Bi 5 3+ ‐Polykationen in geordneten und plastischen Kristallen von Bi 5 [AlI 4 ] 3 und Bi 5 [AlBr 4 ] 3

Bi 5 3+ Polycations in Ordered and Plastic Crystals of Bi 5 [AlI 4 ] 3 and Bi 5 [AlBr 4 ] 3 Dark‐red air‐sensitive crystals of pentabismuth‐tris(tetrabromoaluminate) Bi 5 [AlBr 4 ] 3 and black crystals of Bi 5 [AlI 4 ] 3 have been crystallized from melts of Bi, Bi X 3 and Al X 3 ( X = Br, I). X‐ray diffraction on a single crystal of Bi 5 [AlI 4 ] 3 ( T = 293(2) K; space group Pnma ; a = 2143.6(3) pm, b = 1889.1(1) pm, c = 811.74(5) pm) revealed an ordered packing of Bi 5 3+ trigonal bipyramids and [AlI 4 ] − tetrahedra that corresponds to the PuBr 3 structure type. Contrary to the so far known Bi 5 3+ polycations with accurate D 3h symmetry, the bismuth cluster found in Bi 5 [AlI 4 ] 3 holds only C s symmetry. The room temperature structure of the tetrabromoaluminate Bi 5 [AlBr 4 ] 3 , which is related to the AuCu 3 type, shows a dynamic disorder of the Bi 5 3+ polycations ( T = 293(2) K; space group $Fm{\bar 3}c$ ; a = 1766.2(3) pm). Slight cooling induces the transition into an ordered rhombohedral phase isostructural to Bi 5 [AlCl 4 ] 3 ( T = 260(2) K; space group $R{\bar 3}c$ a = 1241.5(8) pm, c = 3041(2) pm).