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

The previously reported high-pressure compound Os3Sn7 was prepared at normal pressure by long-time annealing of the elemental components at 300 degrees C. Its Ir3Ge7-type crystal structure was refined from single-crystal X-ray data: Im (3) over bar m, a=937.8(2) pm, R=0.037 for 220 F values and 11 variable parameters. The structure of Ir5Sn7 and that of the low-temperature (alpha) modification of PdSn2 are confirmed and refined from single-crystal data. Ir5Sn7 has the tetragonal Co5Ge7 type structure: I4mm, a=X53.6(1) pm, c=646.5(1) pm, R=0.026, 828 F values, 23 parameters; alpha-PdSn2 (own type): I4(1/)acd, a=649.0(1) pm, c=2432.7(5) pm, R=0.026, 250 F values, 17 variables. The structure of PtSn4, previously described with the non-centrosymmetric space group Aba2, could be refined in the centrosymmetric group Ccca: a=641.8(3) pm, b=1136.6(6) pm, c=638.4(2) pm, R=0.025 for 436 F valves and 14 variables. The isotypic palladium compound forms a solid solution with nickel, where the structure was refined for a single-crystal of the composition Ni0.402(4)Pd0.598Sn4 to R=0.020. Ir5Sn7, alpha-PdSn2 and PtSn4 are diamagnetic at room temperature and show metallic conductivity. The structures of CoSn2. alpha-PdSn2, PtSn2 and PtSn4 are closely related and may be described as stacking variants of each other. (C) 2000 Elsevier Science S.A. All rights reserved.