Syntheses and Structures of the Quaternary Copper Tellurides K3Ln4Cu5Te10 (Ln=Sm, Gd, Er), Rb3Ln4Cu5Te10 (Ln=Nd, Gd), and Cs3Gd4Cu5Te10

Six quaternary alkali-metal rare-earth copper tellurides K3Ln4Cu5Te10 (Ln=Sm, Gd, Er), Rb3Ln4Cu5Te10 (Ln=Nd, Gd), and Cs3Gd4Cu5Te10 have been synthesized at 1123 K with the use of reactive fluxes of alkali-metal halides ACl (A=K, Rb, Cs). All crystallographic data were collected at 153 K. These compounds crystallize in space group Pnnm of the orthorhombic system with two formula units in cells of dimensions (A3Ln4, a, b, c (?)): 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, 17.356(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 R1 indices for the refined structures are 0.0346, 0.0315, 0.0212, 0.0268, 0.0289, and 0.0411. The three K3Ln4Cu5Te10 structures belong to one structure type and the Rb3Ln4Cu5Te10 (Ln=Nd, Gd) and Cs3Gd4Cu5Te10 structures belong to another one, the difference being the location of one of the three unique Cu atoms. Both structure types are three-dimensional tunnel structures that contain similar Ln/Te fragments built from LnTe6 octahedra and CuTe4 tetrahedra. The CuTe4 tetrahedra form 1[CuTe5-3] and 1[CuTe3-2] chains. The alkali-metal atoms, which are in the tunnels, are coordinated to seven or eight Te atoms.