Crystal chemistry and spectroscopic properties of ScAuSn, YAuSn, and LuAuSn

Sebastian CP, Eckert H, Rayaprol S, Hoffmann RD, Pöttgen R

Abstract

The stannides ScAuSn, YAuSn, and LuAuSn were synthesized as single phase materials from the elements via arc-melting. All samples were characterized by X-ray diffraction on powders and single crystals: MgAgAs type, F(4) over bar 3m, a = 641.94(12) pm, wR2 = 0.035, 85 F-2 values, 5 variables for ScAuSn, a = 656.52(8) pm, wR2 = 0.029, 89 F-2 values, 5 variables for LuAuSn, and NdPtSb type, P6(3)mc, a = 463.55(16), c = 737.26(15) pm, wR2 = 0.057, 233 F-2 values, 11 variables for YAuSn. The gold and tin atoms in ScAuSn and LuAuSn build up three-dimensional [AuSn] networks of corner-sharing AuSn4/4 tetrahedra (278 and 284 pm Au-Sn in ScAuSn and LuAuSn, respectively) similar to the blende type structure. The scandium atoms fill octahedral voids formed by the tin substructure. In contrast, the [AuSn] network of YAuSn is two-dimensional. The gold and tin atoms build up layers of puckered [Au3Sn3] hexagons with intralayer Au-Sn distances of 277 pm, while the interlayer Au-Sn distances of 297 pm are much longer. In every other layer the [Au3Sn3] hexagons are rotated by 60 degrees. The layers are separated by the yttrium atoms. Spectroscopic measurements indicate significant differences in the chemical bonding properties: As revealed by both Sn-119 Mossbauer spectroscopy and Sn-119 solid-state NMR data, the local electronic environment at the tin site is more anisotropic in YAuSn as compared to the other materials, which feature tin on a site with cubic point symmetry. In ScAuSn, the cubic site symmetry of the scandium position is reflected by a single sharp line in the Sc-45 solid-state NMR spectrum. (C) 2006 Elsevier SAS. All rights reserved.