31P NMR study of the stoichiometry, stability and thermodynamics of new complexation between uranyl (II) nitrate and N-methyliminobis(methylenephosphonic acid) in two binary D2O-DMSO-d6 solvent mixtures

The complexation reaction between uranyl (II) nitrate, and N-methyliminobis(methylenephosphonic acid) (MIDPH) was investigated in two different binary solvent mixtures of D2O-DMSO-d(6) at various temperatures using P-31 NMR spectroscopy. The exchange between the free ligand and the 1:1 complexed ligand was slow on the NMR timescale and two P-31 NMR signals were observed. The formation constant of the resulting complex was evaluated from integration of the two P-31 NMR signals. The values of thermodynamic parameters of the resulting complex (Delta H, Delta S and Delta G) were determined from the temperature dependence of the formation constants. In the two solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. Published by Elsevier Ltd.