Spectroscopic Study of Charge Transfer Complexes of Dibenzo-24-crown-8 (DB24C8) with Iodine in Three Chlorinated Solvents

Abstract

<em><span lang="EN-GB">Charge Transfer (CT) complexes formed between dibenzo-24-crown-8 (DB24C8) as an electron donor with the σ-electron acceptor iodine (I₂) in </span><span>chloroform, dichloromethane, and 1,2-dichloroethane solutions </span><span lang="EN-GB">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)</span><span lang="FI"> Studies on the system showed the time dependence of the absorption band of the complexes.</span><span lang="EN-GB"> The observed time dependence of the </span><span lang="FI">charge-transfer band and subsequent formation of I₃¯ 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.</span><span lang="EN-GB"> Formation constants of the resulting complexes were determined by measuring the absorbance at </span><span lang="EN-GB">l</span>_{<span lang="EN-GB">max</span>}<span lang="EN-GB"> 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 1:1 (donor : acceptor) molar ratio for both complexation system by using photometric titration measurements. The formation constant (K_CT), molar extinction coefficient (</span><span lang="EN-GB">e</span>_{<span lang="EN-GB">CT</span>}<span lang="EN-GB">), free energy change (</span><span lang="EN-GB">D</span><span lang="EN-GB">G⁰), CT-energy (E_CT), were calculated by using the Benesi-Hildebrand method. </span><span lang="EN-GB">Stability of the resulting complex in three solvents was also found to vary in the order of 1,2 -DCE >DCM> CHCl₃.</span></em>