A kinetic study on substitution reactions of tridentate ligands for acetylacetonate in bis(acetylacetonato)(tetrahydrofuran)dioxouranium(VI)

Kinetics of substitution reactions of tridentate Schiff base ligands [N-(2-hydroxy-phenyl)salicylidenimine and its derivatives] for acac in UO₂(acac)₂thf (acac = acetylacetonate, thf = tetrahydrofuran) have been studied spectrophotometrically in thf. It was found that the reaction rates show the first-order dependence on the concentrations of Schiff base ligands and are accelerated with the addition of water to solvent. Apparent second-order rate constant (at 25 °C) and activation parameters (ΔH≠ and ΔS≠) are 7.52 M^-1 s^-1, 49.8 ± 3.2 kJ mol^-1, and -61.0 ± 11.0 J K^-1 mol^-1, respectively. On the basis of these results, the reaction mechanisms will be discussed. (C) 2000 Elsevier Science S.A.