Crystal structures of the Y3.33CuPb1.5X7 (XÂ Â =Â Â S, Se) compounds

The crystal structures of the Y3.33CuPb1.5X7 (X = S, Se) compounds were investigated using X-ray powder diffraction (space group Cm, Pearson symbol mC25.67): a = 1.30246(5) nm, b = 0.39421(2) nm, c = 1.20671(4) nm, β = 104.953(3)°, RI = 0.0872 (for Y3.33CuPb1.5S7) and a = 1.35675(7) nm, b = 0.40959(2) nm, c = 1.26026(6) nm, β = 104.661(2)°, RI = 0.0893 (for Y3.33CuPb1.5Se7). The crystal structures of the Y3.33CuPb1.5X7 (X = S, Se) compounds can be derived from the structures of the Y5X7 (X = S, Se) compounds. The positions of the Y atoms with trigonal prismatic coordination in the Y5S7 and Y5Se7 compounds correspond to the positions of the atoms of a statistical mixture M (Y + Pb) and Pb in the structures of the Y3.33CuPb1.5X7 (X = S, Se) compounds. Additional position of the Cu atoms with tetrahedral coordination exists in the structures of the Y3.33CuPb1.5X7 (X = S, Se) compounds compared with Y5S7 and Y5Se7.