The stability constants of cadmium(II) complexes with the glycylglycinate anion in aqueous dimethyl sulfoxide (DMSO) solutions were determined by potentiometric titration at 298 K and an ionic strength of 0.1 M. An increase in DMSO concentration in the solution leads to higher stability of cadmium(II) glycylglycinate complexes. Using both experimental and literature data, the Gibbs transfer energies of cadmium(II) glycylglycinate complexes from water to aqueous–DMSO solvent mixtures were calculated, and the contribution of reagent resolution to the change in Gibbs energy of the complex formation reaction was analyzed. It was shown that the enhanced stability of cadmium(II) glycylglycinate complexes in aqueous DMSO solutions is mainly due to weakened solvation of the ligand.
V.A. Isaeva (Wed,) studied this question.