Synthesis and characterization of copper 4-carboxyphenylphosphonates

Abstract

Three new copper 4-carboxyphenylphosphonates with formulae Cu(HOOCC 6H 4PO 3)·2H 2O, Cu(HOOCC 6H 4PO 3) and Cu 3(OOCC 6H 4PO 3) 2·3H 2O were prepared and characterized by thermogravimetric analysis, X-ray diffraction analysis, energy-dispersive X-ray microanalysis and infrared spectroscopy. The preparation conditions of Cu(HOOCC 6H 4PO 3)·2H 2O and Cu 3(OOCC 6H 4PO 3) 2·3H 2O differ in the acidity of the reaction mixture, where Cu(HOOCC 6H 4PO 3) was prepared under hydrothermal conditions. Copper 4-carboxyphenylphosphonate with formula Cu 3(OOCC 6H 4PO 3) 2·3H 2O reacts with 4-carboxyphenylphosphonic acid to form Cu(HOOCC 6H 4PO 3)·2H 2O. Cu(HOOCC 6H 4PO 3)·2H 2O is orthorhombic, space group Pbcn (no. 60), a=8.234(2) Å, b=9.438(2) Å, c=24.899(5) Å. Cu(HOOCC 6H 4PO 3) crystallizes in the monoclinic space group P2 1/ 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 CuO 6 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(HOOCC 6H 4PO 3)·2H 2O and Cu(HOOCC 6H 4PO 3) the acid hydrogen is present at the carboxyl group and not at the phosphonic group.