spectrophotometric study of the thermodynamics and kinetics of charge-transfer complexation of dibenzo- 18-crown-6 with iodine in chloroform solution

the charge-transfer complexation reaction between iodine and dibenzo- 18-crown- 6 (db18c6) has been studied spectrophotometrically in chloroform solution at different temperatures. the resulting donor-acceptor complex was formulated as (db 18c6…i )i . the spectrophotometric results , as well as the conductivity measurements, indicated that the gradual release of tiiodide ion from its contact ion paired form, in the molecular complex, into the solution is the rate determining step of the reaction. the rate constants at various temperatures and the activation parameters e , ?h and as were calculated. the enthalpy and entropy of the complex formation reaction were evaluated from the temperature dependence of the formation constant. it was found that the resulting charge-transfer complex is both enthalpy and entropy stabilized.