Synthesis and ab initio structure determination from powder X-ray diffraction data of a new metallic mixed-valence platinum-lead oxide PbPt2O4

The mixed-valence PbPt2O4 compound was synthesized both by solid state reaction between stoichiometric amounts of PbO and Pt heated at 650-750 degrees C for 1 week and by chemical attack of Pb2PtO4. It decomposes to PbO and Pt at 750 degrees C. The crystal structure was completely solved from direct methods and difference Fourier maps from powder X-ray diffraction data. The unit cell is triclinic (space group <P(1)over bar>, Z = 2) with a = 6.1161(2) Angstrom, b = 6.6504(2) Angstrom, c = 5.5502(2) Angstrom, alpha = 97.178(2)degrees, beta = 108.803(2)degrees, and gamma = 115.241(2)degrees. The structural model was refined using the Rietveld profile technique and led to the reliability factors R(wp) = 0.118, R(p) = 0.086, R(Bragg) = 0.029, R(F) = 0.018, and chi(2) = 1.51. The structure of PbPt2O4 appears to be a unique one involving both Pt4+ in octahedral coordination and Pt2+ or partially oxidized platinum in square-planar coordination. The PbPt2O4 structure consists of columnar-stacked PtO4 groups extending along the c axis of the unit cell. These columnar stacks are held by other planar PtO4 groups to constitute Pt3O8 sheets. These sheets are linked together by PtO6 octahedra to form a three-dimensional framework. Lead atoms are surrounded by six oxygens forming a distorted octahedron. Metallic conductivity in PbPt2O4 is consistent with short Pt-Pt bonds in the columnar stacks of PtO4 groups along the c axis direction (d(Pt-Pt) = 2.78 Angstrom). (C) 1996 Academic Press. Inc.