New barium 4-carboxyphenylphosphonates: Synthesis, characterization and interconversions

Abstract

Three new barium 4-carboxyphenylphosphonates with formulae Ba(HOOCC 6H 4PO 3H) 2, BaH(OOCC 6H 4PO 3), and Ba 3(OOCC 6H 4PO 3) 2·2H 2O were prepared and characterized by elemental analysis, thermogravimetric analysis, X-ray powder diffraction, energy-dispersive X-ray microanalysis, and infrared spectroscopy. It was found that depending on the acidity of the reaction medium, Ba(HOOCC 6H 4PO 3H) 2 can be converted to Ba 3(OOCC 6H 4PO 3) 2·2H 2O and vice versa. As an intermediate in these reactions, BaH(OOCC 6H 4PO 3) is formed. The infrared spectra of these compounds were compared with analogous strontium compounds prepared and described previously and the position of the acidic hydrogen atom in BaH(OOCC 6H 4PO 3) is deduced from the spectra. The structure of Ba(HOOCC 6H 4PO 3H) 2 was solved from X-ray powder diffraction data by an ab initio method using a FOX program with subsequent Rietveld refinement in the FullProf program. The compound is monoclinic, space group C2/ c (No. 15), a = 49.382(1), b = 5.5196(1), c = 8.4977(2) Å, β = 127.52(1)°, and Z = 4. This compound has a layered structure built up from CPO 3 phosphonate tetrahedra and BaO 8 distorted tetragonal antiprisms and thus forming layers in the bc plane with organic groups pointing to the interlayer space.