DILEAD STRUCTURAL UNITS IN LEAD HALIDE AND HYDROXO/OXO MOLECULES, CLUSTERS, AND EXTENDED STRUCTURES FOUND IN MOLTEN-SALTS, AQUEOUS-SOLUTIONS, AND THE SOLID-STATE

The dilead clusters Pb2X3+ (X = F, Cl, Br, I) and Pb2(OH)22+ are stabilized by partial Pb-Pb bonding induced by bridging halide or hydroxide ions. The maximum Pb-Pb bonding (analyzed here with approximate molecular orbital calculations) is obtained in complexes with predominantly ionic lead-anion interactions. Larger lead hydroxo/oxo clusters in aqueous solution also seem to be stabilized by partial Pb-Pb bonding, but the structures of hydroxo/oxo clusters isolated in the solid state are dominated by Pb-O bonding. Only long Pb-Pb contacts are found, due to the lack of a stabilizing ionic medium. The [(PbO)2Cu]YSr2Cu2O6 family of high-T(c) superconductors contains Pb2O2 layers encapsulating a Cu(I) layer. The Pb2O2 layers are brought close enough to allow strong interlayer Pb-Pb interaction, which significantly affects the compounds' structural and electronic properties. The effects of oxidation and cation substitution on these structures are also investigated Strong analogies with the chemical bonding in dilead clusters are observed.