Gold-Tin Ordering in SrAu<sub>2</sub>Sn<sub>2</sub>

Samples of the solid solutions SrAu_xSn_4−x (1.7 ≤ x ≤ 2.2) were obtained by high-frequency melting of the elements in sealed niobium ampoules. Powder and single-crystal X-ray data confirmed the CaBe₂Ge₂-type structure, space group P4/nmm. The structures of SrAu_1.76Sn_2.24, SrAu₂Sn₂, SrAu_2.16Sn_1.84 (crystal A), SrAu_2.16Sn_1.84 (crystal B), and SrAu_2.22Sn_1.78 were refined from single-crystal diffractometer data. Only the SrAu₂Sn₂ crystal shows complete Au-Sn ordering while all other crystals show substantial mixed occupancies on the four crystallographically independent sites of the polyanionic networks in which the strontium atoms fill cages of coordination number 16. Temperature-dependent susceptibility measurements have revealed diamagnetism for SrAu₂Sn₂. ¹¹⁹Sn Mössbauer spectroscopic data of a bulk SrAu₂Sn₂ sample have resolved the tetrahedral and square-pyramidal tin sites but point to substantial Au-Sn disorder.