OSMIUM OXIDE PENTAFLUORIDE

OsOF5 OSMIUM OXIDE PENTAFLUORIDE 18125.3278 -4.6581E+05 -7.4493E+03 6.8812E+00... 

The iodine and technetium analogues of osmium oxide pentafluoride presumably can exist. Even ruthenium oxide... 

The Preparation and Some Physical Properties of Osmium Oxide Pentafluoride, OsOF ... 

In order to better understand the factors which are involved in limiting the oxidation state of osmium, a search for high valent oxyfluorides was undertaken. In particular, since six-co-ordinate osmium occurs in the readily formed hexafluoride, both osmium dioxide tetra-fluoride and osmium oxide pentafluoride appeared possible. 

Preparation of Osmium Oxide Pentafluoride.—Osmium oxide pentafluoride was made in several ways, (a) Osmium metal was heated in a stream of oxygen and fluorine (1 2 v/v). The reaction was carried out in a quartz tube with the osmium in a nickel boat, and was initiated by the heat from a small flame. Once started, the reaction sustained itself. The product, which was caught in traps at —183°, was a mixture of an emerald green solid and a pale yellow, more volatile, solid. The difference in volatility of the components of the mixture permitted their separation by trap to trap sublimation under reduced pressure, from a trap held at —16° to receivers cooled with liquid nitrogen. The emerald green solid was retained in the —16° trap. The more volatile, yellow, component proved, from its infrared spectrum, to be osmium hexafluoride. The emerald green solid, m. p. 59-2°, established by infrared spectroscopy, to be free of OsFj, amounted to —50% of the product. 

It was assumed that OsO,F, would be colourless and diamagnetic and phjrsically similar to OsOF, and OsF,. The infrared spectra of osmium oxide pentafluoride samples taken from a variety of preparations were identical with one another. The entire product from one oxyfluorination of osmium metal was subjected to infrared examination. The bulk of the sample in a Monel trap, was isolated from the gas cell by a Hoke valve. After each vapour sample had been scanned it was discarded and a new sample of vapour admitted. This was repeated exhaustively. All the spectra were interpretable in terms of OsF OsOF OsO and traces of HF, CF, SiF and CO,. Two independent magnetic measurements on samples of OsOF one from an oxjrfluorination of the metal and the other from the fluorination of the dioxide gave magnetic susceptibility values equal within the usual experimental uncertainty. Furthermore the magnitude of the susceptibility was consistent with pure OsOF,. 

Physical Aspects.—Osmium oxide pentafluoride was of special interest since it was, at the time of its discovery, the only unambiguously heptavalent osmium compound. It remains the sole heptavalent osminm compound, available in molecular form, under normal... 

The formation of osmium oxide pentafluoride is noteworthy on two counts. First, it represents an unusual osmium valence and secondly, it is evidently preferred to osmium dioxide tetrafluoiide which is an alternative product of the osmium-oxygen-fluorine system. The latter would, of course, involve all the osmium valence electrons in bonding and molecular species OsO,F, again involves osmium in only six-co-ordination. There is no evidence, however, that this compound can be formed, either by the oxyfluorination of osmium, or by the fluorination of the dioxide. 

---