Synthesis and crystal structures of four pH-dependent Pb(II) and Cd(II) phosphonates based on a novel ligand, 3-phosphono-benzoic acid

Four metal phosphonate hybrid compounds, [Pb(Hpbc)] (1), [Pb3(pbc)2(H2O)2] (2), [Cd(H2pbc)2(H2O)2] (3) and [Cd1.5(pbc)(H2O)1.5] · 0.5H2O (4) (H3pbc = 3-phosphono-benzoic acid) were successfully synthesized by the hydrothermal/solvothermal reaction of metal acetate and 3-phosphono-benzoic acid. Compounds 1–4 were pH-dependent products and characterized by elemental analysis, Fourier transform infrared (FT-IR) spectra and single-crystal X-ray diffraction studies. Compound 1 is a two-dimensional (2D) structure constructed by inorganic layer and organic pendant. With the increase of pH value, structure 2 shows 3D inorganic framework with distributing organic moieties in the channels. In 3, the Cd2O10 dimers are linked by alternating terminal and bridging ligands, resulting in 1D chain structure. Compound 4 is a 2D structure where the 1D inorganic chains are connected by the organic moieties of the ligands.