Zur Polymorphie des Wismuttribromids*

Abstract

Abstract Bismuth tribromide exists in two modifications, α BiBr3 is stable below and β BiBr3 above 158°C. α BiBr3 is monoclinic (P21/a) with a = 842.9(1) pm, b = 984.8(2) pm, c = 675.6(1) pm and β = 109.65(1)°. The structure contains trigonal pyramidal BiBr3 molecules. Average distances are BiࢤBr = 266 pm (3×) and BiࢤBr = 332 pm (3×). The halogen atoms are ordered in a kind of compact packing, β BiBr3 crystallizes monoclinic (C2/m) with a = 724.9(2) pm, b = 1252.8(3)pm, c = 684.9(2)pm and β = 110.68(2)° and has the A1C13 structure type [Bi−Br = 282 pm (6×)]. BiBr3 is the only V. main group trihalide which can assume both molecular (α; molecule BiBr3 + 3 Bi−Br bonds) and a polymeric structure (β; 6Bi−Br contacts). The structures of the V. main group trihalides are compared. They are closely related by a common packing of their halogen atoms.