Formation of a water-soluble vanadium(iv) metal-polymer complex with a copolymer of vinylphosphonic acid and acrylamide: DFT quantum chemical modeling

Interactions of the citrate complexes [V^IV₂O₂(citr)₂]⁴⁻ and their protonated forms bearing polymer chains, which include vinylphosphonic acid and acrylamide units containing functional —P(O)(OH)₂ and —C(O)NH₂ groups, were studied by the DFT method at the M06/def2tzvp level of theory. The experimental IR spectra show V—O(P) stretching bands involving vanadium atoms of the coordination anion [V₂O₂(C₆H₄O₇)₂]⁴⁻ and the phosphonate oxygen atom of the copolymer —P(O)(OH)(O—)¹⁻. The formation of the V—O(P) bond between the metal complex and the phosphonate anion of the copolymer was found to be due to the presence of —CO₂H groups in the ligand environment of divanadium citrate, resulting in a decrease in the overall negative charge of the complex. Experimentally, this corresponds to the controlled protonation of the citrate ligands of the starting metal complex. In the resulting [V₂O₂(C₆H₅O₇)₂]²⁻ and [V₂O₂(C₆H₆O₇)₂]⁰ complexes, the opening of two to four chelate rings results in the formation of additional reaction sites for the binding of complexing metals to anionic phosphonate groups. The V—O(P) stretching vibrations in the calculated IR spectrum for the formation of [V₂O₂(C₆H₅O₇)₂]²⁻ are similar to the experimental values.