Effect of a Medium on Complexation between Cations
and Crown Ethers

N. V. Bondarev, E. N. Kabakova, S. V. El’tsov, and I. S. Zaitseva

Karazin National University, pl. Svobody 4, Kharkov, 61170 Ukraine

Abstract—A comparative quantitative analysis of the effects of aqueous organic solvents (water–methanol,
water–propan-2-ol, water–acetonitrile, water–dioxane, and water–acetone) on the complexation between
sodium, potassium, and ammonium cations and 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6), and dicy-
clohexyl-18-crown-6 (DCH18C6) ethers was performed in terms of thermodynamic and empirical approaches.
In solution, the crown ethers studied form enthalpy-stabilized complexes and complexes with mixed enthalpy-
entropy stabilization. The thermodynamic parameters of reagent solvation can affect the stability of NH₄⁺, Na⁺,
and K⁺ complexes with crown ethers in five ways. It was demonstrated that a changed stability of potassium
coronates in water–methanol mixtures is differently contributed by the structure-sensitive parameters of com-
plexation (the enthalpy and entropy of reagent solvation). Changes in the conformational Gibbs energy of sol-
vation of 18C6 and DB18C6 were calculated. Thermodynamic aspects of hypothetical processes in cation
extraction with crown ethers were considered. Stabilization of ammonium, sodium, and potassium coronates in
aqueous organic solvents was explained, in terms of the nonthermodynamic concept of linear free-energy rela-
tions, by a decreased cohesion energy density of solvents.

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