A new series of mixed oxalates MM'(C_2O_4)_3(H_2O)_3 centre dot nH_2O (M = Cd, Hg, Pb; M' = Zr, Hf) based on eight-fold coordinated Metals: Synthesis, crystal structure from single-crystal and powder diffraction data and thermal behaviour

摘要

A new series of mixed oxalates MM'(C_2O_4)_3(H_2O)_3 centre dot nH_2O (M = Cd, Hg, Pb; M' = Zr, Hf) has been prepared. The crystal structures have been solved from single-crystal and powder diffraction data. The isotypical compounds crystallise with space group P2_1/c (No. 14). The structures consist of honeycomb layers formed by eight-fold coordinated metals, in a distorted square-based antiprismatic conformation, connected together via oxalates which act as bidentate ligands and also as monodentate in a less-common mu 3-bridging mode. Sheets are built from two shifted honeycomb layers and linked to each other through a hydrogen network. The resulting frameworks of the series display a compact two-dimensional arrangement of polyhedra MO_8 and M'O_8. Weakly-bonded water molecules are located between and within the sheets. Comparisons with the 3D open-framework structures of related metal oxalates are made. The dehydration processes occur in three or four steps. The final products are MO, M'O_2 and PbZrO_3 resulting from the sublimation of PbO in air. The size of PbZrO_3 crystallites, which are on average isotropic, has been evaluated to be 1055 A from line-broadening analysis.