Structure of a synthetic halogen sulfosalt, Cu3Bi2S3I3.

Cu(3)Bi(2)S(3)I(3) was crystallized during an attempt to synthesize Cu-Pb-Bi sulfosalts with iodine as the transport medium. The crystal structure was solved from a black needle-like crystal on a four-circle diffractometer with a CCD detector. The solution was obtained by direct methods and subsequent difference-Fourier syntheses. S and I atoms are arranged in a systematically distorted cubic eutaxy (close packing). Bi atoms have monocapped trigonal prismatic coordinations, while Cu atoms occupy coordination sites which vary from trigonal planar to distorted tetrahedral. A prominent feature is the distribution of Cu atoms over many closely spaced sites in the structure, the majority of them being only partly occupied, which strengthens the case for mobile Cu atoms during crystal growth at elevated temperatures. In this respect, Cu(3)Bi(2)S(3)I(3) represents an extreme example of a statistical distribution of Cu in the structure; a frequently observed property of this element in sulfosalts.