Anomalous concentration dependence of the inner-sphere hydration number change in aqueous europium(III) chloride and gadolinium chloride solutions

Structural and thermodynamic aspects of hydration of Gd(iii) systems

A first systematic experimental study on the thermodynamic description of the hydration equilibrium of Gd(iii) compounds is presented.

Photoexcitation of europium(III) in various electrolytes: Dependence of the luminescence lifetime on the type of salts and the ionic strength

The fluorescence characteristics (lifetime, excitation and emission spectra) of aqueous solutions of Eu(III) containing various supporting electrolytes such as HCl, NaCl, LiCl, CsCl, MgCl2, HClO4 and NaClO4 have been measured. The observed lifetime variations cannot be properly described neither through the hydration sphere phenomenological approach nor through a Stern–Volmer relationship. Long-range interactions between the excited ion and solvent molecules, in addition to an outer-sphere complexation with the anions, are proposed to account for the observed variations.

Raman Study of the Coordination Structure of a Rare Earth−Acetate Complex in Water

The Raman spectra of aqueous LnCl(3) x 20H(2)O x CH3(C)OOLi (LnCl(3), rare earth chloride) solutions have been measured in the liquid state. The change of the Raman symmetric Ln(3+)-OH(2) stretching band (v(w)) showed that the decrease in the ionic radius of rare earth (Ln(3+)) ions induces a change in coordination number of the Ln(3+) ion. The two peaks at 946 and 958 cm(-1) of the C-C stretching band (v(CC)) of the acetate ion are assigned to the bidentate ligand and the polymeric chain structure, respectively. The coordination structure of the acetate ion to Ln(3+) ion prefers the bidentate ligand to the polymeric chain structure throughout the rare earth series. The fraction of the bidentate ligand increases with decreasing ionic radius of the Ln(3+) ion. On the basis of the analyses of the v(w) and v(CC) bands, the change in the coordination number of the Ln(3+) ion is mainly due to the structural change (from the polymeric chain structure to the bidentate ligand) of the Ln(3+)-acetate complex rather than a elimination of one water molecule. Our results show that the Ln(3+) ions tend to form the bidentate ligand rather than the divalent (M(2+)) ions.

Coordination chemistry of trivalent lanthanide and actinide ions in dilute and concentrated chloride solutions

We have used EXAFS spectroscopy to investigate the inner sphere coordination of trivalent lanthanide (Ln) and actinide (An) ions in aqueous solutions as a function of increasing chloride concentration. At low chloride concentration, the hydration numbers and corresponding Ln,An-O bond lengths are as follows: La3+, N = 9.2, R = 2.54 A; Ce3+, N = 9.3, R = 2.52 A; Nd3+, N = 9.5, R = 2.49 A; Eu3+, N = 9.3, R = 2.43 A; Yb3+, N = 8.7, R = 2.32 A; Y3+, N = 9.7, R = 2.36 A; Am3+, N = 10.3, R = 2.48 A; Cm3+, N = 10.2, R = 2.45 A. In ca. 14 M LiCl, the early Ln3+ ions (La, Ce, Nd, and Eu) show inner sphere Cl- complexation along with a loss of H2O. The average chloride coordination numbers and Ln-Cl bond lengths are as follows: La3+, N = 2.1, R = 2.92 A; Ce3+, N = 1.8, R = 2.89 A; Nd3+, N = 1.9, R = 2.85 A; Eu3+, N = 1.1, R = 2.81 A. The extent of Cl- ion complexation decreases going across the Ln3+ series to the point where Yb3+ shows no Cl- complexation and no loss of coordinated water molecules. The actinide ions, Am3+ and Cm3+, show the same structural effects as the early Ln3+ ions, i.e., Cl- ion replacement of the H2O at high chloride thermodynamic activities. The Clion coordination numbers and An-Cl bond lengths are: Am3+, N = 1.8, R = 2.81 A; Cm3+, N = 2.4, R = 2.76 A. When combined with results reported previously for Pu3+ which showed no significant chloride complexation in 12 M LiCl, these results suggest that the extent of chloride complexation is increasing across the An3+ series. The origin of the differences in chloride complex formation between the Ln3+ and An3+ ions and the relevance to earlier work is discussed.