The stannides Ca_1.692Pt₂Sn_3.308, SrPtSn₂ and EuAuSn₂

Abstract

Polycrystalline samples of the stannides Ca1.692Pt2Sn3.308, SrPtSn2 and EuAuSn2 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 Ca1.692Pt2Sn3.308 and SrPtSn2 were refined from single-crystal X-ray diffractometer data: NdRh2Sn4 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 Ca1.692(8) Pt2Sn3.308(8) and CeNiSi2 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 SrPtSn2. The calcium compound shows a homogeneity range Ca1+x Pt2Sn4−x with substantial Sn4/Ca2 mixing on one of the 4c Wyckoff positions. The [PtSn2] network is characterized by Pt–Sn (269–281 pm) and Sn–Sn (306–336 pm) bonding interactions. SrPtSn2 contains two different tin substructures: (i) Sn1–Sn1 zig-zag chains (282 pm) and (ii) orthorhombically distorted Sn2 squares (326 pm) with stronger and weaker Sn–Sn bonding. Together, the platinum and tin atoms build up a three-dimensional [PtSn2] network in which the platinum atoms have a distorted square-pyramidal tin coordination with Pt–Sn distances ranging from 261–270 pm. EuAuSn2 also crystallizes with the CeNiSi2-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) µB per Eu atom. EuAuSn2 is ordered antiferromagnetically at T N = 14.8(2) K. 151Eu 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).