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Home , Nitrogen fluoride, Xenon difluoride, Xenon hexafluoride

Reactions of Some Ammonium Fluorometalates with XeF2

Jože Slivnik+*, Branko Družina, and Boris Žemva Jozef Stefan Institute and+Faculty for Natural Sciences and Technology, Edvard Kardelj University, Ljubljana, Yugoslavia Dedicated to Prof. Dr. Drs. h. c. Oskar Glemser on the occasion of his 70th birthday Z. Naturforsch. 36b, 1457-1460 (1981); received May 7, 1981 Difluoride Reactions, Ammonium Fluorometalates, Hydrazinium Fluorometalates

The reactions between (NH^TiFe, (NH^ZrFe, (NfL^HfFe, (NELtfeVFe, (NH4)3CrF6, NH4MnF3, (NH4)3FeFe and excess were investigated. The listed am- monium fluorometalates react with xenon difluoride to form corresponding xenon(II) fluorometalates, monoammonium fluorometalates with metal in the same oxidation state, and ammonium fluorometalates with metal in higher oxidation state, respectively.

The reactions between binary and xenon following new compounds, not accessible by other difluoride or xenon , respectively, yield conventional methods, were isolated and charac- a series of xenon(II) or xenon(VI) fluorometalates. terized: XeFe • FeF3 [3], XeF6 • ZrF4, XeF6 • HfF4

We have investigated these reactions in detail [11], XeF6 • 2 AlFs and XeF6 • GaF3 [12]. This study succeeded to isolate and identify seven xenon(II) is still being continued. and thirteen xenon(VI) fluorometalates [1]. Following the same basic approach we extended Since in some cases the reaction between binary the investigations recently onto reactions between and did not proceed at xenon difluoride or xenon hexafluoride and am- all under the applied reaction conditions, we monium fluorometalates. supposed that the binary fluoride is not reactive enough and that the reaction might proceed if the Experimental binary fluoride would be available in a more Materials reactive form. Highly reactive, pure binary fluorides was prepared and purified in this labora- were prepared in this laboratory earlier by reacting tory as described elsewhere [13]. Its purity was 99 ± 0.5 vol%. Additional purification, mainly from hydrazinium fluorometalates with elemental fluo- oxygen, was performed by irradiation of liquefied rine [2]. fluorine with the near UV light at 77 K [14]. The It was expected, therefore, that the metal fluoride purity of so obtained fluorine was above 99.9 vol%. Xenon was supplied by l'Air Liquide (Paris, which is formed in situ during the reaction between France) in 99.5% purity (the balance was ). hydrazinium fluorometalates and xenon hexa- Xenon difluoride was prepared by photosynthesis fluoride should be in a highly reactive form and using near UV lamp [15]. The purity of xenon should consequently react immediately with excess difluoride was checked by IR spectrum of the xenon hexafluoride to form xenon(VI) fluoro- vapours and by the determination of its triple point. (NH4)2MF6 (M = Ti, Zr, Hf) were prepared by metalates. We checked our speculation in the reac- crystallization from the water solutions of cor- tion between N2HeFeF5 and xenon hexafluoride. responding fluorometallic acid and ammonium Indeed XeFö • FeF3 was isolated [3], a compound fluoride [16-18]. which could not be obtained by other, more conven- (NH4)3MF6 (M = V, Cr, Fe) were prepared by tional ways. This result encouraged us to initiate a crystallization of solutions obtained by dissolving of corresponding metal trifluoride trihydrate in water systematic study of the reactions between xenon solution of ammonium fluoride [19-21]. difluoride or xenon hexafluoride on one side and NH4MnF3 was prepared by reaction between hydrazinium(l -f) fluorometalates, hydrazinium- Mn(N03)2 • 4 H20 and ammonium fluoride in water (2-f) fluorometalates and metal fluoride adducts solution [22]. with hydrazine on the other side [4-10]. So far the General procedure Reactions were carried out in arc welded nickel or copper pressure and weighing vessels equipped with Teflon packed nickel valves. The volume of the reaction vessel was about 100 ml. Chemical analysis of the products:

Compound Calcd [%] Found [%]

NH4ZrF5 Zr 44.67 F 46.52 NIL* 8.81 Zr 43.9 F 46.0 NH4 8.5 NH4HfF5 Hf 61.23 F 32.59 XH4 6.18 Hf 61.7 F 31.9 NH4 5.9 (NH4)3VF8 V 19.82 F 59.16 NH4 21.02 V 19.6 F 55.4 NH4 20.3 NH4CrF4 Cr 35.62 F 52.05 NH4 12.33 Cr 34.4 F 50.2 NHi 10.2 NH4MnF4 Mn 36.89 F 51.03 NH4 12.08 Mn 35.7 F 50.5 NH4 11.8 NEUFeF4 Fe 37.27 F 50.72 NH4 12.01 Fe 37.1 F 50.5 NHj 11.3

