On Ternary Intermetallic Aurides: CaAu2Al2, SrAu2- xAl2+ x and Ba3Au5+ xAl6- x.

The intermetallic compound CaAu₂Al₂, and the members of the solid solutions SrAu_{2- x}Al_{2+ x} (0 ≤ x ≤ 0.33) and Ba₃Au_{5+ x}Al_{6- x} ( x = 0, 0.14, 0.49) were synthesized from the elements in sealed tantalum ampoules. The Ca compound crystallizes with the orthorhombic ThRu₂P₂ type structure, whereas the targeted SrAu₂Al₂ was found to form a solid solution according to SrAu_{2- x}Al_{2+ x}. For the Ba system no 'BaAu₂Al₂' was found, however, Ba₃Au_{5+ x}Al_{6- x} was discovered to crystallize in the monoclinic space group C2/ c with its own structure type. The samples were investigated by powder X-ray diffraction and their crystal structures were refined on the basis of single-crystal X-ray diffraction data. All compounds were characterized furthermore by susceptibility measurements. The crystallographic aluminum sites of CaAu₂Al₂ and Ba₃Au₅Al₆ can be differentiated by ²⁷Al solid state NMR spectra on the basis of their different electric field gradients, in agreement with theoretical calculations. The electron transfer from the alkaline earth metals and the aluminum atoms onto the gold atoms was investigated by X-ray photoelectron spectroscopy (XPS) classifying these intermetallics as aurides, in full agreement with the calculated Bader charges. [ABSTRACT FROM AUTHOR]