Die trikline Kristallstruktur von Ag2Bi2S3Cl2: Pseudosymmetrie und Zwillingsbildung

Ruby‐red crystals of Ag₂Bi₂S₃Cl₂ were synthesized from AgCl and Bi₂S₃ by cooling a melt from 770 K to room temperature. X‐ray diffraction on powders and single‐crystals revealed a triclinic crystal structure with special lattice constants (P &1macr; (No. 2), a = 1085.0(2), b = 717.2(1), c = 1137.6(1) pm, α = 89.80(1)?, β = 74.80(1)?, γ = 87.81(1)?). In the structure [Bi^IIIS₃Cl₄] polyhedra form 2[BiS_3/2Cl_4/4]^‐ double‐layers by sharing common faces and edges. The silver(I) cations between the layers are coordinated either octahedrally by sulfide ions or tetrahedrally by sulfide and chloride ions. The deviations from the monoclinic space group P 1 2₁/c 1 are small and induce twinning along [010]. Further pseudosymmetry is based on the stacking of layer packages with the symmetry of the layer group P (2/c) 2₁/c 2/b.