They were tested hydrostatically up to 200 atm Mass spectra were recorded on a Nier type mass and were designed also for manipulating solid spectrometer with an inlet system for the analysis materials. All transfers of materials were carried out of gases. either in the atmosphere of a dry box or by distilla- tion under vacuum in a well dried apparatus. Results and Discussion In a typical run 3 to 6 mmoles of ammonium The reactions between (NH4)2TiF6, (NH4)2ZrF6, fluorometalate was weighed into reaction vessel and dried by pumping upon in a dynamic vacuum for (NH4)2HfF6, (NH4)3VF6, (NH4)3CrF6, NH4MnF4, 12 h. Then a corresponding amount of xenon di- (NH4)3FeFe and excessive xenon difluoride were fluoride was added by sublimation. The vessel was investigated. The listed ammonium fluorometalates then thermostated at predetermined temperature react with xenon difluoride in a three different for several hours. After the reaction was completed, modes as follows: the reaction products were separated by fractional sublimation, isolated and identified. Volatiles at 1. Ammonium fluorometalate is completely fluo- 77 K, 193 K, 233 K and at room temperature were rinated by xenon difluoride to corresponding characterized by mass spectrometry and infrared spectroscopy. Solids were identified by chemical binary fluoride which reacts further with excess analysis, X-ray powder diffraction patterns, infra- of xenon difluoride to form correspondings xenon- red and Raman spectroscopy and magnetic suscep- (II) fluorometalate. tibility measurements. The stoichiometry of the reactions was followed throughout of experiment by 2. Tri- or di-ammonium fluorometalate is only weighing of all reactants and products to ± 5 mg. partially fluorinated by xenon difluoride to form monoammonium fluorometalate with the metal General apparatus and techniques in the same oxidation state. Raman spectra were recorded using a Spex 1401 3. Only metal in ammonium fluorometalate is double monochromator. As exciting radiation, the oxidized while the rest of the compound does not 515.5 nm line of an Ar+ laser or 647.1 nm of a Kr+ laser (Coherent Radiation) were used. Powdered change. samples were loaded into quartz cappilaries in a dry The reaction between (NH4)2TiF6 and xenon box temporarily plugged with Kel-F grease and sealed off by a small flame outside the dry box. difluoride belongs to the first group: Raman spectrum of (NH4)3VF8: 612(100), 596(83), 453 K 490(9), 342(96), 310(57), 270(76), 216(11), 188(9) (NH4)2TiF6 + nXeFa cm-1. several hours IR spectra were recorded using Perkin Elmer 521 XeF2 • TiF4 + *N2 + 2(1—x)NF3 + and Zeiss UR-20 spectrometers over the range 400 to 4000 cm-1. The sample was finely powdered and 8 HF + 3(2—x)Xe + n-(7—3z)XeF2 dusted onto chloride plates sandwiched in a n > 10, a: >0.7. leak tight brass holder. The reaction between (NH4)2TiFe and xenon di- X-ray powder photographs were obtained by the Debye Scherrer method on ENRAF (Delft, Holland) fluoride starts somewhere around 413 K but is very using monochromatized CuK<* radiation. slow. Even at 433 K with periodic pumping away In the case of known compounds X-ray powder of all volatile reaction products it takes several days, photographs were compared with the data from before the reaction is completed. Normally the ASTM tables. Finely powdered samples were sealed in 0.5 mm thin walled quartz capillaries as described reaction was carried out at 453 K. Obviously the under Raman spectra. related hydrazinium(2+) compound N2HeTiF6 is much more reactive. It reacts with xenon difluoride hedra of VF6-, appears at 660 cm-1 [25]. The already at 393 K forming XeF2 • TiF4. corresponding band in the Raman spectrum of our Interestingly enough, also some tri- compound is at 612 cm-1 indicating higher coordina- fluoride was obtained during the reaction. This is, tion number of fluorine around vanadium than six. as far as we know, the first chemical reaction where The compound decomposes in X-ray beam and it was prepared by the reaction turns very quickly from a white colour with a pink with xenon difluoride. cast to a green colour. This behaviour also rules out The reactions in the analogous systems the potential possibility of having a mixture of

(NH4)2ZrF6/XeF2 and (NH4)2HfF6/XeF2 belong to ammonium fluoride and NHiVFe as the reaction the second group: product. Both components are white and very stable in X-ray beams. Quite interesting is also 423 K (NH4)2MF6 + nXe F2 • the comparison with the analogous reaction of 36 h (N2H5)3VF6 and xenon difluoride. In this case

