 0,3.8/.1 . The compound is insoluble in water but is readily soluble in acetone. Ebullioscopic measurements in anhydrous acetone gave a value corresponding to two monomeric ions. [Found: 450; Calculated: 4261 Hydroxoiodotetraparidinerhenium(V_Ltris(triiodide) Dioxotetrapyridinerhenium(V) chloride dihydrate (1 g.) was boiled under reflux with 45% hydriodic acid (25 ml.) for some hours until shining black crystals separated. They were filtered off, mashed thoroughly with mater and dried in vacuo (40°C/0.1 mm.) for 48 hrs. [Found: C9 13.2; H5 1.4; N5 3.1; 09 2.6; 19 69.6%. C202111040Re requires C9 13.6; H9 1.4; N2 3.1; 09 2.6; I9 The infra-red spectrum showed no pyridinium group, coordinated water or double-bonded oxygen. lAoxobis(ethylenediamine)rhenium(V) chloride dihydrate Oxodichloroethoxobis(triphenylphosphine)rhenium(V) vas suspended in ethanol (25 ml.) and ethylenediamine hydrate (2 ml.) was added. The mixture was boiled under reflux for 1 hr. The solid mas filtered off, dissolved in water, (20 ml.), and the solution filtered. The solution was poured into vigorously stirred ethanol (200 ml.). The pale yellow crystalline compound was filtered off, mashed thoroughly with ethanol and diethyl 96. ether and dried in vacuo (40°C/0.1 mm.). Yield 0.3 g. (400). Pound: C, 12.05 N, 13.39 0, 14.89 H5 4.7; Cl,

8.8%. C4H20u1N404Re requires C, 11.75 N, 13.75 0, 15.6; H, 4.99 Cl, 8.7,0:1 The compound mas slowly hydrolysed by water giving an almost white compound. The infra-red spectrum of this compound showed a strong broad peak at 906 am.-1, about the region normally associated with perrhenate or other oxides of rhenium. similar com-

pound has been reported by Russian workers (131) who

formulated it as en.Re03. We were not able to charac- terise the compound but the analyses fit the formulation quite closely. The chloride found may be an impurity as

on this formulation it corresponds to only 0.33 atom.

[Found: C, 8.55 H9 2.7; N, 8.8; 0, 17.6; Cl, 4.0.

C2H8N203110 requires C, 8.29 H, 2.7; N. 9.5; 0, 16.3% Dioxobis(ethylenediamine)rhenium(V) iodide

The corresponding chloride (1 g.) was dissolved in water (10 ml.) and a saturated solution of potassium iodide

(10 ml.) added. The solid was filtered off, mashed thoroughly ti ith ethanol and diethyl ether and dried in

vacuo (25°C/0.1 mm.). Yield 0.6 g. (500). [Found: C9

9075 H, 3.55 N, 12.29 1 9 27.5%. C411151N402Re requires C 9 10.39 H5 3.5; N, 12.0; I, 273/0.3 Bis(diVdroxobis(aIhy1cnediamine)rhonium(V)) tris(hexa-

chlorop1atinate(I11)

This was prepared by the method of Murmann (132). 97. D'ound: C, 5.0; H, 2.0; 09 3.5. Calculated for

CnH-310C118, N804Ptge2 C5 5.0; H, 1.9; 0, Oxohydroxobis(ethylenediamine)rhonium(V) diperchlorate This as prepared by the method of Murmann (132).

OFound: C, 9.5; H, 3.0; N, 10.7; 0, 28.0; C1049 36.9%. Calculated for C4H17012N4010Re: C, 8.9; H, 3.2; N, 10.4; 0, 29.7; 01049 37.0C;,11 Dihvdroxobis(ethvlenediaminalrhenium(V) diaerchlorate chloride The purple crystals of the previous compound (1 g.) more suspended in concentrated hydrochloric acid (10 ml.) and 60% perchloric acid (2 ml.) was added. The mixture was stirred vigorously throughout the whole reaction with a glass rod.' The purple crystals slowly dissolved and at the same time bright blue needle-like crystals were precipitated. When reaction was complete, the compound was filtered off, mashed thoroughly ti ith anhydrous ether and dried in vacuo (25°C/0.1 mm.). Yield 1 g. (ca. loop. LFound: C, 9.0; H, 2.8; N, 10.2; Cl (ionic), 6.3; 0, 26.4; 01049 34.3. 041118013N4010Re requires C, 8.4; H, 3.2; N, 9.8; Cl (ionic), 6.2; 0, 27.8; C1049 34.5a. Dioxobis(2:4-hropenedionato)molybdonum(VI) The compound was prepared by the method in Inorganic syntheses. (145). ound: C, 36.5; H, 4.4). Calcu- lated for C1oH10006: C, 36.8; H, 4.3%0] 98.

