Niobium Pentabromide, NbBr₅

Niobium Pentabromide, NbBr₅, is the only bromine compound of niobium hitherto prepared. It is obtained by the action of bromine vapour on the coarsely powdered metal, or on a mixture of niobium pentoxide and carbon in the absence of air. In the latter case some of the oxybromide is also formed. Niobium pentabromide is a fine, purple-red powder, very similar to red phosphorus in appearance. The fused substance forms garnet-red prisms. On being strongly heated it becomes yellow, and volatilises. It melts at about 150° C., and distils undecomposed in an inert atmosphere at about 270° C. It can be distilled unchanged in an atmosphere of nitrogen or carbon dioxide. It is very hygroscopic, hydrolyses rapidly in damp air, and is decomposed by water with a hissing noise and considerable evolution of heat into niobic acid and hydrobromic acid. It is soluble in absolute alcohol and in dry ethyl bromide.