Abstract
New charge transfer complex between the n- and π-donor 5-amino-1,3-dimethyl pyrazole (5-ADMP) with the π-acceptor chloranilic acid was synthesized and characterized experimentally and theoretically. The experimental work was carried out in solution and solid state. The selected solvents were chloroform (CHL), methanol (MeOH), ethanol (EtOH) and acetonitrile (AN). upon mixing the donor with acceptor a change in color takes place immediately to pink one with absorption maxima at λmax 530, 531, 530 and 522 nm in CHL, EtOH, MeOH, and AN, respectively. The complex was stable for more than 2 h. The stability constant was calculated using Bensie-Hildebrand equation where it recorded the highest value in chloroform and the least one in methanol. Thermodynamic parameters were calculated where the enthalpy of formation recorded high value in chloroform. The solid complex was prepared where elemental analysis confirmed its composition at 1:1 in concordant with that in solution. The infrared spectra of the formed complex confirmed the existence of proton transfer hydrogen bond beside charge transfer interaction. A theoretical computations using DFT at the basis set B3LYP/6-31 G(d,p) was applied to support the experimental results. Optimization energy and geometrical parameters confirmed the high stability of the complex due to the presence of CT beside PT in its chemical structure. Reactivity parameters strongly recommended that 5-ADMP is good electron donor and CLA is good electron acceptor. MEP maps confirmed the presence of proton transfer hydrogen bond where OH of CLA is the electrophile and the pyridinic-like ring nitrogen of 5-ADMP is the nucleophile. The origin of electronic spectra was computed by TD-DFT using PCM as solvation model. Two absorption maxima were recorded in the calculated spectra attributing to π-π⁎ and n-π⁎ transitions in all media. Natural population analysis was applied to estimate the natural atomic charges and natural bond orbital (NBO). Both confirmed the existence of strong proton transfer hydrogen bonding beside charge transfer in the produced complex.
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•New CT complex of 5-ADMP-CLA has been synthesized.•The complex was studied in solution and solid state.•The complex included hydrogen bonding beside CT.•DFT was applied at B3LYP/6-31 G(d,p) to compliment the experimental results.•TD-DFT was applied to explain the origin of measured electronic spectra.