Oxodichloro(2Li=proanedionato)(triphenvlphosalhine)-

rheniumiy)

Oxodichloroethoxobis(triphenylphosphino)rhenium(V) (2 g.)

was dissolved in benzene (50 ml.) and 24-propanediono

added (2 m1.). The solution was boiled until it went

greenish and mas then immediately poured into a large

excess of 40°-60° petroleum ether (40o ml.). The mixture

was treated in one of two ways.

(a) The mixture was stirred vigorously and the precipi-

tate allowed to settle. If the supernate was still ap-

preciably green it was decanted off and allowed to stand

when green crystals of the compound separated. These

were hand picked from any other material left and re-

crystallised by slow evaporation of a benzene solution

of the material.

(b) The mixture was stirred vigorously and allowed to

stand overnight. The mixture was stirred vigorously and

allowed to stand until the green crystals had settled.

The supernate containing most of the yellow material

was decanted off. This procedure was repeated using fresh portions of 40°-60° petroleum until practically

all the yellow material was removed. The green crystals

were then hand picked from any remaining material and recrystalliscd by slow evaporation of a benzene solution.

The crystals were washed mith a little diethyl ether and 99. and dried in vacuo, (25°C/0.L mm.), in both methods (a) and (b). Yield 0.2 g. (ca. 100. [Found: C9 44.3; H9 3.8; P, 4.7; Cl, 12.0; 0, 7.4(/.; M9 610. C23H22C1203PRe

requires U9 43.5; 119 3.5; P9 4.9; Cl, 11.2; 09 7.6%; M9 6350 The compound, which uas diamagnetic in benzene solution (n.m.r.) was soluble in dichloromethane, benzene, and chloroform and acetone, sparingly soluble in ethanol and ether, and insoluble in petroleum ether and carbon tetrachloride. 0xodibromo(2:4-propanedionato)(triphonvlphosphine)- rhenium(V) This was prepared in a very similar manner to the above compound starting from oxodibromoethoxobis(triphonylphosphine)rhenium(V). Yield ca. 15%. [Found: C, 38.7; H, 3.1; Br, 2L.7h; M9 660. C23H22Br203PRe requires C9 38.2; H, 3.1; Br, 22.lcp; M9 723:.] The compound was diamagnetic and similar to the chloro-compound, but slightly more soluble in organic solvents. Oxodiiodo ganedionato)(triphonylphosphina)- rhenium(V) This compound was prepared in the above manner, starting from oxodiiodoothoxobis(triphenylphosphine)rhenium(V) but it has not been possible to prepare it pure yet, because of the very similar solubility to the other

product of the reaction. A sample about 50% pure has 100. been obtained, allowing a measurement of the Ro=0 stretching frequency. Oxodichloro(2:4-propanedionato)(phenyldiethylphosphine)- rhenium(V) This mas prepared in a similar manner to the above chloro- compound of triphenylphosphine. The compound was separated using method (b). Yield ca. 20. [Found: C, 33.8;

