Osmium oxide pentafluoride is an inorganic compound with the chemical formula OsOF5. It is a paramagnetic emerald green solid, notable for being a heptavalent osmium compound stable in molecular form under normal temperature and pressure.
Structure It is dimorphic, forming orthorhombic crystals and transitioning to a cubic disordered phase at 32.5 °C. OsOF5, in its high temperature form, is indistinguishable crystallographically from OsF6.
Preparation Osmium oxide pentafluoride can be prepared in several ways.
From elements It can be prepared by heating osmium metal in a stream of oxygen and fluorine (1:2 v/v). The reaction is self-sustaining after initiation by heat. The resulting product mixture is captured in a cold trap and the osmium hexafluoride byproduct is separated by difference in volatility. The yield is reported to be 50%.
Fluorination of osmium dioxide Anhydrous osmium dioxide is reacted with a slight excess of fluorine in a closed monel can. The product is separated from the osmium hexafluoride byproduct using the aforementioned technique with a yield of over 90%. 2 OsO2 + 5 F2 → 2 OsOF5 + O2
Other fluorinating agents OsO2 is fluorinated to OsOF5 by ClF3 with quantitative yields at ambient temperature.
OsO4 is fluorinated into a mixture of OsO3F2 and OsOF5 by ClF3 at ambient temperature. The formation of OsOF5 corresponds to a reduction of osmium from +8 to +7.
Related compounds Other oxide fluorides of osmium are known including: OsO3F2, OsO2F3, and OsOF4. There is some evidence for the existence of OsO2F2.
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