Thermodynamics of reactions of stepwise complex formation of silver(I) ion with pyridine in binary solvents.

• Replacing MeOH with AN leads to decrease/increase in the exothermicity formation of [AgPy]+/[AgPy 2 ]+. • Changes in Δ tr H 0(r 1)/Δ tr H 0(r 2) are due mainly to a contribution from starting reagents/reaction products resolvation. • Ions and ligand solvation gives opposite contributions in the thermodynamic characteristics of complex formation reactions. • Solvation effects [Δ tr H 0([AgPy]+) – Δ tr H 0(Py)] and Δ tr H 0(Ag+) are proportional to each other with a coefficient k. • For pairs of «amphoteric – basic» solvents, a correlation between their physicochemical properties and k values was found. In this study, the enthalpies of stepwise complexation reactions between silver(I) ions and pyridine in methanol–acetonitrile mixed solvents (MeOH-AN, with molar fractions of AN varying from 0 to 1) were determined by the calorimetric method at 298.15 K. The analysis of the solvation contributions of the reactants to the alterations in the thermodynamic characteristics associated with the formation of [AgPy]+ and [AgPy 2 ]+ complexes as the solvent composition transitions, i.e. from methanol to its mixtures with acetonitrile (MeOH → χ AN), from methanol to its mixtures with N,N -dimethylformamide (MeOH → χ DMF) and from acetonitrile to its mixtures with dimethyl sulfoxide (AN → χ DMSO) was carried out. The research methodology was based on the provisions of the solvation-thermodynamic approach, based on the relationship between changes in the thermodynamic characteristics of the reactions of complex formation and solvation of reagents with a change in the composition of the solvent. [ABSTRACT FROM AUTHOR]