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Kinetic Studies of the Ligand Substitution Reaction of Some New Uranyl Schiff Base Complexes with Tri‐ n ‐butylphosphine
Author(s) -
Asadi Zahra,
Asadi Mozaffar,
Firuzabadi Fahimeh Dehghani
Publication year - 2013
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20815
Subject(s) - chemistry , uranyl , schiff base , reaction rate constant , solvent , steric effects , acetonitrile , associative substitution , substitution reaction , ligand (biochemistry) , entropy of activation , reaction rate , solvent effects , molecule , medicinal chemistry , inorganic chemistry , kinetics , stereochemistry , organic chemistry , catalysis , ion , biochemistry , physics , receptor , quantum mechanics
Kinetics of the substitution reaction of solvent molecule in uranyl(VI) Schiff base complexes by tri‐ n ‐butylposphine as the entering nucleophile in acetonitrile at 10–40°C was studied spectrophotometrically. The second‐order rate constants for the substitution reaction of the solvent molecule were found to be (8.8 ± 0.5) × 10 −3 , (5.3 ± 0.2) × 10 −3 , (7.5 ± 0.3) × 10 −3 , (6.1 ± 0.3) × 10 −3 , (13.5 ± 1.6) × 10 −3 , (13.2 ± 0.9) × 10 −3 , (52.9 ± 0.2) × 10 −3 , and (88.1 ± 0.6) × 10 −3 M −1 s −1 at 40°C for [UO 2 (Schiff base)(CH 3 CN)], where Schiff base = L1–L8, respectively. In a temperature dependence study, the activation parameters Δ H # and Δ S # for the reaction of uranyl complexes with PBu 3 were determined. From the linear rate dependence on the concentration of PBu 3 , the span of k 2 values and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the solvent substitution. By comparing the second‐order rate constants k 2 , it was concluded that the steric and the electronic properties of the complexes were important for the rate of the reactions.