Luminescence study on preferential solvation of Europium(III) in water/non-aqueous solvent mixtures

Abstract

The solvent composition in the first coordination sphere of Eu(III) in water/non-aqueous solvent mixtures was investigated by measuring the luminescence lifetime. The inner-sphere hydration numbers of Eu(III) calculated from the lifetimes gave reasonable values in N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, formamide, hexamethyl phosphoramide, or N-methylformamide with water system. Eu(III) was preferentially solvated by the non-aqueous solvent in those systems, over the whole range of the non-aqueous solvent mole fraction in the bulk mixtures, X s. The degree of the preferential solvation K PS, defined as the solvent/water mole ratio in the first coordination sphere to that in the bulk solution, varied considerably with the X s in all the systems. The order of the K PS for Eu(III) was hexamethyl phosphoramide>dimethyl sulfoxide> N-methylformamide> N, N-dimethylformamide>formamide> N, N-dimethylacetamide>water>pyridine>methanol>ethanol>acetone>tetrahydrofuran>acetonitrile at X s=0.5. The Gibbs free energy of transfer of Eu(III) from water to non-aqueous solvent was also estimated from the K PS.