New barium 4-carboxyphenylphosphonates: Synthesis, characterization and interconversions

摘要

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 centre dot 2H_2O were prepared and characterized by elemental analysis, thermogravimetric analysis, X-ray powder diffraction, energy-dispersive X-ray microanal-ysis, 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 centre dot 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) A, beta= 127.52(1)deg, 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.