Electronic structure, physical properties and ionic mobility of LiAg2Sn

Abstract

The stannide LiAg₂Sn was synthesized from the elements by reaction in a sealed tantalum tube in a resistance furnace. LiAg₂Sn crystallizes with a ternary ordered version of the cubic BiF₃ structure, space group Fmm: a = 659.2(2) pm, wR2 = 0.0450, 69 F² values, 5 variables. The silver and tin atoms form an antifluorite structure of composition Ag₂Sn (285 pm Ag–Sn) in which the lithium atoms fill octahedral voids. Electronic structure calculations reveal weak Ag–Ag and strong Ag–Sn bonding within the Ag₂Sn substructure. LiAg₂Sn is weakly Pauli paramagnetic and a good metallic conductor. Nevertheless, the modestly small ⁷Li Knight shift is consistent with a nearly complete state of lithium ionization. The high local symmetry at the tin site is reflected by the absence of a nuclear electric quadrupolar splitting in the ¹¹⁹Sn Mössbauer spectra and a small chemical shift anisotropy evident from ¹¹⁹Sn solid state NMR. Static ⁷Li solid state NMR spectra reveals motional narrowing effects above 300 K, consistent with lithium atomic mobility on the kHz timescale.