Acid-base equilibria of some salicylatopentaminecobalt (III) ions in mixed solvent media: An attempt to study molecular recognition

Abstract

The study of the acid-base equilibria of <i>cis</i>-[Co(en)₂(RNH₂)O₂CC₆H₄OH]²⁺] (R=H, CH₃, CH₃CH₂) in methanol-water, propan-2-ol-water, terr-butanol-water, acetone-water, and ethylene glycol-water (0 <img src='http://www.niscair.res.in/jinfo/lessequals.gif' border=0> vol% organic solvent <img src='http://www.niscair.res.in/jinfo/lessequals.gif' border=0> 70) are reported at 25°C. The transfer free energy of the phenol fonn relative to that of phenoxide form of the complexes, where transfer occurs from water to the- mixed solvents, have been evaluated. Solubility studies for the sparingly soluble dithionate salt of the phenol form of these complexes have been made in methanol-water media at 25°C and the transfer free. energy of the phenol and phenoxide species (relative to water) have been assessed. Results highlight theelectrostatic and nonelectrostatic medium effects on the solvation of the phenol and phenoxide species of the complexes. The transfer free energy data suggest that the complex ions recognise the cosolvent molecules in their Gurney cosphere via both coulombic and hydrophobic interactions.