Spectroscopic Study of Charge-Transfer Complexation of Iodine with DB18C6 in Chloroform, Dichloromethane and Their 1:1 Mixture

摘要

The charge-transfer complexes of dibenzo-18-crown-6(DB18C6) (L) with iodine, as a typical sigma-acceptor, were studied spectrophotometrically in chloroform, dichloromethane and their 1:1 (v/v) mixture at 25.0 +/- A 0.1 A degrees C. Spectral data, formation constants and the effect of the solvent have been determined. Spectral characteristics and formation constants are discussed in the terms of donor molecular structure and solvent polarity. The stoichiometry of the complexes was established to be 1:1. The formation constants (K (CT)) of the complexes were determined. The complexes were isolated and characterized by FTIR and H-1-NMR spectroscopy. The observed time dependence of the charge-transfer band and subsequent formation of in solution were related to the slow transformation of the initial 1:1 L:I-2 outer complex to an inner electron donor-acceptor complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants for the transformation process were evaluated in different solvent systems.