Inner and outer sphere complexation between europium(III) and glycine in aqueous methanol

The complexation between Eu(III) and glycine in water and aqueous methanol was studied by UV-visible spectroscopy. Substantial increases in the extent of complexation occur with increasing methanol mole fraction. Changes in the signs of the complexation enthalpy and entropy with increasing organic solvent character were interpreted in terms of increasing inner sphere complexation, coupled to the formation of outer sphere complexes, which were not present to a measurable extent in aqueous solutions. Only 1:1 complexes were found above 10% water composition, whereas a bis(glycinato) complex forms at lower water percentages.