Syntheses and structures of the quaternary copper tellurides K(3)Ln(4)Cu(5)Te(10) (Ln = Sm, Gd, Er), Rb(3)Ln(4)Cu(5)Te(10) (Ln = Nd, Gd), and Cs3Gd4Cu5Te10

Six quaternary alkali-metal rare-earth copper tellurides K(3)Ln(4)Cu(5)Te(1 0) (Ln = Sm, Gd, Er), Rb(3)Ln(4)Cu(5)Te(10) (Ln = Nd, Gd), and Cs3Gd4Cu5Te1 0 have been synthesized at 1123 K with the use of reactive fluxes of alkali -metal halides A Cl (A = K, Rb, Cs). All crystallographic data were collect ed at 153 K. These compounds crystallize in space group Pnnm of the orthorh ombic system with two formula units in cells of dimensions (A(3)Ln(4), a, b , c (Angstrom)): K3Sm4, 16.590(2), 17.877(2), 4.3516(5); K3Gd4, 16.552(4), 17.767(4), 4.3294(9); K3Er4, 16.460(4), 17.550(4), 4.2926(9); Rb3Nd4, 17.35 6(1), 17.820(1), 4.3811(3); Rb3Gd4, 17.201(2), 17.586(2), 4.3429(6); Cs3Gd4 , 17.512(1), 17.764(1), 4.3697(3). The corresponding R-1 indices for the re fined structures are 0.0346, 0.0315, 0.0212, 0.0268, 0.0289, and 0.0411. Th e three K(3)Ln(4)Cu(5)Te(10) structures belong to one structure type and th e Rb(3)Ln(4)Cu(5)Te(10) (Ln = Nd, Gd) and Cs3Gd4Cu5Te10 structures belong t o another one, the difference being the location of one of the three unique Cu atoms. Both structure types are three-dimensional tunnel structures tha t contain similar Ln/Te fragments built from LnTe(6) octahedra and CuTe4 te trahedra. The CuTe4 tetrahedra form (1)(infinity)[CuTe35-] and (1)(infinity )[CuTe23-] chains. The alkali-metal atoms, which are in the tunnels, are co ordinated to seven or eight Te atoms. (C) 2001 Academic Press.