The stannides Ca${}_{1.692}$Pt${}_2$Sn${}_{3.308}$, SrPtSn${}_2$ and EuAuSn${}_2$

Polycrystalline samples of the stannides Ca${}_{1.692}$Pt${}_2$Sn${}_{3.308}$, SrPtSn${}_2$ and EuAuSn${}_2$ were synthesized directly from the elements, using sealed tantalum ampoules as crucible material. The reactions were performed in muffle or induction furnaces. The phase purity of the samples was studied by X-ray powder diffraction (Guinier technique). The structures of Ca${}_{1.692}$Pt${}_2$Sn${}_{3.308}$ and SrPtSn${}_2$ were refined from single-crystal X-ray diffractometer data: NdRh${}_2$Sn${}_4$ type, Pnma, a = 1887.22(13), b = 441.22(3), c = 742.89(4) pm, wR = 0.0626, 1325 F${}^2$ values, 45 variables for Ca${}_{1.692\left(8\right)}$ Pt${}_2$Sn${}_{3.308\left(8\right)}$ and CeNiSi${}_2$ type, Cmcm, a = 462.59(5), b = 1932.8(2), c = 458.00(5) pm, wR = 0.0549, 481 F${}^2$ values, 18 variables for SrPtSn${}_2$. The calcium compound shows a homogeneity range Ca${}_{1+x}$Pt${}_2$Sn${}_{4-x}$ with substantial Sn${}_4$/Ca${}_2$ mixing on one of the 4c Wyckoff positions. The [PtSn${}_2$] network is characterized by Pt–Sn (269–281 pm) and Sn–Sn (306–336 pm) bonding interactions. SrPtSn${}_2$ contains two different tin substructures: (i) Sn1–Sn1 zig-zag chains (282 pm) and (ii) orthorhombically distorted Sn${}_2$ squares (326 pm) with stronger and weaker Sn–Sn bonding. Together, the platinum and tin atoms build up a three-dimensional [PtSn${}_2$] network in which the platinum atoms have a distorted square-pyramidal tin coordination with Pt–Sn distances ranging from 261–270 pm. EuAuSn${}_2$ also crystallizes with the CeNiSi${}_2$-type structure with the lattice parameters a = 453.9(1), b = 2018.9(5) and c = 456.8(1) pm. Temperature dependent magnetic susceptibility studies indicate europium(II) with an experimental magnetic moment of 8.28(2) µ${}_B$ per Eu atom. EuAuSn${}_2$ is ordered antiferromagnetically at T${}_N$ = 14.8(2) K. ${}^{151}$Eu Mössbauer spectra confirm the oxidation state +2 for europium (isomer shift δ = -11.17(2) mm s${}^{-1}$) and the magnetic ordering at low temperature (21.8 T magnetic hyperfine field at 6 K).