Preferential solvation of the europium(III) ion in water–non-aqueous solvent mixtures. A luminescence lifetime study

Abstract

For binary aqueous solvent mixtures the solvent composition in the first solvation sphere of Eu³⁺ has been determined at 25 °C by measuring the luminescence lifetime. In the systems water–acetone, water–acetonitrile and water–1,4-dioxane the first solvation sphere of Eu³⁺ is exclusively occupied by water molecules even at bulk-phase mole fractions of water as low as 0.1. Eu³⁺ is preferentially solvated by water in water–methanol and by DMSO in water–DMSO mixtures over the whole range of solvent composition. In water–DMF mixtures Eu³⁺ is preferentially solvated by DMF when the mole fraction of DMF is below 0.7 and by water when it is above that value. In all the systems the degree of preferential solvation varies considerably with solvent composition. These results for the preferential solvation of Eu³⁺ are compared with those of Al³⁺ and of alkali-metal ions obtained by the n.m.r. method.