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

Na 2 Au 3 Al, the first experimentally prepared compound in the ternary Na–Au–Al system, crystallizes in the cubic crystal system with space group P 4 1 32 ( a = 771.42(2) pm). It can be described as a P -centered ternary ordered variant of the F -centered Laves phase MgCu 2 and is isostructural to Mo 3 Al 2 C. A phase width was found for the series Na 2 Au 4– x Al x allowing a successive substitution of Au by Al. The primitive structure forms for x ≥ 0.5. Na 2 Au 3 Al 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. 23 Na and 27 Al 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 [Au 3 Al] δ− network, with the Na cations occupying the cavities.