Equiatomic AEAuX (AE = Ca-Ba, X = Al-In) Intermetallics: A Systematic Study of their Electronic Structure and Spectroscopic Properties

The three intermetallic compounds SrAuGa, BaAuAl and BaAuGa were synthesised from the elements in niobium ampoules. The Sr compound crystallises in the orthorhombic KHg2-type structure (Imma, a=465.6(1), b=771.8(2), c=792.6(2) pm, wR(2)=0.0740, 324 F-2 values, 13 variables), whereas the Ba compounds were both found to crystallise in the cubic non-centrosymmetric LaIrSi-type structure (P2(1)3, BaAuAl: a=696.5(1) pm; wR(2)=0.0427, 446 F-2 values, 12 variables; BaAuGa: a=693.49(4) pm, wR(2)=0.0717, 447 F-2 values, 12 variables). The samples were investigated by powder X-ray diffraction and their structures refined on the basis of single-crystal X-ray diffraction data. The title compounds, along with references from the literature (CaAuAl, CaAuGa, CaAuIn, and SrAuIn), were characterised further by susceptibility measurements and Al-27 and Ga-71 solid-state NMR spectroscopy. Theoretical calculations of the density of states (DOS) and the NMR parameters were used for the interpretation of the spectroscopic data. The electron transfer from the alkaline-earth metals and the group 13 elements onto the gold atoms was investigated through X-ray photoelectron spectroscopy (XPS), classifying these intermetallics as aurides