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

Abstract

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 Na2Au4-xAlx 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.