Bismuth tribromide

Bismuth tribromide is an inorganic compound of bismuth and bromine with the chemical formula BiBr₃.

Preparation

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 α-BiBr₃ that is stable below 158 °C and a high-temperature polymorph β-BiBr₃ that is stable above this temperature. Both polymorphs are monoclinic, but α-BiBr₃ is in space group P2₁/a whereas β-BiBr₃ is in C2/m. α-BiBr₃ consists of pyramidal molecules whereas β-BiBr₃ is polymeric and adopts the AlCl₃ structure. BiBr₃ 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, e.g. ³⁻, ⁴⁻, _n and _n.