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

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, F4¯3m, a = 656.52(8)pm, wR2=0.035, 85 F₂ values, 5 variables for ScAuSn, a =656.52(8) pm, wR2=0.029, 89 F₂ values, 5 variables for LuAuSn, and NdPtSb type, P63mc, a =463.55(16), c=737.26(15) pm, wR2=0.057, 233 F₂ 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 AuSn 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 in ScAuSn and LuAuSn build up three-dimensional [AuSn] networks of corner-sharing AuSn_4/4 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°. The layers are separated by the yttrium atoms. Spectroscopic measurements indicate significant differences in the chemical bonding properties: As revealed by both ¹¹⁹Sn Mössbauer spectroscopy and ¹¹⁹Sn 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 ⁴⁵Sc solid-state NMR spectrum.