NEUMFs + 0.5 N2 + 4 HF + 1.5 Xe + NH4VFe [25] was obtained besides of nitrogen,

(n— 1.5)XeF2 , xenon and excess of xenon di- n >6, M = Zr, Hf. fluoride. It should be mentioned here that in this case ammonium hexafluorovanadate(III) and hy- Also in this case the reaction proceeds at the tem- drazinium hexafluorovanadate(III) appear to be perature around 423 K but only to NH4ZrF5 [22] approximately equally stable. The reason for this is and NELiHfFs [23], respectively. Both formed com- that vanadium is in 3 + oxidation state what is not pounds are very stable and do not react further the stable oxidation state of vanadium in xenon(II) with excess of xenon difluoride even at 473 K. fluorovanadates consequently the oxidation of the The most interesting reaction in the investigated metal takes place. At higher temperatures (about series of ammonium fluorometalates is the reaction 400 K or higher) the reaction between (N2H5)3VF6 between (NH4)3VFE and xenon difluoride: or (NH4)3VF6 and xenon difluoride proceeds in both 343 K cases to XeF2 • VF5. (NH4)3VF6 + wXe F2 • several days Reactions between NH4MnF3, (NH4)3CrF6 and (NH4)3FeF6 and xenon difluoride yield correspond- (NH4)3VF8 + Xe + (n—l)XeF2 ing NILIMF4 compounds. All three compounds are n >8. isomorphous as shown by X-ray diffraction patterns. The volatiles which were pumped away after reac- tion, were only pure xenon and excess of xenon 333 K NH4MnF3 + wXe F2 difluoride as shown by mass spectrometry and several hours infrared spectroscopy. Neither nitrogen, nor nitrogen NH4MnF4 [26] + 0.5 Xe + (n — 0.5)XeF2 trifluoride or any other nitrogen fluoride were found n >6 in volatiles. The amount of evolved xenon was equivalent to the oxidation of V3+ to V5+ by xenon 393 K (NH4)3CrF6 + nXeF2 difluoride. As shown by the magnetic susceptibility several hours measurements (NH4)3VFs is diamagnetic what is NH4CrF4 [27] + N2 + 8 HF + 3 Xe + also the evidence that vanadium was oxidized to (n—3)XeF2 the 5 + oxidation state. n > 7 The formation of VFs3- anion should be very unlikely but some of the experimental results 393 K (NH4)3FeF6 + wXeF2 collected so far indicate vanadium atom has co- several hours ordination of fluoride above six. Xenon di- NH4FeF4 [28] + N2 + 8 HF -f 3 Xe + fluoride is electrophylic agent, therefore we would (n—3)XeF2 expect its attack on the anion rather than on a n > 7 cation.

The symmetrical (V-F) stretching mode in Raman It is somewhat surprising that NHiMnF3 is spectrum of NH4VFe, which contains isolated octa- oxidized to NH4MnF4. The product formed at analogous reaction between (N2Hs)2MnF4 and xenon starting compound is the same or higher than the difluoride would namely suggest formation of usual oxidation state of a metal in corresponding NH4MnF5 [25] specially so since Mn4+ is the only xenon(II) fluorometalates {e.g. Ti4+, Zr4*, Cr4*, V5+ known oxidation state in the xenon(II) and etc.). If the oxidation state of a metal in the starting xenon(VI) fluorometalates. Interestingly enough, compound is lower than already mentioned {e.g. the reaction between NH4MnF3 and xenon hexa- Mn2+, V3+) than the reactivity of such an ammonium fluoride proceeds to the formation of fluorometalate is comparable with the reactivity of NH4+XeF5+MnF62- [29]. the corresponding hydrazinium fluorometalate. This Ammonium hexafluorochromate(III) and -ferrate- system offers a convenient way for the syntheses of (III) reacted with xenon difluoride according to our ammonium fluorometalates with a metal in higher expectation. NH4CrF4 was obtained also by the oxidation state. reaction of hydrazinium fluorochromate(III) with xenon difluoride, while in a similar reaction N2H6FeF5 yielded iron trifluoride. This work was financed through the Research As expected, ammonium fluorometalates react Community of Slovenia. The authors are indebted with xenon difluoride less readily than the cor- to Mrs. A. Rahten for preparation of numerous ammonium fluorometalates, Miss B. Sedej did the responding hydrazinium fluorometalates. This is analytical work and Dr. H. Leskoväek recorded specially true if the oxidation state of a metal in the mass spectra.

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