TERNARY THALLIUM PLATINUM AND THALLIUM PA LLADIUM CHALCOGENIDES TL(2)M(4)X(6) - SYNTHESES, CRYSTAL-STRUCTURES, AND BONDING RELATIONS

The compounds Tl2Pt4S6, Tl2Pt4Se6, Tl2Pt4Te6 and Tl2Pd4Se6 can be synt hesized by a melting reaction from the elements or by the reaction of thallium carbonate, transition metal powder and chalcogen powder in th e temperature range between 400 degrees C and 950 degrees C. X-Ray inv estigations on single crystals and powdered samples revealed a new str ucture type for the compounds, that can be understood as stacking vari ant of the already known atom arrangement of the alkaline metal platin um chalkogenides A(2)Pt(4)X(6) (A = alkaline metal, X = S, Se). The sh ort distances thallium-platinum and thallium-palladium, respectively, as well as the results of Extended-Huckel-calculations indicate covale nt bonds between the main group and transition metal atoms.