Vanadyl Dibromide, VOBr₂

Vanadyl Dibromide, VOBr₂, is obtained by passing bromine vapour or, preferably, a mixture of sulphur bromide, S₂Br₂, and bromine over a mixture of vanadium pentoxide and sulphur at a red heat; the product is heated in vacuo at 240° C., whereupon the vanadyl dibromide is obtained as a yellow powder. An alternative method of preparation consists in heating vanadium oxytribromide, VOBr₃, to 180° C. Vanadyl dibromide is no doubt present in the blue solution which results when hypovanadic oxide, VO₂, is dissolved in hydrobromic acid.

Vanadyl dibromide is a hygroscopic, unstable compound. It dissolves in water to give a blue solution. On being heated in air it forms vanadium pentoxide; in vacuo at 240° C. it partly sublimes and partly decomposes, with evolution of bromine and formation of a violet residue of vanadium oxymonobromide, VOBr. The dielectric constant has been investigated.

No double salts of vanadyl dibromide have been prepared.