Transition metal-tin ordering in SrPtSn, SrAuSn and BaAuSn and 119Sn Mossbauer spectroscopy of CaPdSn, CaPtSn and SrAuSn

Pure samples of CaPdSn, CaPtSn, SrPtSn, SrAuSn and BaAuSn can be prepared by reacting the elements in glassy carbon crucibles or in sealed tantalum tubes in a water-cooled sample chamber of a high-frequency furnace. The stannides have been investigated by X-ray diffraction on powders. Single crystal data yielded: TiNiSi type, Pnma, a = 764.16(7) b = 470.74(4), c = 799.64(7) pm, wR(2) = 0.0622, 469 F-2 values, 20 variables for SrPtSn, and CaCuGe type, Pnma, a = 2341.4(3), b = 481.80(5), c = 826.7(1) pm, wR(2) = 0. 1368, 1136 F-2 values, 56 variables for SrAuSn. The platinum (gold) and tin atoms form two-dimensional layers of puckered Pt3Sn3 and Au3Sn3 hexagons with short Pt-Sn (276 and 278 pm) and Au-Sn (279-286 pm) intralayer distances. These condensed two-dimensionally infinite nets are interconnected to each other via Pt-Sn contacts (279 pm) in SrPtSn. In SrAuSn very weak interlayer Au-Sn (312 pm) and Au-Au (340 pm) contacts occur, but stronger Sn-Sn (304 pm) interactions. The SrAuSn structure is a superstructure of SrPtSn resulting from an isomorphic transition of index 3 from Pnma to Pnma. The KHg2 type subcell of BaAuSn was determined from Guinier powder data: Imma, a = 493.5(1), b = 817.2(1), c = 844.5(1) pm. Sn-119 Mossbauer spectra of TiNiSi type CaPdSn and CaPtSn show a single signal at 77 K at isomer shifts of delta = 1.964(5) and 1.857(4) mm s(-1), respectively, subject to quadrupole splitting of DeltaE(Q) = 0.94(3) and 0.89(1) mm s(-1). SrAuSn shows two superimposed signals in a ratio of 2 : 1 at 77 K : delta(1) = 2.03(5), delta(2) = 2.12(5) mm s(-1), DeltaE(Q1) = 0.9(1) and DeltaE(Q2) = 0.6(2) mm s(-1). (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.