Synthesis and characterization of copper 4-carboxyphenylphosphonates

Three new copper 4-carboxyphenylphosphonates with formulae Cu(HOOCC6H4PO3)·2H2O, Cu(HOOCC6H4PO3) and Cu3(OOCC6H4PO3)2·3H2O were prepared and characterized by thermogravimetric analysis, X-ray diffraction analysis, energy-dispersive X-ray microanalysis and infrared spectroscopy. The preparation conditions of Cu(HOOCC6H4PO3)·2H2O and Cu3(OOCC6H4PO3)2·3H2O differ in the acidity of the reaction mixture, where Cu(HOOCC6H4PO3) was prepared under hydrothermal conditions. Copper 4-carboxyphenylphosphonate with formula Cu3(OOCC6H4PO3)2·3H2O reacts with 4-carboxyphenylphosphonic acid to form Cu(HOOCC6H4PO3)·2H2O. Cu(HOOCC6H4PO3)·2H2O is orthorhombic, space group Pbcn (no. 60), a=8.234(2) Å, b=9.438(2) Å, c=24.899(5) Å. Cu(HOOCC6H4PO3) crystallizes in the monoclinic space group P21/c (no. 14), a=19.0951(3), b=8.0968(4), c=5.2111(11) Å, β=94.914(6)°, Z=4. Its layered structure is composed of distorted CuO6 octahedra arranged hexagonally in a gibbsite-like manner around two phosphonate groups, which have their carboxyphenyl groups extending into the space above and below the copper–phosphonate layer. Infrared spectra indicate that for both Cu(HOOCC6H4PO3)·2H2O and Cu(HOOCC6H4PO3) the acid hydrogen is present at the carboxyl group and not at the phosphonic group.