title: Structure and lithium dynamics of Li2AuSn2--a ternary stannide with condensed AuSn4/2 tetrahedra.
abstract: The new stannide Li(2)AuSn(2) was prepared by reaction of the elements in a sealed tantalum tube in a resistance furnace at 970 K followed by annealing at 720 K for five days. Li(2)AuSn(2) was investigated by X-ray diffraction on powders and single crystals and the structure was refined from single-crystal data: Z=4, I4(1)/amd, a=455.60(7), c=1957.4(4) pm, wR2=0.0681, 278 F(2) values, 10 parameters. The gold atoms display a slightly distorted tetrahedral tin coordination with Au-Sn distances of 273 pm. These tetrahedra are condensed through common corners leading to the formation of two-dimensional AuSn(4/2) layers. The latter are connected in the third dimension through Sn-Sn bonds (296 pm). The lithium atoms fill distorted hexagonal channels formed by the three-dimensional [AuSn(2)] network. Modestly small (7)Li Knight shifts are measured by solid-state NMR spectroscopy that are consistent with a nearly complete state of lithium ionization. The noncubic local symmetry at the tin site is reflected by a nuclear electric quadrupolar splitting in the (119)Sn Mössbauer spectra and a small chemical shift anisotropy evident from (119)Sn solid-state NMR spectroscopy. Variable-temperature static (7)Li solid-state NMR spectra reveal motional narrowing effects at temperatures above 200 K, revealing lithium atomic mobility on the kHz time scale. Detailed lineshape as well as temperature-dependent spin lattice relaxation time measurements indicate an activation energy of lithium motion of 27 kJ mol(-1).
authors.affiliation: Institut für Physikalische Chemie und Sonderforschungsbereich 458, Universität Münster, Schlossplatz 4/7, 48149 Münster, Germany.
authors.forename: Zhiyun
authors.initials: Z
authors.lastname: Wu
authors.forename: Bernd D
authors.initials: BD
authors.lastname: Mosel
authors.forename: Hellmut
authors.initials: H
authors.lastname: Eckert
authors.forename: Rolf-Dieter
authors.initials: RD
authors.lastname: Hoffmann
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen
mesh_terms: D000497:Alloys / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D008094:Lithium / Q000737:chemistry*; D008958:Models, Molecular; D014001:Tin / Q000737:chemistry*
chemical_list: D000497:Alloys; D014001:Tin; D006046:Gold; D008094:Lithium