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The 4f-4f absorption spectra of the simultaneous heterobimetallic complexation of trivalent neodymium ion with l-tryptophan and divalent zinc ion in aquated DMF (50%, v/v) at pH 6.0 was recorded at the time interval of 1h. From the observed absorption spectra, the values of intensity parameters such as oscillator strength (P) and Judd-Ofelt intensity (Tλ) parameters, kinetics and thermodynamics parameters were evaluated. The rate constant increases with an increase in the temperature along with the oscillator strengths and Judd-Ofelt intensity parameters. The positive values of the change in the standard enthalpy (ΔH°) and entropy (ΔS°) indicate that the complexation is endothermic. The negative values of the change in the standard free energy (ΔG°) in the range from 293.15 K to 308.15 K, indicate that the reaction occurs spontaneously and hence the formation of heterobimetallic complex in the solution is favored kinetically and thermodynamically., (Copyright © 2013 Elsevier B.V. All rights reserved.)

The interaction of gly-gly with Pr(III) and Nd(III) have been studied in different aquated organic solvents like CH(3)OH, CH(3)CN, dioxane and DMF by using 4f-4f transitions spectra. Various energy interaction parameters like Slater Condon (F(k)), Racah (E(k)), Lande (ξ(4f)), nephelauxetic effect (β), bonding (b(1/2)) and percent covalency (δ) parameters have been calculated to explain the nature of complexation. The intensity parameters like oscillator strength (P) and Judd-Ofelt parameters (T(λ), λ=2, 4, 6) also support the mode of binding of gly-gly to metal ions. The results show that Pr(III) and Nd(III) with gly-gly form complexes by ionic linkages with carboxylate anion with weak covalency. The protonation constants and metal-ligand stability constants have also been determined by potentiometric measurements in aqueous medium at different temperatures (290, 300 and 310 K) at constant ionic strength, 0.1 mol dm(-1). The results show the formation of metal-ligand complexes in the stoichiometric ratio 1:1. The stability of complexes is more in Nd(III) complexes as compared to Pr(III) complexes. Thermodynamic parameters (ΔG, ΔH and ΔS) of complexes were also calculated and the negative values of ΔG and ΔH show that the complex reactions are spontaneous and exothermic. The positive values of ΔS indicate high stability of complex reactions which are enthalpy-driven., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The absorption spectra of trivalent neodymium ion with 1,2,4-1H-triazole and 1,2,3-benzotriazole in absence and presence of calcium(II) ion in aqueous and some selected different aquated organic solvents have been recorded in the visible and near infrared regions. From the data available in the absorption spectra, various spectroscopic parameters such as Slator-Condon (F(k)), Lande spin-orbit coupling constant (ξ(4f)), nephelauxetic ratio (β), bonding parameter (b(1/2)), percent covalency (δ), oscillator strength (P) and Judd-Ofelt intensity (T(λ)) parameters have been evaluated. The Judd-Ofelt intensity, T(λ) (λ=2, 4, 6) parameters are utilized in evaluating the P(cal) from various excited states of trivalent neodymium ions and ratifying as an inner sphere complexations., (Copyright © 2011 Elsevier B.V. All rights reserved.)