Synthesis, spectral studies and DFT computational analysis of hydrogen bonded-charge transfer complex between chloranilic acid with 2,4-diamino-quinoline-3-carbonitrile in different polar solvents

Abstract

Abstract New hydrogen bonded charge transfer complex (HBCT) between 2,4-diamino-quinoline-3-carbonitrile (DAQC) and chloranilic acid (CA) is synthesized and characterized experimentally and theoretically. The experimental work included the use of electronic and vibrational spectra to analyze the formed complex. Based on electronic spectra, the molecular composition was determined by Jobs and molar ratio methods in different polar solvents included acetonitrile (AN), methanol (MeOH) and ethanol (EtOH). It was found to be 1:1 (donor:acceptor) in the different solvents. Also, the formation constant of the formed complex was determined using Benesi-Hildebrand equation where it recorded high values suggesting the high stability of the formed HBCT complex. The stability of the investigated complex was further analyzed by determining different spectroscopic parameters as oscillator strength, transition dipole moment, charge transfer energy, ionization potential, dissociation energy and free energy. The solid complex was synthesized and characterized by elemental analyses where 1:1 complex is formed. The infrared spectra revealed the existence of both charge transfer and hydrogen bonding in the formed complex which is responsible for its high stability. In order to complement the experimental work, two DFT methods, B3LYP and CAM-B3LYP were used to predict the stability, molecular structure, electronic and spectroscopic properties of the studied systems. These methods were introduced, for the first time, to study the stability of the expected structures of CA conformers. The one with lower energy (high stability) included two hydrogen bonding between CA hydroxyls and neighboring carbonyl groups. Of the suggested interaction complexes between chloranilic acid (CA) and 2,4-diamino-quinoline-3-carbonitrile (DAQC), the most stable one which has the lowest energy was used to simulate the observed electronic and vibrational spectra of the CA-DACQ complex. The reactivity descriptors indicated that DAQC is the e-donor while CA is e-acceptor. Also, the most reactive electrophilic and nucleophilic sites of CA and DAQC were predicted using the molecular electrostatic potential (MEP) map. Both experimental and theoretical studies confirmed the high stability of the formed complex based on the presence of charge transfer beside proton transfer in the CA-DAQC complex.