SrPt3In2 – an orthorhombically distorted coloring variant of SrIn5

The new intermetallic phase SrPt3In2 was synthesized by induction-melting of the elements in a sealed tantalum ampoule followed by long-term annealing for crystal growth. The SrPt3In2 structure was refined from single crystal X-ray diffraction data: Imma, a = 1674.7(6), b = 921.2(4), c = 971.2(4) pm, wR(2) = 0.0551, 1192 F-2 values and 55 variables. Electronic structure calculations indicate strong covalent Pt-In bonding and a substantial charge transfer from the strontium atoms to the three-dimensional [Pt3In2](delta-) polyanionic network. The strontium atoms fill larger cavities within the network and the bonding of strontium to the polyanion is of the electrostatic type. The Bader charge calculations classify SrPt3In2 as a ternary platinide. The close relationship between the SrPt3In2 structure and the aristotype CaCu5 is discussed on the basis of a group-subgroup scheme in the Barnighausen formalism along with other CaCu5 coloring variants and superstructures.