The Crystal Structure of Bi₈(AlCl₄)₂ and the Crystal Structure, Conductivity, and Theoretical Band Structure of Bi₆Cl₇ and Related Subvalent Bismuth Halides

Abstract

Abstract The methods of preparation for Bi 8 (AlCl 4 ) 2 and Bi 6 Cl 7 have been improved and the single crystal structures for these cluster compounds re‐investigated and re‐interpreted. In addition, conductivity measurements and band structure calculations using the tight‐binding approximation have been performed on Bi 6 Cl 7 and related subvalent bismuth halides. – Bi 8 (AlCl 4 ) 2 consists of isolated AlCl 4 ‐ anions and rather undistored square‐antiprismatic Bi 8 2+ clusters with an average Bi–Bi distance of 3.10 Å. Relatively short intercluster Bi–Bi contacts of 3.90 Å suggest weak bonding interactions between the Bi 8 2+ units. In contrast, the structure determination of Bi 6 Cl 7 implies that this structure should be regarded as being composed of discrete Bi 9 5+ clusters and a polymeric Bi III– Cl anionic lattice including infinite, distorted α 1 [Bi 2 Cl 2 4+ ] chains. According to the experimental and theoretical results, the Bi 6 X 7 (X = Cl, Br) family of subvalent bismuth halide compounds are anisotropic semiconductors along the crystallographic c axis. The conductivity is mediated by the onedimensional α 1 [Bi 2 Cl 2 4+ ] chains. These are interconnected with the Bi 9 5+ clusters, which are acting as electron reservoirs. The related BiX (X = Br, I) family of subvalent bismuth halides are shown to be anisotropic semiconductors in the crystallographic b direction.