Bismuth tribromide is an inorganic compound of bismuth and bromine with the chemical formula BiBr<sub>3</sub>.
It may be formed by the reaction of bismuth oxide and hydrobromic acid.
Bismuth tribromide can also be produced by the direct oxidation of bismuth in bromine.
Bismuth tribromide adopts two different structures in the solid state: a low-temperature polymorph ñ-BiBr<sub>3</sub> that is stable below 158 ðC and a high-temperature polymorph ò-BiBr<sub>3</sub> that is stable above this temperature. Both polymorphs are monoclinic, but ñ-BiBr<sub>3</sub> is in space group P2<sub>1</sub>/a whereas ò-BiBr<sub>3</sub> is in C2/m. ñ-BiBr<sub>3</sub> consists of pyramidal molecules whereas ò-BiBr<sub>3</sub> is polymeric and adopts the AlCl<sub>3</sub> structure. BiBr<sub>3</sub> is the only group 15 trihalide that can adopt both molecular and polymeric structures.
Bismuth bromide is highly water-soluble. It is a Lewis acid and accepts bromide ions to form monomeric and oligomeric anionic complexes (bromobismuthates), e.g. [BiBr<sub>6</sub>]<sup>3âÂÂ</sup>, [Bi<sub>2</sub>Br<sub>10</sub>]<sup>4âÂÂ</sup>, ()<sub>n</sub> and ()<sub>n</sub>.