Charge Transfer in Some Complexes of Crown Ether and of Thiacrown Ether with Dihalogens: DFT Study

The present study was carried out by focusing on the interaction between molecular complexes crown and thiacrown ethers such as 15-crown-5 (15C5), thia-15-crown-5 (T15C5), dithia-15-crown-5 (DT15C5) with homogeneous and heterogeneous dihalogens (XY) such as I-2, IBr, ICl, Br-2, Cl-2 in the gas phase and in dichloromethane solvent through applying density function theory (DFT) as well as Gaussian 98 programs series. Characteristics such as frequency, enthalpy of reaction and energy have been totally specified. Special attention was placed on the study of electronegativity of outer halogen atom and polarization of bond between two halogens on the interaction. Results indicate that electronegativity of the external halogen atom and the polarization of dihalogen bond have remarkable effects on structure parameters, donor-acceptor effect, structural stabilization, and the enthalpy of the complex product. It is concluded that the charge transfer takes place in three complexes: 15C5, T15C5, and DT15C5; and the direction of charge transfer is from crown and thiacrown molecule to dihalogen. Stability of 15C5, T15C5 and DT15C5 complexes according to the energy is ICl > IBr > I-2. The optimum condition for maximum stability of the molecular complex M ... IY is optimized plane structure and the optimum level of polarization of dihalogen during complexation of 15C5, T15C5, and DT15C5 is ICl molecule. The study of the interaction in dichloromethane solvent has similar results to the gas phase. An analysis of the NBO confirms the obtained results.