PREPARATION AND CRYSTAL-STRUCTURE OF SNTL4TE3 AND PBTL4TE3

We describe the synthesis and crystal structure of two ternary derivat ives MTl4Te3 of the parent phase Tl5Te3. Both the derivatives, SnTl4Te 3 and PbTl4Te3, crystallize with the In5Bi3 type of structure: space g roup I4/mcm, Z = 4. The cell constants of SnTl4Te3 (PbTl4Te3) are as f ollows: a = 8.819(2) angstrom (8.841(2) angstrom), c = 13.013(3) angst rom (13.056(3) angstrom), c/a = 1.47 (1.48). Short M-Te distances of 3 .25 angstrom (3.26 angstrom) are obtained in infinity1[MTe2/2] chains, which run along [001]. The M atoms are further surrounded by addition al tellurium atoms in such a way that octahedra occur, which share com mon vertices to build up a three dimensional infinite network infinity 3[MTe6/2]. The remaining thallium atoms span cubes around the octahedr a: infinity3[MTe6/2]Tl8/2 = MTl4Te3. An alternative structure descript ion takes into account bent fragments Tl2Te with Tl-Te distances of 3. 15 angstrom (3.17 angstrom) as the constitutional elements of M-center ed, slightly distorted rhombic dodecahedra as the only polyhedra of th e structure. Along [001] they share common vertices, whereas in the te tragonal a-a-plane they are interconnected via common faces.