Laser-Induced Luminescence Study of Samarium(III) Thiodiglycolate Complexes

Abstract

studies of hydration structure for lanthanides. The fact that many f-element salts which have relatively large lattice energies are fairly soluble in water is a reflection of the strength of the interactions between the metal cations and water molecules. In turn, this strong hydration competes with complexation by ligand as the process of complexation involves the displacement of one or more water molecules by a ligand. The techniques for studying the size and/or structure of the hydration sphere can be classified as direct or indirect methods. The direct methods include X-ray and neutron diffraction, extended X-ray absorption fine structure (EXAFS), nuclear magnetic resonance (NMR) relaxation measurements, luminescence decay. The indirect methods involve compressibility, NMR exchange and adsorption spectroscopy measurements. 15 The luminescence of trivalent lanthanides has presently extensively attracted in a variety of complexes in solution with much attention. This includes the determination of the local structures in crystalline materials, glasses, and solutions. The luminescence intensity and lifetime of trivalent lanthanide (Ln) and actinide (An) ions has been used to gain information on the composition and structure of the first coordination sphere of these ions in solution in materials ranging from inorganic compounds to systems of biological interest. 16 The luminescence lifetime of Ln and An is related to N H2O (the number of H2O molecules in the primary coordination sphere of the metal ion) due to the energy transfer from the excited state of the metal ion to the O-H vibration of the coordinated water molecules. A correlation between the luminescence decay constant kobs (the reciprocal of the excited state lifetime) and the NH2O of trivalent lanthanide (Ln) and actinide (An) ions has therefore been investigated to establish a method for determining the NH2O from measurements of the luminescence lifetime. 17 The calibration relations were derived on the basis of the linear correlation of the luminescence decay constant kobs vs. volume percentage of H2O in D2O-H2O solutions and the inner-sphere hydration number N H2O in