NEW CHALCOGENOMETALLATES OF IVA AND VA METALS WITH LAYERED COMPLEX ANIONS Kurt O. Klepp, Doris Gurtner and Dietmar Sturmayr, Dept. of Inorg. Chemistry, Kepler University, Altenbergerstr. 69, A-4040 Linz, Austria.

An investigation of the sections Tl_3-X M_XT^VX₄ (M = Cu,Ag; T=V,Nb,Ta,

X = S,Se) led ,among others [1], to the pseudo two-dimensional compounds Tl₂Cu₄T₂S₈ and Tl₄Ag₂Ta₂S₈. In the former CuS₄ and TS₄ tetrahedra share edges to form corrugated layers which can be interpreted as fragments of the sulvanite type structure. Tetrahedral coordination of the transition metals is also found in Tl₄Ag₂Ta₂S₈. Almost planar layers, built up by double tetrahedra [S₂AgS₂TaS₂] sharing their free corners, run through the structure parallel to (101).

The complex anions in the isostructural series Tl₂Cu₂T^IV₃X₈ consist of corrugated layers which are built up by edge and corner sharing T^IVX₆ octahedra which run parallel to (201). Corrugation of these layers leads to the formation of distorted tetrahedral niches which are occupied by Cu. The Tl⁺-ions between the layers are in a bicapped trigonal prismatic chalcogen coordination. Homologous layers are found in Rb₂Cu₂Hf₃Se₈, however here their stacking leads to two entirely different chalcogen coordinations for the two independent Rb⁺ ions; one of them occupies a split position and shows drastically enhanced thermal displacements.

[1] K.O. Klepp, D. Mayr & H. Boller, IV ^th European Conference on Solid State Chemistry, Dresden 1992,Book of Abstracts, p.363.