Low-temperature ordering in the cluster compound (Bi8)Tl[AlCl4]3

Abstract

The reaction of Bi, BiCl3, and TlCl in the ionic liquid [BMIm]Cl·4AlCl3 (BMIm = 1-n-butyl-3-methylimidazolium) at 180 °C yielded air-sensitive black crystals of (Bi8)Tl[AlCl4]3. X-ray diffraction on single crystals at roomtemperature revealed a structure containing 1 ∞ [Tl(AlCl 4)3]2- strands separated by isolated Bi82+ square antiprisms. The thallium(I) ion is coordinated by twelve Cl- ions of six [AlCl4]- groups, resulting in a chain of face-sharing [TlCl12]11- icosahedra. The Bi82+ polycation is disordered, simulating a threefold axis through its center and overall hexagonal symmetry (space group P63/m). Slowly cooling the crystals to 170 K resulted in increased order in the Bi8 cluster orientations. An ordered structure model in a supercell with a' = 2a, b' = 2b, c' = 3c and the space group P65 was refined. The structure resembles a hexagonal perovskite, with complex groups in place of simple ions.