(Cu2MnS4)-S-IV (M-IV = Si, Ge, Sn) - analysis of crystal structures and tetrahedra volumes of normal tetrahedral compounds

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 Pmn2(1) in a wurtzite type superstructure. The refinement Of Cu2MnSiS4 converged to R = 0.0214 and wR2 = 0.0477. The redetennination 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 (4) over bar 2m, 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.