Vanadium fluoride, anhydrous

Since fluorine is difficult to prepare and manipulate, the anhydrous fluorides and oxyfluorides are prepared by the action of anhydrous hydrogen fluoride on other halides or oxyhalides of vanadium.1... 

Vanadium Tetrafluoride, hypovanadic fluoride, VF4, is produced by the action of anhydrous hydrogen fluoride on the corresponding chlorine compound, VC14, at temperatures from —28° to 0° C. It is an extremely deliquescent brown powder which readily undergoes hydrolysis with water, so that it does not give rise to double salts as in the case of the trifluoride. Its density at 23° C. is 2 9749. It decomposes above 325° C., yielding a mixture of the pentafluoride and the trifluoride 1... 

Vanadium Tetrafluoride. VF4 is formed along with VF5 and VF3 in the fluorination of metallic vanadium and the difference in volatilities of the three fluorides allows their separation by fractional sublimation. It can also be prepared by treatment of VCI4 with anhydrous HF in an inert solvent such as CCI3F at -78 °C. Pure VF4 is a bright green hygroscopic solid, which disproportionates at 100 °C to VF5 and VF3. Its structure consists of octahedrally coordinated VFg units linked... 

Pure anhydrous vanadium(III) fluoride is more conveniently prepared by the thermal decomposition, in an inert atmosphere, of ammonium hexafluorovanadate(III), the latter being formed by the fusion of ammonium hydrogen fluoride with vanadium (III) oxide. Long and Wilhelm were unsuccessful in their efforts to prepare vanadium(III) fluoride by these reactions their product became oxidized since it was not protected by an inert atmosphere. Also, there is evidence that these investigators started with impure vanadium (III) oxide. The procedure described below employs an inert atmosphere for the decomposition of the hexafluorovanadate. 

Previously, ammonium hexafluorovanadate (III) has been obtained only from aqueous solution. Its preparation in molten ammonium hydrogen fluoride has the advantage that it yields a product which is anhydrous. Aqueous preparations of ammonium hexafluorovanadate (III) tend to have sorbed moisture, which, during the decomposition, could through hydrolysis contaminate the vanadium(III) fluoride with oxide. 

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