PREPARATION AND CRYSTAL-STRUCTURE OF SNTL4TE3 AND PBTL4TE3

We describe the synthesis and crystal structure of two ternary derivatives MTl4Te3 of the parent phase Tl5Te3. Both the derivatives, SnTl4Te3 and PbTl4Te3, crystallize with the In5Bi3 type of structure: space group I4/mcm, Z = 4. The cell constants of SnTl4Te3 (PbTl4Te3) are as follows: a = 8.819(2) angstrom (8.841(2) angstrom), c = 13.013(3) angstrom (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 additional tellurium atoms in such a way that octahedra occur, which share common vertices to build up a three dimensional infinite network infinity3[MTe6/2]. The remaining thallium atoms span cubes around the octahedra: infinity3[MTe6/2]Tl8/2 = MTl4Te3. An alternative structure description takes into account bent fragments Tl2Te with Tl-Te distances of 3.15 angstrom (3.17 angstrom) as the constitutional elements of M-centered, slightly distorted rhombic dodecahedra as the only polyhedra of the structure. Along [001] they share common vertices, whereas in the tetragonal a-a-plane they are interconnected via common faces.