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.