Ternary arsenides based on platinum-indium and palladium-indium fragments of the Cu3Au-type: Crystal structures and chemical bonding

Three metal-rich palladium-indium and platinum-indium arsenides, Pd5InAs, Pt5InAs, and Pt8In2As, were synthesized using a high-temperature ampoule technique. Their crystal structures were determined from Rietveld analysis of powder diffraction data. All the compounds crystallize in tetragonal system with P4/mmm space group (Pd5InAs: a = 3.9874(1) Å, c = 6.9848(2) Å, Z = 1, Rp = 0.053; Rb = 0.013; Pt5InAs: a = 3.9981(2) Å, c = 7.0597(4) Å, Z = 1, Rp = 0.058, Rb = 0.016; Pt8In2As: a = 3.9872(3) Å, c = 11.1129(7) Å, Z = 1, Rp = 0.047; Rb = 0.014). The first two compounds belong to the Pd5TlAs structure type, while the third one is isotypic with the recently discovered Pd8In2Se. Main structural units in all arsenides are indium-centered [TM12In] cuboctahedra (TM = Pd, Pt) of the Cu3Au type, single- and double-stacked along the c axis in TM5InAs and Pt8In2As, respectively, alternating with [TM8As] rectangular prisms. DFT electronic structure calculations predict all three compounds to be 3D metallic conductors and Pauli-like paramagnets. According to the bonding analysis based on the electron localization function and electron localizability indicator topologies, all compounds feature multi-centered interactions between transition metal and indium in their heterometallic fragments. Additionally, pairwise interactions between platinum atoms are also observed, indicating a somewhat more localized bonding in the case of platinum-based compounds.