H, 4.0%. C15H22C1203PRe requires C, 33.5; H, 4.11. The compound, which vas diamagnetic, was very similar to the triphenylphosphine complex but was much more soluble in organic solvents. Dichloro(,14-propanedionato)bis( triphenylphosphine) - rhenium( III) Oxodichloroethoxobis(triphenylphosphine)rhenium(V) (2 g.) was dissolved in benzene (30 ml.) and 2:4-propanedione (2 ml.) added. The solution was boiled under reflux for about six hours and then allowed to cool. The solution was reduced to 15 ml. by evaporation in vacuo (2500/ 0.1 mm.). The orange-red crystals of the compound were filtered off, mashed with a little benzene and diethyl ether and dried in vacuo (25°C/0.1 mm.). Yield 0.5 g. (ca. 25).Found; C, 55.9, 55.7; H, 4.3, 4.4; P, 6.4, 2P2Re 6.9; 0, 4.0;01, 8.5, 8.0; M9 911. C41-- H37 C120 requires C, 55.9; H, 4.2; P, 7.0; 0, 3.6; Cl, 8.1; h, 881.] The compound as soluble in dichloromethane and 101. sparingly soluble in ethanol, benzene, and chloroform; it was slightly soluble in diethyl ether. It was insoluble in carbon tetrachloride and petroleum ether. The compound was paramagnetic. The magnetic moment is discussed in the text. The supernatant solution which was brown contained some tris(2:4-propanedionato)- rhenium(III) which crystallised out on further evaporation. ¶Found: C, 36.7; H9 3.72,;. Calculated for C15H2106Re: C, 36.0; H, Dibromo(2:4-bropanedionato)bis(triphenylphouhine)- rhenium(III) This was prepared in a similar manner to the above compound starting from oxodibromoethoxobis(triphenylphosphine)rhenium(V), and was obtained as orange crystals. Yield ca. 25k. [Found: G5 49.0; H9 3.9; Br, 17.0; 0, 4.0; P, 6.1g,. 041H37Br202P2Re requires C, 50.8; H9 3.9; Br, 16.5; 0, 3.3; P9 6.4.1 The compound was similar in properties to the chloro-compound, but was more soluble in organic solvents. Diiodo(2:4-probanedionato)bis(trichenylphoqphine)- rhenium(III) This compound was obtained as orange-brown crystals in a similar manner to the two previous compounds, but it was not completely pure, as shown by a small peak in the infra-red spectrum at 975 cm71 (an Re=0 stretch). The 102. analyses correspond to a mixture of about 90(/.,

(Pkt ) Ro(acac)I and lOch (1-Ph3)Re0I2(4,4Found; C9 3 2 2 45.0; H, 3.3; 1 9 24.0; P9 4.0; 09 3.3; M9 1000. 041H371202P2R0 requires 09 46.4; H9 3.5; 15 23.9; P, 4.6; 0, 3.0; Ni, 1063.] The compound was similar to the two previous compounds but more soluble in organic solvents. Dichloro(2;Ii-prooanedionato)bis(kbenyldiethylohosohine)- rhenium(III)

This was prepared in a similar manner to the above compounds starting from oxotrichlorobis(phenyldiethylphosphine)rhenium(V) and mas obtained as rod-orange crystals. Yield ca. 25%. EFoundo C9 43.8; H, 5.47;. C25H3701202P2Re requires C, 43.6, H, 5.4.] The compound was more soluble than the corresponding triphenylphosphine compound. "Maroon" rhenium oxide

Potassium hexachlororhenate(IV) (5 g.) was dissolved in water (100 ml,) and 2M sodium hydroxide solution (50 ml.) added. The solution was heated to boiling and allowed to stand overnight. The black precipitate was filtered off, mashed thoroughly with boiling vat- r (300 ml.) and dried in air (room temp.). A sample of the hydrated oxide was placed on

a match glass and heated in an oven at 185°0. for 48 hrs.

A purple-red (maroon) solid was obtained. The solid was • 103. practically diamagnetic. Rhenium in the oxide was determined by reduction in hydrogen at 400-500°C. Found:

Re, 82.7%. Re0 requires Re, 82.7%.] The material 2.45 was heated in air at 185°C. for one meek with no significant chang,:; in weight or composition. Found; Re, 82.7%.Q It uses found that the reaction would start at as lov as 120°C. in air. "Green" rhenium oxide A sample of the hydrated oxide, prepared as above, was spread on a match glass and heated fur 24 hours at 195°C. in air. A green solid was obtained. The solid vas paramagnetic at room temperature. fk-3ff. = ca. 2.5 B.M. [ound: Re, 81.5%. Re0 .67 requires Re, 81.476] Appendix 104. Abbreviations used in the text. diarsine o-phenylenebis(dimethylarsine) tetraarsine oxide bis(ethylenediphenylarsine)(ethylenediphenylarsine oxide) ursine

py pyridine Ph P triphenylphosphine 3 triphenylphosphine oxide Ph3PO o-phen o-phenanthroline Et ethyl Ph3As triphenylarsine Ph As0 triphenylarsine oxide 3 PEt2Ph phenyldiethylphosphine diphosphine 1:2-ethytenebis(diphenylphosphine) acac 2:4-propanedionato- en ethylenediamine T.H.F. tetrahydrofuran 105.

