STRUCTURE OF TL2SNTE5

Dithallium tin pentatelluride, M(r) = 1165.4, tetragonal, I4/mcm, a = 8.306 (2), c = 15.161 (5) angstrom, V = 1045.9 (8) angstrom3, Z = 4, D(x) = 7.40 Mg m-3, lambda-(Mo K-alphaBAR) = 0.7107 angstrom, mu = 47.09 mm-1, F(000) = 1888, T = 294 K, final R = 0.041 for 236 independent observed reflections. The structure of Tl2SnTe5 consists of SnTe4 tetrahedra (T), TeTe4 square-planar units (S) and two types of Tl atoms, the polyhedra of which are distorted cubes (C) and square antiprisms (A). SnTe4 and TeTe4 groups form chains along the c axis. They have a common edge and are situated in the following order T-S-T-S... . Between these chains, TlTe8 cubes and antiprisms build up columns according to the sequence A-C-A-C... . The structure of Tl2SnTe5 contains the same types of polyhedra as observed in Tl2GeTe5 but their arrangement is different. In the latter, the order is T-T-S-S... along the chains and C-C-A-A... along the columns.