119 Sn Mössbauer Spectroscopy and Chemical Bonding in Au T Sn 2 ( T = Ni, Cu, Pd)

The stannides Au T Sn 2 ( 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 AuPdSn 2 was refined from single crystal diffractometer data: P 6 3 / mmc , a = 415.8(2), c = 557.1(2) pm, wR2 = 0.0400, 88 F 2 values, and 6 variable parameters. These ternary stannides derive from the NiAs structure. For AuPdSn 2 only a disordered structure with a random distribution of gold and palladium on the nickel site was observed. AuNiSn 2 and AuCuSn 2 , however, are ordered superstructures, space group $P{\bar 3}m{\rm 1}$ . 119 Sn 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 AuCuSn 2 . AuNiSn 2 , 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 AuNiSn 2 .