Effect of the Composition of a Water–Dimethyl Sulfoxide Solvent on the Stability of Nickel(II)–Cryptand[2.2.2] Complexes

Constants of stability of nickel(II)–cryptand[2.2.2] complexes in aqueous dimethyl sulfoxide solutions with variable contents of the organic cosolvent are determined via potentiometric titration at T = 298 K. It is found that the stability of mononuclear nickel(II) cryptate falls as that of the binuclear complex rises along with the concentration of dimethyl sulfoxide in a solution. An increase in the stability of protonated nickel(II) cryptate is also observed in the region of high dimethyl sulfoxide concentrations. The Gibbs energies of transferring nickel(II) ions from water to a water–dimethyl sulfoxide solvent are calculated using literature data. The contributions from the resolvation of the reactants in water–dimethyl sulfoxide mixtures to the change in the stability of nickel(II)–cryptand[2.2.2] complexes are determined.