Network Formation by Condensed Tetrahedral [Au₃Al] Units in Na₂Au₃Al: Crystal and Electronic Structure, Spectroscopic Investigations, and Physical Properties of an Ordered Ternary Auride

Na₂Au₃Al, the first experimentally prepared compound in the ternary Na–Au–Al system, crystallizes in the cubic crystal system with space group P4₁32 (a = 771.42(2) pm). It can be described as a P-centered ternary ordered variant of the F-centered Laves phase MgCu₂ and is isostructural to Mo₃Al₂C. A phase width was found for the series Na₂Au_4–xAl_x allowing a successive substitution of Au by Al. The primitive structure forms for x ≥ 0.5. Na₂Au₃Al is diamagnetic at room temperature but metallic in nature, as seen from susceptibility and electrical resistivity measurements. Band structure calculations and X-ray photoelectron spectroscopy confirm the metallic nature of the title compound as states are found at the Fermi level of the DOS, along with its “auride” character. ²³Na and ²⁷Al solid-state-NMR investigations show the existence of both a disordered (x = 0.5 and 0.75) and a fully ordered (x = 1.0) representative within this series. Both COHP and Bader charge analyses suggest the presence of strong Au–Al interactions forming an anionic [Au₃Al]^δ− network, with the Na cations occupying the cavities.