Spectroscopic Study of Charge Transfer Complexes of Dibenzo-۲۴-crown-۸ (DB۲۴C۸) with Iodine in Three Chlorinated Solvents

Charge Transfer (CT) complexes formed between dibenzo-۲۴-crown-۸ (DB۲۴C۸) as an electron donor with the σ-electron acceptor iodine (I۲) in chloroform, dichloromethane, and ۱,۲-dichloroethane solutions have been studied by different spectroscopic techniques at room temperature. The spectral studies of the complexes were determined by UV-Visible, Fourier Transform InfraRed (FT-IR) Studies on the system showed the time dependence of the absorption band of the complexes. The observed time dependence of the charge-transfer band and subsequent formation of I۳¯ in solution were related to the slow transformation of the initially formed outer complex to an inner Electron Donor-Acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form three iodide ion. Formation constants of the resulting complexes were determined by measuring the absorbance at lmax for a series of solutions with varying excess amounts donor and constant iodine concentration in solvent systems used. The reaction stoichiometry was found to be ۱:۱ (donor : acceptor) molar ratio for both complexation system by using photometric titration measurements. The formation constant (KCT), molar extinction coefficient (eCT), free energy change (DG۰), CT-energy (ECT), were calculated by using the Benesi-Hildebrand method. Stability of the resulting complex in three solvents was also found to vary in the order of ۱,۲ -DCE >DCM> CHCl۳.

کلیدواژه ها:

Charge-transfer complex ، Crown ether ، Iodine ، spectroscopy