Crystal structure of the R5CuPb3Se11 (R = Er, Tm and Yb) compounds

The crystal structures of the R5CuPb3Se11 (R = Er, Tm and Yb) compounds (space group Cmcm, Pearson symbol oC88-8) were determined by means of X-ray single crystal diffraction: a = 0.40710(8) nm, b = 1.3480(2) nm, c = 3.8092(7) nm, R1 = 0.0560 (Er5CuPb3Se11) and X-ray powder diffraction: a = 0.40582(3) nm, b = 1.3429(1) nm, c = 3.7979(2) nm, RI = 0.0878 (Tm5CuPb3Se11); a = 0.40487(3) nm, b = 1.33993(9) nm, c = 3.7876(2) nm, RI = 0.0917 (Yb5CuPb3Se11). R-centered octahedra, Pb-centered trigonal prisms and Cu-centered tetrahedra exist in the structures of these compounds. The crystal structure of the R5CuPb3Se11 (R = Er, Tm and Yb) compounds can be obtained by substitution of one trivalent R atom (Y) of Y6Pb2Se11 by one bivalent Pb atom and one monovalent Cu atom. This extra Pb atom is located in the position of the substituted R atom. Additional positions of the Cu atoms appear. The positions of remaining atoms are identical.