AUTA5S - A CUBIC ROD PACKING OF CONDENSED (AU,TA)(13) ICOSAHEDRA INTERWOVEN WITH A 3-DIMENSIONAL FRAMEWORK OF CORNER-CONNECTED STA6 OCTAHEDRA

AuTa5S was prepared from a compressed mixture of tantalum disulfide, t antalum, and gold in a sealed tantalum capsule at 1650 K within 2 days , Above 1750 K the sulfide disproportionates in the solid state. The s tructure of AuTa5S (a = 1250.82(3) pm, F (4) over bar 3m, Z = 16, Pear son symbol cF112) was determined from integrated X-ray powder diffract ion intensities by direct methods and subsequently refined by fitting the profiles (13 structure variables, R-wp = 0.036), Three of five cry stallographically distinct metal atoms have distorted icosahedral coor dinations, Sulfur is trigonal antiprismatically coordinated by tantalu m, The structure is composed of two mutually interpenetrating zinc ble nde-like frameworks consisting of corner-connected STa6 octahedra and corner-connected Au4Ta4 and Ta4Ta4 stellae quadrangulae. The unique st ructure of AuTa5S represents a link between two major intermetallic st ructure families, the eta-carbide-type and the Mn23Th6-type structures . (C) 1998 Academic Press.