Synthesis, structures and surface photovoltage properties of four novel metal phosphonates with a 3D supramolecular structure

By introduction of oxalate as a second organic ligand, four novel metal phosphonates with a 3D supramolecular structure, namely, M-1.5(H2O)[(H2L)(C2O4)(0.5)] (M = Fe (1), Co (2), Zn (3)) and Cu-1.5[(H2L)(C2O4)(0.5)] (4) (H4L = C5H4NCH2CH(OH)(PO3H2)(2)), have been synthesized under hydrothermal conditions. Compounds 1-3 are isostructural and adopt a three-dimensional supramolecular structure. Every two {M(1)O-5} polyhedra are interconnected by {CPO3} tetrahedra to form a unit and these units are linked by {M(2)O-6} octahedra to form a 1D chain by corner-sharing down the c-axis. Such 1D infinite chains are cross-linked via oxalate anions into a 2D layer, which are further connected through hydrogen bonding interactions to give rise to a 3D supramolecular structure. The overall structure of compound 4 is similar to that of compounds 1-3 except that the {M(2)O-6} octahedra are replaced by {Cu(2)O-4} planar squares. Surface photovoltage properties of the four compounds have also been studied.