It may be formed by the reaction of bismuth oxide and hydrobromic acid.[1]
Bi2O3 + 6 HBr ⇌ 2 BiBr3 + 3 H2O
Bismuth tribromide can also be produced by the direct oxidation of bismuth in bromine.[1]
2 Bi + 3 Br2 → 2 BiBr3
Structure
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 groupP21/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.[3]
Reactivity
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. [BiBr6]3−, [Bi2Br10]4−, (BiBr− 4)n and (BiBr2− 5)n.[4]