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

The methods of preparation for Bi8(AlCl4)2 and Bi6Cl7 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 Bi6Cl7 and related subvalent bismuth halides. – Bi8(AlCl4)2 consists of isolated AlCl4‐ anions and rather undistored square‐antiprismatic Bi82+ 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 Bi82+ units. In contrast, the structure determination of Bi6Cl7 implies that this structure should be regarded as being composed of discrete Bi95+ clusters and a polymeric BiIII–Cl anionic lattice including infinite, distorted α1[Bi2Cl24+] chains. According to the experimental and theoretical results, the Bi6X7 (X = Cl, Br) family of subvalent bismuth halide compounds are anisotropic semiconductors along the crystallographic c axis. The conductivity is mediated by the onedimensional α1[Bi2Cl24+] chains. These are interconnected with the Bi95+ 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.