The Stannides AuNiSn 2 and AuCuSn 2 – Bulk Synthesis and Superstructure Determination

The stannides AuNiSn 2 and AuCuSn 2 were prepared by melting of the elements in silica ampoules at 1300 K followed by slow cooling to room temperature. The structures of both compounds were refined on the basis of single crystal X‐ray data: $P{\bar 3}m{\rm 1}$ , a = 412.41(14), c = 529.24(11) pm, wR2 = 0.0268, 159 F 2 values, 10 variables for AuNiSn 2 and a = 425.97(17), c = 526.88(15) pm, wR2 = 0.0507, 159 F 2 values, 11 variables for AuCuSn 2 (twinned crystal, BASF = 0.305(4)). These stannides crystallize with a superstructure of the NiAs type with a complete ordering of the transition metal atoms. They derive from a AuSn subcell structure, where every other layer of octahedral voids in the hexagonal closest packing of the tin atoms is filled by nickel in AuNiSn 2 and by copper in AuCuSn 2 . Due to the symmetry reduction smaller NiSn 6/6 (CuSn 6/6 ) and larger AuSn 6/6 octahedra alternate along the c axis. The crystal chemistry is discussed on the basis of a group‐subgroup scheme.