Crystal structures of the R3.33CuPb1.5Se7 (RÂ =Â Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds

The crystal structures of the R3.33CuPb1.5Se7 (R = Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds (space group Cm, Pearson symbol mC25.67) were determined by means of X-ray powder diffraction: a = 1.3624(3) nm, b = 0.41144(8) nm, c = 1.2645(3) nm, β = 104.68(1)° (for Tb3.33CuPb1.5Se7); a = 1.3557(5) nm, b = 0.4091(1) nm, c = 1.2574(4) nm, β = 104.59(2)° (for Dy3.33CuPb1.5Se7); a = 1.35314(8) nm, b = 0.40819(2) nm, c = 1.25609(7) nm, β = 104.577(3)°, RI = 0.0797 (for Ho3.33CuPb1.5Se7); a = 1.35018(7) nm, b = 0.40693(2) nm, c = 1.25433(6) nm, β = 104.492(2)°, RI = 0.0845 (for Er3.33CuPb1.5Se7); a = 1.34584(7) nm, b = 0.40560(2) nm, c = 1.25083(6) nm, β = 104.342(3)°, RI = 0.0866 (for Tm3.33CuPb1.5Se7); a = 1.3425(2) nm, b = 0.40437(4) nm, c = 1.2484(1) nm, β = 104.381(8)° (for Yb3.33CuPb1.5Se7) and single crystal diffraction: a = 1.3404(2) nm, b = 0.40307(6) nm, c = 1.2475(2) nm, β = 104.36(1)°, R1 = 0.0438 (for Lu3.33CuPb1.5Se7). The crystal structures of the quaternary R3.33CuPb1.5Se7 (R = Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds can be derived from the structure of the binary Y5Se7 compound. The positions of the Y (R) atoms with octahedral coordination in the binary Y5Se7 compound and the quaternary R3.33CuPb1.5Se7 (R = Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds are similar. Every position of the Y atom with trigonal prismatic coordination in the Y5Se7 compound corresponds to two defect positions of the atoms of the statistical mixture M (R + Pb) or Pb in the structures of the R3.33CuPb1.5Se7 (R = Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds. Additional position of the Cu atoms with tetrahedral coordination exists in the structures of the quaternary R3.33CuPb1.5Se7 (R = Tb, Dy, Ho, Er, Tm, Yb and Lu) compounds when compared with Y5Se7.