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

Abstract

NaAuAl, the first experimentally prepared compound in the ternary Na-Au-Al system, crystallizes in the cubic crystal system with space group P432 (a = 771.42(2) pm). It can be described as a P-centered ternary ordered variant of the F-centered Laves phase MgCu and is isostructural to MoAlC. A phase width was found for the series NaAuAl allowing a successive substitution of Au by Al. The primitive structure forms for x ≥ 0.5. NaAuAl 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. Na andAl 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 [AuAl] network, with the Na cations occupying the cavities.

Correlations of Crystal and Electronic Structure via NMR and X-ray Photoelectron Spectroscopies in the RETMAl2(RE = Sc, Y, La–Nd, Sm, Gd–Tm, Lu; TM = Ni, Pd, Pt) Series

“…A possible explanation for this behavior might be the fact that the MgCuAl 2 type structure features extensive Al–Al bonding, which requires a certain amount of electrons, thus lowering the electron density at the TM atoms. The binding energies determined for the RE atoms (Table ) are all slightly lower compared to the oxidic references, underlining only a certain electron transfer onto the polyanion, also in line with, for instance, the tendency observed for the Na atoms in intermetallic Na 2 Au 3 Al …”

Structural Characterization of Intermetallic Compounds by 27Al Solid State NMR Spectroscopy

“…The alkali-metal, alkaline-earth-metal, or rare-earth-metal cations are found in cavities of the polyanions. Depending on the transition metal content, the Al atoms form covalent heteroatomic bonds (e.g., Ba 3 Pt 4 Al 4 , ScPtAl and ScAuAl, or BaAuAl) or are isolated in cases of transition metal or rare-earth rich phases (RET 5 Al 2 , RE 10 TAl 3 , or Na 2 Au 3 Al). The local symmetries surrounding the Al atoms in the respective crystal structures have been depicted along with the NMR data in the following paragraphs.…”

“…For the TiNiSi, − MgZn 2 , − and LaIrSi , type compounds as well as the Heusler phases, − several papers have been published regarding the crystal chemistry, physical properties, and structural relations. The crystal chemistry of the other presented examples (Ba 3 Pt 4 Al 4 , RET 5 Al 2 , RE 10 TAl 3 , ScAuAl, and Na 2 Au 3 Al) has been discussed in great detail in the original publications. Furthermore, we would like to point out some new textbooks on intermetallics. , …”

Temperature induced valence phase transition in intermediate-valent YbPd2Al3

“…Na 2 Au 3 Al, 58 AEAuX (AE ¼ Ca-Ba, X ¼ Al-In), 59 AEAu 2 Al 2 (AE ¼ Ca, Sr) 60 2 Since the most electronegative elements acquire additional electron density, a shi towards lower binding energies can be observed in the respective XPS measurements. [58][59][60][61] Fig (green), Yb 0.33 Ca 0.67 Pd 2 Al 3 (blue), and CaPd 2 Al 3 (orange). As can be seen from the plot and the data in Table 2, only minor shi of the 3d 5/2 and 3d 3/2 lines of the Pd reference and the investigated compounds can be observed.…”