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.