Thomas Bernert

The system Cu3AsS4–Cu3SbS4 and investigations on normal tetrahedral structures

Abstract In order to develop a novel model to predict if a so called normal tetrahedral compound crystallizes in a wurtzite- or sphalerite superstructure type, the system Cu3AsS4–Cu3SbS4 was reinvestigated. A solid solution series was prepared and the mixed crystals were characterized by powder X-ray techniques. The crystal structures of Cu3As0.330Sb0.670S4, Cu3As0.736Sb0.264S4, and Cu3AsS4 were refined from single crystal X-ray data. The refinements converged to R = 0.0209, wR2 = 0.0484 (Cu3As0.330Sb0.670S4, 201 unique reflections, 15 parameters), R = 0.0235, wR2 = 0.0596 (Cu3As0.736Sb0.264S4, 218 reflections, 15 parameters), and R = 0.0241, wR2 = 0.0669 (Cu3AsS4, 721 reflections, 45 parameters). Z is 2 for all compounds. The volumes of the tetrahedra [MS4] were calculated for the investigated compounds. In addition, the corresponding data were calculated for further solids from literature data. The volumes of the tetrahedra are used to separate compounds with a sphalerite type anion arrangement from compounds with hexagonal packed anions. A closer inspection of the tetrahedra volumes reveals a greater variation for one given material in the case of wurtzite type superstructures than for sphalerite type superstructures. A critical difference in the tetrahedra volumes is derived from these data.

Cu2MnMIVS4 (MIV = Si, Ge, Sn) — analysis of crystal structures and tetrahedra volumes of normal tetrahedral compounds

Abstract The crystal structures of the normal tetrahedral compounds Cu2MnSiS4, Cu2MnGeS4, and Cu2MnSnS4 are presented. The structures were refined from single crystal X-ray data. Cu2MnSiS4 and Cu2MnGeS4 crystallize in the space group Pmn21 in a wurtzite type superstructure. The refinement of Cu2MnSiS4 converged to R = 0.0214 and wR2 = 0.0477. The redetermination of Cu2MnGeS4 converged to R = 0.0281, wR2 = 0.0739. The tetrahedra volumes of the coordination polyhedra of the cations in these compounds are calculated and compared with those of Cu2MnSnS4 (redetermination, spacegroup I-42m, sphalerite type superstructure, R = 0.0146, wR2 = 0.0425). In the wurtzite type structures the tetrahedra volumes differ significantly for different cations while they differ only in a small range in the sphalerite type structure.

catena-Poly[[dipyridine­nickel(II)]-trans-di-μ-chlorido] from powder data

The asymetric unit of the title compound, [NiCl2(C5H5N)2]n, contains two NiII ions located on different twofold rotational axes, two chloride anions and two pyridine rings in general positions. Each NiII ion is coordinated by two pyridine rings, which form dihedral angles of 33.0 (2) and 11.0 (2)° for the two centers, and four chloride anions in a distorted octahedral geometry. The chloride anions bridge NiII ions related by translation along the short b axes into two crystallographically independent polymeric chains.