A spectrophotometric and thermodynamic study of the charge-transfer complexes of iodine with 2-aminomethyl-15-crown-5 in chloroform and 1,2-dichloroethane solutions

Interaction of 2-aminomethyl-15-crown-5 (AM15C5) with iodine has been investigated spectrophotometrically in chloroform and 1,2dichloroethane (1,2-DCE) solutions. The observed time dependence of the charge-transfer band and subsequent formation of I-3 in solution were related to the slow transformation of the initially formed 1: 1 AM1 5C5 center dot I-2 outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants were evaluated from the absorbance- and conductivity-time data. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. Thermodynamic parameters, Delta H degrees and Delta S degrees, of the complexes have been determined from the temperature dependence of stability constants by Van't Hoff equation. The results indicate that iodine complexes of AM I 5C5 in both solvents are enthalpy stabilized but entropy destabilized. The influence of solvent properties on the kinetics and stability of the resulting charge-transfer complexes are discussed. (c) 2006 Elsevier B.V. All rights reserved.