OLIGOMERIC RARE-EARTH-METAL HALIDE CLUSTERS - 3 STRUCTURES BUILT OF (Y(16)Z(4))BR-36 UNITS (Z=RU,IR)

Suitable reactions in sealed Nb tubing at 850-950 degrees C gave good yields of a family of oligomeric cluster phases that were characterize d by single-crystal X-ray diffraction means. The basic Y(16)Z(4) units (similar to (4) over bar symmetry) can be derived from 2+2 condensati on of centered Y(6)Br(12)Z-type clusters or as tetracapped truncated t etrahedra Y-16 that are centered by a large tetrahedral Z(4). These ar e surrounded by 36 bromine atoms which bridge edges or cap faces of th e Y(16)Z(4) nuclei and, in part, bridge to metal atoms in other cluste rs. The principal bonding appears to be Y-Z and Y-Br, with weaker Y-Y (d similar to 3.70 Angstrom) and negligible Z-Z interactions. The phas e Y16Br20Ru4 (P4(2)/nnm, Z = 2; a = 11.662(1) Angstrom, c = 16.992 (2) Angstrom) is isostructural with Y16I20Ru4 and with the new Sc(16)Br(2 0)Z(4) (Z = Fe, Os). Syntheses only in the presence of Ir and ABr-YBr3 fluxes (A = K-Cs) produce Y16Br24Ir4 (Fddd, Z = 8; a = 11.718(3) Angs trom, b = 22.361(7) Angstrom, c = 44.702(2) Angstrom), in which the el ectron-richer Ir interstitials are compensated by four additional brom ine atoms and altered bridging between macroclusters. Larger amounts o f YBr3 yield a third example, Y30Br36-Ir-4(Y(16)Br(24)Tr(4) . 4YBr(3), I4(1)a, Z = 4; a = 12.699(1) Angstrom, c = 45.11--(I) (1) Angstrom). Here infinite zigzag chains of YBr6/2 octahedra that share cis edges l ie between and bridge to the Y16Ir4 clusters. All of these phases cont ain 60-electron, closed-shell macroclusters. Y16Br20Ru4 and Y20Br36Ir4 were found to exhibit temperature-independent (Van Vleck) paramagneti sm with values typical of those found for other rare-earth-metal, zirc onium, niobium, and tantalum cluster halides.