investigation of substitution reaction kinetics and thermodynamics between salen and [cu(pdtc)2] complex

This study focuses on investigating the complexation process between n,n’-bis(salicylidene)ethylenediamine (salen) and the metal complex [cu(pdtc)2] in a dimethyl sulfoxide (dmso) solvent. the kinetics and thermodynamics of the substitution reaction were examined. the [cu(pdtc)2] complex and the salen ligand were synthesized using a reported method, and their absorption spectra displayed characteristic peaks consistent with previous findings. the kinetics of the cu(ii) complex were studied under pseudo-first-order conditions in dmso, with varying concentrations of salen and a constant concentration of the [cu(pdtc)2] complex. reactions were carried out at temperatures of 25 °c, 30 °c, and 35 °c. by conducting temperature-dependent studies, the activation parameters (activation energy, activation entropy, and activation enthalpy) were determined. the substitution reaction was monitored through absorption spectra measurements, revealing a reduction in the absorption peak at 435 nm and the appearance of a new absorption peak at 360 nm. the rate constants obtained for the substitution reactions of salen at 25 °c fell within the range of 0.16x10-1 1/min to 5.66x10-1 1/min, which was higher compared to previous investigations due to the size of the substituted ligand. the reaction was found to follow the first-order kinetics with respect to [cu(pdtc)2] and salen, indicating a second-order overall reaction. increasing temperature resulted in higher values of kobs and k2. the calculated activation parameters revealed a positive activation entropy, implying a dissociative mechanism, and a positive activation enthalpy, indicating an endothermic nature of the substitution reaction.