The crystal structure of Bi-8(AlCl4)(2) and the crystal structure, conductivity, and theoretical band structure of Bi6Cl7 and related subvalent bismuth halides

The methods of preparation for Bi-8(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. Bi-8(AlCl4)(2) consists Of isolated AlCl4- anions and rather undistorted square-antiprismatic Bi-8(2+) clusters with an average Bi-Bi distance of 3.10 Angstrom. Relatively short intercluster Bi-Bi contacts of 3.90 Angstrom suggest weak bonding interactions between the Bi-8(2+) units. In contrast, the structure determination of Bi6Cl7 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 (1)(infinity)[Bi2Cl24+] 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 (1)(infinity)[Bi2Cl24+] 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.