Complexation of Silver(I) with 1-Methyl-2-mercaptoimidazole in the Aqueous Dimethylsulfoxide Solvent

The paper presents the thermodynamic parameters of acid–base equilibria of 1-methyl-2-mercaptoimidazole (1MI) and its complexation with the silver(I) ion in aqueous dimethylsulfoxide. An analysis of the solvation contributions of reagents to the change in the Gibbs energy of protonation of 1MI showed that the practically zero changes in the Gibbs energy of the transfer of the reaction from water to a solvent with a composition of 0.1 mole fractions DMSO are due to complete compensation of the solvation contribution of the protonated 1-methyl-2-mercaptoimidazole and proton, and also to the insignificant change in the solvation state of 1MI. At higher DMSO concentrations in the solvent, an increase in the negative values of the Gibbs energy of the 1MI protonation transfer is accompanied by a predominant contribution from increased solvation of the protonated form of 1MI along with the negative contribution from resolvation of proton and 1MI. Both in water and in water–dimethylsulfoxide solvents, the silver(I) ion forms three complex species with 1MI, whose stability increases at increased DMSO contents. Stabilization of 1MI and silver ion transferred from water to the H₂O–DMSO solvents makes a negative contribution to the change in the Gibbs energy of the transfer of the monocomplex formation reaction.