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156. Hopkins, Hurd, Tacbel. ibid. Vol. 1. P. 180. 157. Idem, ibid. Vol 1. p. 182. REPRINTED FROM CHEMISTRY AND INDUSTRY, 1962, p.40 Complexes of Rhenium(V) Oxytrichloride Ceoiin LAC

By C. J. L. Lock and G. Wilkinson

Inorganic Chemistry Research Laboratories, Imperial College, London, S. W.7

Two products, each of which were formulated as material for a variety of other preparations including bistriphenyl-phosphine rhenium(III) trichloride, have dihalides, carbonyls,' and ([(C6H5)311- 2ReCN RI } 1,5 been reported. One of them, A, was obtained by the and the same product, presumably, has also been used reduction of perrhenic acid by hydrochloric acid in in the preparation of hydrides by reduction.6 In ethanol in the presence of triphenylphosphine and was these cases either the nature of the resulting material or yellowish-green;' the other, B, obtained by chlorina- the reaction mechanism must now be reconsidered and tion of [(C61-15)3PReC13]2 in presence of excess tri- we have shown, for example, that the "dihalides," phenylphosphine in acetone, was purple red.2 An [(C6H5)3P]2ReX2, are in fact oxyhalide alkoxides, investigation of this discrepancy has shown that both [(C6H5)3P]2Re0X20C2H5 (X= Cl, Br, I) since they compounds were in fact wrongly formulated; both again show an Re=O stretching frequency at ca. contain oxygen, A being [(C6H 5)3P]2Re0C13 and B, 950 cm.-1 with a further band at 906 cm.-1 suggesting [(C61-15)3P0]2ReC13. In these compounds the the presence of an Re-O- bond which we have con- amount of oxygen is so small that it makes little firmed by direct ethoxyl analysis [Found: C, 49.2; difference to the analyses of the other elements. H, 4.5; Br, 16.5; 0C2H5, 4.87. Required for Further, direct oxygen analyses of phosphorus com- C38H35PO2Br2: C, 49.0; H, 3.8; Br, 16.1; 0C2H5, pounds by the standard organic procedure give high 4.89%]. results, damage to the quartz tube occurring,3 and The purple compound B shows no strong peaks in this procedure has shown the presence of oxygen in the Re=0 stretching region but has bands at M 685, phosphorus compounds which do not contain oxygen.4 740 and at 720 cm.-1; the latter is due to a co-ordinated The presence of oxygen can, however, he shown by triphenylphosphine oxide, and the spectrum of B is infrared spectra and by analogy with corresponding essentially identical with that of [(C6H5)3P0]2ReC13 compounds derived from triphenylarsine, where made by direct interaction of Re2C16 and triphenyl- direct oxygen analyses can be made, or directly from phosphine oxide. A similar triphenylarsine oxide the triphenylphosphine or arsine oxides. compound has also been made. The infrared spectrum of Freni and Valenti's compound A shows the strong peaks at 685 and 740 cm.-1 expected for a triphenylphosphine complex but Received November 8, 1961 in addition there is a very strong peak at 966 cm.-1 which is clearly assignable as an Re=O stretch.2 The References analyses and spectra, as well as the method of prepara- 1 Freni, M. & Valenti, V., J. inorg. nucl. Chem., 1961, 16, tion, thus agree with the stoicheiometry [(C6H5)3P]2- 240 2 Colton, R., Levitus, R. & Wilkinson, G., J. chem. Soc., Re0C13. No complexes of this type have been 1960, 4121 isolated previously and the oxytrichloride itself is 3 Oliver, F. H., in "Comprehensive Analytical Chemistry," unknown. Other complexes have now been made by Editors: C. L. Wilson & D. W. Wilson, Vol. IB, 1960, the same procedure,' a triphenylarsine derivative for p. 577. New York: Elsevier 4 Cuckney, Miss J., Microanalytical Laboratory, Imperial example being a green solid; analyses confirm the College, personal communication presence of oxygen [Found: C, 45.7; H, 3.7; As, 16.37; 5 Freni, M. & Valenti, V., Gazz. chim. ital., 1960, 90, 1445 CI, 11.24; 0, 1.82%. Required for C36H30As2 6 Malatesta, L., Freni, M. & Valenti, V., Angew. Chem., - 1961, 73, 273; Malatesta, L., "Advances in the Chemistry of Co- Re0C13: C, 46.9; H, 3.3; As, 16.27; Cl, 11.55; ordination Compounds. Proceedings of the 6th International 0, 1.74%]. Conference on Co-ordination Chemistry," Ed.: S. Kirschner Freni and Valenti have used A as the starting 1961, p. 475. New York: Macmillan Co. REPRINTED FROM CHEMISTRY AND INDUSTRY, 1963. pp. 333-334

