Structural and electronic properties of binary and ternary platinum oxides

The structural and crystal chemistry of all known binary and ternary platinum oxides are reviewed with emphasis on the types of polyhedral linkage seen and their relationship to electronic properties. Platinum oxides generally fall into two groups: those containing divalent or partially oxidized platinum in planar coordination and those containing fully oxidized tetravalent platinum in octahedral coordination. Highly conducting platinum oxides contain columnar stacks of partially oxidized planar Pt0₄ groups with direct electronic interactions and tend towards chemical non-stoichiometry. The temperature dependence of electrical conductivity in these compounds is related to the dimensionality of the Pt-Pt interaction. Fully oxidized platinum oxides are either semiconductors or insulators, depending on the type of linkage of the octahedral coordination polyhedra and the Pt-Pt distances. The electronic configuration of octahedrally coordinated Pt⁴⁺ (low spin d⁶) precludes the possibility of metallic conductivity in these materials. In general, platinum metal is found to be fairly reactive in air at elevated temperatures, particularly in the presence of alkali and alkaline earth metals. Therefore, caution should be taken before assuming platinum containers or thermocouples are inert with respect to reactants during high temperature synthesis reactions in air or oxidizing conditions.