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Abstract

Polycrystalline samples YbIn1-xAu1+x were prepared by reaction of the elements in sealed tantalum tubes at 1170 K with a subsequent annealing at 770 K. The crystal structures of YbInAu (space group P6;(-)2m, a = 7.6992(8), c = 4.0333(5) angstrom, wR2 = 0.035, 282 reflections and 14 variables) and YbIn0.73Au1.27 (P6;(-)2m, a = 7.706(3), c = 4.011(1) pm, wR2 = 0.035, 275 reflections, 14 parameters) were refined from single crystal X-ray diffraction data. The phase YbIn1-xAu1+x has a homogeneity range for 0.0 <= x <= 0.3 (770 K). The crystal structure of YbInAu contains two gold atoms located in tricapped trigonal prisms [Au1Yb(6)In(3)] and [Au2In(6)Yb(3)]. The indium position shows mixed occupancy by indium and gold. The main atomic interaction is the ionic one between the ytterbium (charge +1.1 is obtained from the analysis of the electron density within the quantum theory of atoms in molecules) and gold (-1.2 and -1.3) supported by the dative bonding Au -> Yb. The effective charge of indium is +0.2. Magnetic susceptibility data indicate intermediate valence for Yb increasing with increasing x. The Au-197 Mossbauer spectra show a superposition of the signals for Au1 (delta = 3.31 mm s(-1)), Au2 (delta = 5.37 mm s(-1)), and Au(In) indicating auridic character of gold.