Interactions between metal cations and the ionophore lasalocid. Part 7.—Heat capacities and volumes of complexation of lasalocid with alkali-metal and alkaline-earth-metal cations in methanol

Abstract

Volume changes and heat-capacity changes for the formation in methanol of the 1–1 complexes of the ionophore lasalocid anion with either the alkali-metal cations or the alkaline-earth-metal cations have been obtained from density and calorimetric measurements. The data obtained are discussed in relation to what is known about the structure of these various complexes in solution. The peculiar behaviour of lithium and magnesium ions with respect to the other cations in each series is stressed, heat capacity–entropy correlations being particularly significant. In agreement with the structural features, this could be due to the fact that in these particular complexes, the ligand has more degrees of freedom and that the cation and possibly the carboxylate group of the ligand remain more solvated. Complexation volumes and heat capacities of the other cations vary more or less regularly depending on the size and charge of the cation.