Syntheses, structures, physical properties, and electronic structures of KLn2CuS4 (Ln = Y, ND, Sm, Tb, Ho) and K2Ln4Cu4S9 (Ln = Dy, Ho)

Seven new quaternary metal sulfides, KY2CuS4, KNd2CuS4, KSm2CuS4, KTb2CuS4, KHo2CuS4, K2Dy4Cu4S9, and K2Ho4Cu4S9, were prepared by the reactive flux method. All crystallographic data were collected at 153 K. The isostructural compounds KLn(2)CuS(4) (Ln = Y, Nd, Sm, Tb, Ho) crystallize in space group Cmcm of the orthorhombic system with four formula units in cells of dimensions (Ln, a, b, c (Angstrom)): Y, 3.9475(9), 13.345(3), 13.668(3); Nd, 4.0577(3), 13.7442(10), 13.9265(10); Sm, 4.0218(4), 13.6074(14), 13.8264(14); Tb, 3.9679(5), 13.4243(17), 13.7102(18); Ho, 3.9378(3), 13.3330(11), 13.6487(11). The corresponding R, indices for the refined structures are 0.0197, 0.0153, 0.0158, 0.0181, and 0.0178. The isostructural compounds K2Dy4Cu4S9 and K2Ho4Cu4S9 crystallize in space group C2/m of the monoclinic system with two formula units in cells of dimensions (Ln, a, b, c (Angstrom), beta (degrees)): Dy, 13.7061(13), 3.9482(4), 15.8111(15), 109.723(1); Ho, 13.6760(14), 3.9360(4), 15.7950 (16), 109.666(2). The corresponding R-1 indices are 0.0312 and 0.0207. Both structure types are closely related three-dimensional tunnel structures. The tunnels are filled with bicapped trigonal-prismatically coordinated K atoms. Their anionic frameworks are built from LnS(6) octahedra and CuS4 tetrahedra. KLn(2)CuS(4) contains (1)(infinity)[CuS35-] chains of vertex-sharing tetrahedra and K(2)Ln(4)Cu(4)S(9) contains (1)(infinity)[Cu4S812-] chains of tetrahedra. K2Ho4Cu4S9 shows Curie-Weiss paramagnetic behavior between 5 and 300 K, and has an effective magnetic moment of 10.71mu(B) for Ho3+ at 293 K. Optical band gaps of 2.17 eV for KSm2CuS4 and 2.43 eV for K2Ho4Cu4S9 were deduced from diffuse reflectance spectra. A first-principles calculation of the density of states and the frequency-dependent optical conductivity was performed on KSm2CuS4. The calculated band gap of 2.1 eV is in good agreement with the experimental value. (C) 2003 Elsevier Inc. All rights reserved.