Synthesis and crystal structure of Zr2Te.: Distinctions in bonding to isotypic Sc2Te and the relationship to the structures of congeneric Hf2Te and Zr2Se

Zr2Te is accessible by high-temperature synthesis. The structure of the zirconium-rich telluride was determined by means of powder X-ray diffraction to be orthorhombic, Pnma (No. 62), Z = 12, Pearson symbol oP36, a = 1995.0(2) pm, b = 382.36(2) pm, c = 1065.63(9) pm. Pairwise interpenetrating columns of trans-face-shared, centered Zr-9 cuboids, reminiscent of the bcc high-temperature form of zirconium can be recognized as the topologically characteristic structural feature. Tellurium atoms capping the remaining square faces complete the motif of a (1)(infinity)[Zr8Te4] double string running parallel [010]. The tellurium atoms are 7-, 8- and 9-fold coordinated by zirconium. The coordination figures represent mono-, bi- and tricapped distorted trigonal prisms, with zirconium atoms capping the square faces of the prisms. Extended Huckel calculations revealed distinctions in bonding in Zr2Te and the isotypic Sc2Te. According to Mulliken overlap populations, the heteronuclear interactions are similar in both tellurides. However, the lower valence electron concentration available for M-M bonding in Sc2Te is reflected in a considerable restriction of the attractive homonuclear interactions to one-dimensional metal cores, whereas in Zr2Te M-M bonding regions extend in space. The structure of Zr2Te is contrasted with two other types of bcc fragment structures adopted by the congeneric Hf2Te and Zr2Se. We show that the structural diversity observed for various dimetal chalcogenides is controlled by an intimate interplay of electronic and geometric factors.