¹¹⁹Sn Mössbauer spectroscopy and chemical bonding in AuTSn₂ (T = Ni, Cu, Pd)

The stannides AuTSn₂ (T = Ni, Cu, Pd) were synthesized by reacting the elements in sealed silica ampoules at 1300 K and subsequent annealing sequences. The compounds were studied by X-ray powder diffraction. The structure of the new stannide AuPdSn₂ was refined from single crystal diffractometer data: P6₃/ mmc, a = 415.8(2), c = 557.1(2) pm, wR2 = 0.0400, 88 F² values, and 6 variable parameters. These ternary stannides derive from the NiAs structure. For AuPdSn₂ only a disordered structure with a random distribution of gold and palladium on the nickel site was observed. AuNiSn₂ and AuCuSn₂, however, are ordered superstructures, space group P3m1. ¹¹⁹Sn Mössbauer spectra show single signals at isomer shifts of 2.00(1) (Ni), 2.10(1) (Pd), and 2.26(1) mm/s (Cu), indicating the highest s electron density at the tin nuclei of AuCuSn₂. AuNiSn₂, where the tin atoms show the strongest displacement from the subcell mirror plane reveals the largest quadrupole splitting of 0.60(1) mm/s. Chemical bonding in AuSn and AuNiSn ₂ was compared on the basis of TB-LMTO-ASA electronic structure calculations. The latter reveal strong Au-Ni and Ni-Sn bonding in the ordered structure of AuNiSn₂.