The stannides SrPdSn and m-BaPtSn

The stannides SrPdSn (TiNiSi type, orthorhombic space group Pnma) and m-BaPtSn (EuNiGe type, monoclinic space group P2${}_1$/c) were synthesized from the elements in sealed tantalum ampoules in a high-frequency furnace. Their structures were refined from single-crystal X-ray diffraction data. SrPdSn crystallizes directly from the melt and is stable upon annealing at T = 1073 K. A BaPtSn sample quenched from the melt adopts the cubic LaIrSi-type structure, cubic space group P2${}_1$3 (c-BaPtSn) and shows a temperature induced (annealing at 1070 K) structural phase transition leading to a EuNiGe-type low-temperature modification m-BaPtSn. The phase transition leads to a reconstruction within the polyanionic [PtSn]${}^{\delta -}$ network. The latter is three-dimensional and composed of ten-membered Pt${}_5$Sn${}_5$ rings in c-BaPtSn, while the polyanion is two-dimensional in m-BaPtSn and is composed of condensed Pt${}_4$Sn${}_4$ and Pt${}_2$Sn${}_2$ rings. The two-dimensional substructure leads to a strong moisture sensitivity for m-BaPtSn. The Pt-Sn distances in both modifications range from 257 to 267 pm, indicating substantial covalent bonding.