Solvent effect on the complex formation of a crown ether derivative with sodium and potassium ions. Thermodynamic background of selectivity

The complexation properties of dimethyl-pyridino-18-crown-6 ether (M2P18C6) with Na+ and K+ in different primary alcohols including methanol (MeOH), ethanol (EtOH) and n-propanol (n-PrOH) were investigated by UV-vis spectroscopy. Stability constants and thermodynamic parameters have been determined applying the van't Hoff theory. In the cases of both Na+ and K+ the stability constants increase with decreasing permittivity of the solvent used. M2P18C6 always exhibits better affinity to K+ in each alcoholic solution compared to Na+. Thermodynamic studies suggest that in both cases there is a correlation between the permittivity of the solvent and the enthalpy and entropy change of complex formation.

Graphical abstractDownload high-res image (94KB)Download full-size imageHighlights► In alcoholic solutions the crown ether shows better affinity to K+ than Na+. ► Stability constants of complexes formed are increased at decreased permittivity. ► The permittivity correlates both with the entropy and enthalpy changes. ► Selectivity of crown ether decreases considerably at higher temperature.