Structure refinements and some properties of the transition metal stannides Os3Sn7, Ir5Sn7, Ni0.402(4)Pd0.598Sn4, alpha-PdSn2 and PtSn4

The previously reported high-pressure compound Os3Sn7 was prepared at norma l pressure by long-time annealing of the elemental components at 300 degree s C. Its Ir3Ge7-type crystal structure was refined from single-crystal X-ra y data: Im (3) over bar m, a=937.8(2) pm, R=0.037 for 220 F values and 11 v ariable parameters. The structure of Ir5Sn7 and that of the low-temperature (alpha) modification of PdSn2 are confirmed and refined from single-crysta l data. Ir5Sn7 has the tetragonal Co5Ge7 type structure: I4mm, a=X53.6(1) p m, c=646.5(1) pm, R=0.026, 828 F values, 23 parameters; alpha-PdSn2 (own ty pe): I4(1/)acd, a=649.0(1) pm, c=2432.7(5) pm, R=0.026, 250 F values, 17 va riables. The structure of PtSn4, previously described with the non-centrosy mmetric space group Aba2, could be refined in the centrosymmetric group Ccc a: a=641.8(3) pm, b=1136.6(6) pm, c=638.4(2) pm, R=0.025 for 436 F valves a nd 14 variables. The isotypic palladium compound forms a solid solution wit h nickel, where the structure was refined for a single-crystal of the compo sition Ni0.402(4)Pd0.598Sn4 to R=0.020. Ir5Sn7, alpha-PdSn2 and PtSn4 are d iamagnetic at room temperature and show metallic conductivity. The structur es of CoSn2. alpha-PdSn2, PtSn2 and PtSn4 are closely related and may be de scribed as stacking variants of each other. (C) 2000 Elsevier Science S.A. All rights reserved.