Synthesis, crystal structures, and surface photovoltage properties of four new metal diphosphonates based on the mixed ligands

Abstract

By introduction of 2,2′-bipy or 1,10-phen as a second organic ligand, four new metal diphosphonates with mixed ligands, namely, [M(2,2′-bipy)(hedpH₃)₂]·H₂O (M = Co (1), Ni (2)), [M(1,10-phen)(hedpH₃)₂]·H₂O (M = Co (3), Ni (4)) (hedpH₄ = 1-hydroxyethylidenediphosphonic acid, 2,2′-bipy = 2,2′-bipyridine, 1,10-phen = 1,10-phenanthroline), have been synthesized under hydrothermal conditions. Compounds 1 and 2 are isostructural and adopt a 2D supramolecular network. Each {MN₂O₄} octahedron and four {CPO₃} tetrahedra are interconnected into a {M(2,2′-bipy)(hedpH₃)₂} (M = Co (1), Ni (2)) unit via corner-sharing. These isolated units are interlinked through hydrogen bonding interactions to form 1D infinite chains, which are further assembled into a 2D supramolecular network through π–π stacking interactions. Compounds 3 and 4 are also isostructural and show a 1D double chain structure constructed from {M(1,10-phen)(hedpH₃)₂} (M = Co (3), Ni (4)) units. In compounds 3 and 4, the {M(1,10-phen)(hedpH₃)₂} units are linked to each other through hydrogen bonds to form a 1D infinite chain and then these 1D chains are further extended into 1D double chains by π–π stacking interactions. The surface photovoltage properties of compounds 1–4 have been investigated.