NMR study of exchange kinetics of the lithium ion with cryptand C222 in binary acetonitrile-nitromethane mixtures

The exchange kinetics of the lithium ion with cryptand C222 were studied in acetonitrile-nitromethane mixtures by lithium-7 NMR line-shape analysis. In all solvent mixtures used, and over the entire temperature range studied, the chemical exchange of the Lit ion between the solvated and complexed sites was found to occur via a bimolecular mechanism. The activation parameters E-a, Delta H double dagger, Delta S double dagger and Delta G double dagger for the exchange have been determined. The free energy barrier for the exchange process appears to be nearly independent of the binary mixture composition. The results confirm the preferential solvation of the lithium ion with acetonitrile in the binary mixed solvent systems used.