Transition-metal stannides with high tin content: Os4Sn17, RhSn3, RhSn4 and IrSn4

The title compounds have been prepared in well crystallized form by lengthy annealing of the elemental components with the atomic ratios varying between 1:3 and 1:10. The tin-rich matrix was dissolved in dilute hydrochloric acid. The crystal structures of these stannides were determined from single-crystal X-ray data. Os4Sn17 crystallizes with a new structure type: Pbcm, a= 694.9(1) pm, b= 1428.1 (3) pm, c= 1921.1 (4) pm, Z= 4, R= 0.023 for 1573 structure factors and 102 variables. RhSn3 is isotypic with β-CoSn3: I41/acd, a= 632.4(l) pm, c= 3412(1) pm, Z= 16, R= 0.016 for 231 F values and 21 variables. RhSn4 has a IrGe4-type structure: P312l, a= 677.4(2) pm, c= 861.4(2) pm, Z= 3 R= 0.018 (1285 F values and 26 variables). IrSn4 is isotypic with RhSn4 and IrGe4: P3121, a= 679.1(2) pm, c= 857.5(3) pm, Z= 3, K= 0.018 (1165 F values and 26 variables). In all of these structures the transition-metal (T) atoms have well defined coordination polyhedra. The coordination polyhedron of the Rh atom in RhSn3 is formed by one Rh and eight Sn atoms; in the other compounds (with higher tin content) the T atoms have (only) eight or nine Sn neighbours with T–Sn distances covering the relatively narrow range 267–303 pm. In contrast, the coordination polyhedra of the Sn atoms are difficult to define. In addition to the four (one Sn site in RhSn3) or two T neighbours (all others), each Sn atom has between ten and twelve Sn atoms in its coordination shell at distances almost continuously covering the range 286–408 pm. As a consequence the structures contain relatively large voids. Magnetic susceptibility measurements carried out with a SQUID magnetometer indicate Pauli paramagnetism for all four compounds, in agreement with the metallic conductivity found by four-probe electrical conductivity measurements for Os4Sn17, RhSn4 and IrSn4. The compounds do not become superconducting down to 2 K.