Luminescence study on hydration states of lanthanide(III)-polyaminopolycarboxylate complexes in aqueous solution

The hydration states of lanthanide (Ln)(III) complexes (Ln=Sm, Eu, Tb and Dy) with a series of polyaminopolycarboxylate ligands were evaluated in detail on the basis of the linear correlation between the luminescence decay constants k(obs) and the inner-sphere hydration number N-H2O in D2O-H2O solutions. The k(obs) of Ln(III) complexes in D2O showed that these ligands were not effective in causing non-radiative de-excitation of the excited states for these ions. The N-H2O of Sm(III) in a certain polyaminopolycarboxylate complex was apparently larger than those of Eu(III), Tb(III) and Dy(III) in the complexes. These results suggest that the empirical formulae proposed in this study are valid for the calibration of k(obs) vs. N-H2O and that the total coordination number, i.e. the sum of the number of ligand donor groups and the N-H2O of Sm(III) is possibly unity larger than those of Eu(III), Tb(III) and Dy(III) in the complexes. (C) 1998 Elsevier Science S.A.