Synthesis of a new naphthol-derivate salen and spectrophotometric study of the thermodynamics and kinetics of its complexation with copper(II) ion in binary dimethylsulfoxide-acetonitrile mixtures

A synthetic procedure has been developed for the preparation of new salen (2,2'-[1,2-ethanediyl bis(nitriloethylidyne)]bis(1-naphthalenol). The thermodynamics and kinetics of complexation reaction between the new salen and Cu2+ ion were investigated spectrophotometrically in different dimethylsulfoxide-acetonitrile mixtures. Formation constant of the resulting 1:1 complex was determined from the absorbance-mole ratio data and found to increase with increasing acetonitrile content of the solvent mixtures. Enthalpy and entropy data for complexation were determined from the temperature dependence of the formation constant. In all solvent mixtures, the salen-copper complex is entropy stabilized but enthalpy destabilized. Order of reaction, rate constants and activation parameters for the complexation reaction in different solvent mixtures were also investigated. The Arrhenius plots showed a distinct isokinetic temperature at about 88 oC, at which the reaction rate is approximately independent of the solvent composition. Activation parameters are strongly solvent dependent.