Solvation-thermodynamic effects of the water-methanol solvent on the coordination of Na+, K+, NH 4 + , and Ag+ ions with 18-crown-6: Gibbs energies of complexation and resolvation of reagents

The results of solvation-thermodynamic monitoring of aqueous-methanol solutions of electrolytes (NaCl, KCl, NH₄Cl, AgNO₃) and 18-crown-6 ether (L) in the mole fraction scale are summarized and systematized. The stability of sodium mono(crown ether) complexes in water-methanol solvents is due to both enthalpy and entropy contributions, and the stability of the ammonium and silver complexes, to the enthalpy contribution. The solvent effects in formation of crown ether complexes of sodium, potassium, ammonium, and silver are subjected to solvation-thermodynamic and correlation analyses. An equation is suggested for estimating the ion selectivity of crown ethers, and the contributions of energy constituents (the Gibbs energy of transfer of reagents) to varation of the ion selectivity of 18-crown-6 toward M-Na⁺ pairs in the water-methanol solvent are revealed.