THE SYNTHESIS, STRUCTURE, AND BONDING OF SC8TE3 AND Y8TE3 - COOPERATIVE MATRIX AND BONDING EFFECTS IN THE SOLID-STATE

Sc8Te3 and Y8Te3 have been prepared by high-temperature solid-state te chniques. The structures of both were determined from single-crystal a nd powder X-ray diffraction methods to be monoclinic, C2/m (No. 12) wi th Z = 8. Accurate lattice constants from Guinier powder film techniqu es at 23 degrees C for Sc8Te3 are a = 28.842(7) Angstrom, b = 3.8517(6 ) Angstrom, c = 22.352 (5) Angstrom, beta = 122.51(2)degrees; those fo r Y8Te3 are a = 31.153(7) Angstrom, b = 4.0703(4) Angstrom, c = 24.375 (5) Angstrom, beta = 122.80(2)degrees. The layered structure of the ti tle compounds consists of a complex network of chains of trans-edge-sh aring metal octahedra condensed into two types of corrugated sheets th at are separated by tellurium. In terms of metal-metal bonding (as jud ged by overlap populations), the isotypic Ti8S3 and Ti8Se3 are more 3D in aggregation, while these scandium and yttrium tellurides are 2D. T his difference in dimensionality is attributed to the cooperative effe cts of increased anion size and decreased valence electron concentrati on. This is described in detail for Sc8Te3. Contrasting paramagnetic p roperties an reported for the two, Pauli-like for Y8Te3 and temperatur e-dependent for Sc8Te3, in parallel with the behaviors of the parent m etals.