Platinum bronzes. II. Crystal structures of calcium platinum oxide (CaPt₂O₄) and cadmium platinum oxide (Cd_0.3Pt₃O₄)

The crystal structures of CaPt₂O₄ and Cd_0.3Pt₃O₄have been determined from X-ray and neutron diffraction powder data. Refinement of both X-ray and neutron intensity data led to final weighted and unweighted agreement indices of 24.6 and 16.0% for CaPt₂O₄and 6.8 and 9.8% for the simpler Cd_0.3Pt₃O₄. CaPt₂O₄has a structure that is the two-dimensional analog of the general platinum bronze structure. It crystallizes in space group D_4h ⁹-P4₂/mmc of the tetragonal system with two formula units in a cell of dimensions a = 5.7786 (5) Å and c = 5.5989 (7) Å. The structure appears to be a unique one involving nonintersecting Pt chains in the x and y directions. Pt chain compounds in one and three dimensions are known and CaPt₂O₄ forms the missing two-dimensional link. Cd_0.3Pt₃O₄ possesses the NiPt₃O₄ structure involving Pt chains in the x, y, and z directions. It crystallizes in space group Oh³-Pm3n of the cubic system with two formula units in a cell with a cell edge of 5.6423 (4) Å. The unusual formal oxidation states of Pt in both compounds are explained by extensive metallic bonding between the Pt atoms.