The nature of a sodium–crown interaction studied by sodium-23 nuclear magnetic resonance and by crystal structure determination of a complex with co-ordinated solvent

Abstract

New measurements were obtained by n.m.r. methods on the relaxation times of ²³Na nuclei in ligand–metal salt solutions in pyridine–CH₂Cl₂(1 : 1) with the intention of modelling the rate processes in ion selective electrodes. Cation-exchange rates for some propeller crowns suggest the mechanism of Na exchange in the presence of excess sodium ions is dissociative. Sodium exchange rates are slower for more rigid propeller crowns. The solvated species are shown by means of a crystal structure to contain only one pyridine co-ordinated to sodium, but additional molecules of solvating pyridine are present in the crystal, and evident in elemental analyses. An additional sodium-containing species was discovered at temperatures of 230 K and below in this solvent. Results are of significance in relation to understanding the nature of cation–ionophore interaction in ion-selective electrodes and other selective devices.