The crystal structures of R3CuGeS7 (R = Ce-Nd, Sm, Gd-Dy and Er)

Abstract Crystal structures of R 3 CuGeS 7 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy and Er) (La 3 CuSiS 7 structure type, space group P 6 3 , Pearson symbol hP24 ) were determined by means of X-ray single crystal diffraction ( a  = 1.0225(1) nm, c  = 0.58350(7) nm, R 1  = 0.0213 for Ce 3 CuGeS 7 ; a  = 1.0168(1) nm, c  = 0.58223(7) nm, R 1  = 0.0284 for Pr 3 CuGeS 7 ; a  = 1.0123(1) nm, c  = 0.57942(7) nm, R 1  = 0.0240 for Nd 3 CuGeS 7 ) and X-ray powder diffraction ( a  = 1.00144(1) nm, c  = 0.57714(1) nm, R Bragg  = 0.0968 for Sm 3 CuGeS 7 ; a  = 0.99428(1) nm, c  = 0.57592(1) nm, R Bragg  = 0.0863 for Gd 3 CuGeS 7 ; a  = 0.98863(1) nm, c  = 0.57535(1) nm, R Bragg  = 0.0838 for Tb 3 CuGeS 7 ; a  = 0.98371(3) nm, c  = 0.57552(3) nm, R Bragg  = 0.0802 for Dy 3 CuGeS 7 ; a  = 0.97415(1) nm, c  = 0.57835(1) nm, R Bragg  = 0.0709 for Er 3 CuGeS 7 ). The structures are built up from three-dimensional network of RS 8 distorted square antiprisms sharing edges, consolidated by GeS 4 tetrahedra and CuS 3 triangles sharing edges with the antiprisms.