Thermodynamics of complex formation and solvation in the system NaCl-18-crown-6-water-dioxane

Stability constants of Na+ complexes with 18-crown-6-ether and thermodynami c characteristics of the complex formation in water and mixed water-dioxane solvents (0.2, 0.4, 0.6, and 0.8 wt. fraction of dioxane, 283-318 K) were determined by the method of EMF of galvanic circuits without transfer. Comp arative thermodynamic analysis of the complex 18-crown-6Na(+) formation rea ctions in water-dioxane, water-acetonitrile, water-acetone, water-methanol, and water-2-propanol mixtures was carried out. Contributions of the Gibbs energies of transfer (DeltaG(t)) of 18-crown-6Na(+), Na+, and the ligand to the increase in the stability of the complexes on replacement of water by mixed water-dioxane solvents were estimated. It was shown that the increase in the stability of sodium crown ether complexes primarily depends on solv ation of the complex cation and desolvation of the central cation. Changes in the conformational Gibbs energy of the ligand and quantitative parameter s of selective solvation of the reagents were estimated.