Oligomeric Rare-Earth-Metal Halide Clusters. Three Structures Built of (Y16Z4)Br36 Units (Z = Ru, Ir)

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Abstract
Suitable reactions in sealed Nb tubing at 850−950 °C gave good yields of a family of oligomeric cluster phases that were characterized by single-crystal X-ray diffraction means. The basic Y16Z4 units (∼4̄ symmetry) can be derived from 2+2 condensation of centered Y6Br12Z−type clusters or as tetracapped truncated tetrahedra Y16 that are centered by a large tetrahedral Z4. These are surrounded by 36 bromine atoms which bridge edges or cap faces of the Y16Z4 nuclei and, in part, bridge to metal atoms in other clusters. The principal bonding appears to be Y−Z and Y−Br, with weaker Y−Y (d̄ ∼ 3.70 Å) and negligible Z−Z interactions. The phase Y16Br20Ru4 (P42/nnm, Z = 2; a = 11.662(1) Å, c = 16.992 (2) Å) is isostructural with Y16I20Ru4 and with the new Sc16Br20Z4 (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) Å, b = 22.361(7) Å, c = 44.702(2) Å), in which the electron-richer Ir interstitials are compensated by four additional bromine atoms and altered bridging between macroclusters. Larger amounts of YBr3 yield a third example, Y20Br36Ir4 (Y16Br24Ir4·4YBr3, I41a, Z = 4; a = 12.699(1) Å, c = 45.11(1) Å). Here infinite zigzag chains of YBr6/2 octahedra that share cis edges lie between and bridge to the Y16Ir4 clusters. All of these phases contain 60-electron, closed-shell macroclusters. Y16Br20Ru4 and Y20Br36Ir4 were found to exhibit temperature-independent (Van Vleck) paramagnetism with values typical of those found for other rare-earth-metal, zirconium, niobium, and tantalum cluster halides.