Infrared, Spectra of trans-Dioxo Complexes of Transition Metals By N. P. Johnson, C. J. L. Lock and G. Wilkinson

Inorganic Chemistry Research Laboratories, Imperial College, London, S. W.7 During studies on rhenium complexes' we have A similar lowering of the metal-hydrogen stretching prepared several salts such as the tetraphenylborate frequency has been observed in octahedral complexes and hydrated halides of the dioxotetrapyridinorhenium containing a trans H-M-H group and this has been (V) ion, [Re02py4]÷. The infrared spectra of all related to the strong trans-effect of hydrogen as a these salts show no band in the region 900-1100 cm.-1 ligand.11 In compounds of the type (R3P)2ReOXY2 which has been considered2 to be characteristic for it appears that the Re=O stretching frequencies arc metal-oxygen double bond stretching frequencies,* lowered by strong trans-effect substituents, X, in the but they do have a single strong band at about 825 trans 0= Re—X grouping and the X-group is also very cm.-1. This band does not occur in other pyridine labile.1,5 Hence we suggest that the oxygen atoms in complexes4 and hence may be assigned as the Re=0 0 groups have a strong trans effect, which is in stretching frequency. In octahedral rhenium com- keeping with the ease of replacement of trans-C1 by plexes with only one Re=0 group present,1,5 e.g. —OEt in (Ph3P)2Re0C13,5 and the lowering of the (Ph3P)2Re0C1 3, the Re=O stretching frequencies are M=0 stretching frequencies in trans-dioxo groups is in the region 940-985 cm.-1. Hence we consider that hence understandable. It appears, further, that the the unusually low frequency found in salts of [Re02- region previously considered to be diagnostic for py4J+ is owing to the presence of a trans-dioxo group, M=0 stretching frequencies must now be extended 0= Re-=0. Other dioxo species which do not show downwards. bands in the 900-1100 cm.-1 region but which have a Received November 17, 1962 single strong band at lower frequencies arc, e.g. [Re02(CN)4]3— and [ReO2en2]+, which absorb at 780 cm.-1 and about 820 cm.-1 respectively. Although References 1 Lock, C. J. L. & Wilkinson, G., Chem. & Ind., 1962, 40; and no X-ray data are available on rhenium compounds, unpublished results the infrared spectrum of the [Re02en21+ group is 2 Barraclough, C. G., Lewis, J. & Nyholm, R. S., J. chem. Soc., much more similar to that of trans-[Coen2X2P- than 1959, 3552; cf. also Selbin, J., Holmes, L. H., Jr. & McGlynn, to cis-[Coen2X21+ in the diagnostic regions.6 However, S. P., Chem. & Ind., 1961, 746 structure 3 Barraclough, C. G., Bradley, D. C., Lewis, J. & Thomas, X-ray studies have indeed confirmed the trans I. M., J. them. Soc., 1961, 2601 for K2[0s02C14]1 and K2[0s02(OH)4].8 For this 4 Gill, N. S., Nuttall, R. H., Scaife, D. E. & Sharp, D. W. A., type of compound it had been earlier assumed that J. Inorg. nucl. Chem., 1961, 18, 79 oxygen atoms are trans to each other and the diamag- 5 Chatt, J. & Rowe, G. A., Chem. & Ind., 1962, 92; J. chem. netism of [0s02C1.4]2— and of [RuO2C14]2— explained Soc., 1962, 4019 6 Baldwin, M. E., ibid., 1960, 4369 in terms of ligand-field theory.9 Several osmyl 7 Kruze, F. H., Ada Cryst., 1961, 14, 1035 compounds have bands in the low region, e.g. Porai-Koshits, M. A., Atovmyan, L. 0. & Andrianov, [0s02(OH)4]2— at 790 cm.-1 and [0s02(CN)4]2— at U. G., Zhurnal Strukturnoi Khbnii, 1961, 2 (6), 743 1.10 9 Lott, K. A. K. & Symons, M. C. R., J. diem. Soc., 1960, 820 cm.- 973 *Metal-oxygen single bond stretching frequencies appear to to Griffith, W. P., ibid., 1962, 3248 be below ca. 625 cm.-1.3. 11 Chatt, J. & Hayter, R. G., ibid., 1961, 2605, 5507