Spectral and solvation effect studies on charge transfer complex of 2, 6-diaminopyridine with chloranilic acid

Charge transfer complex formation between 2,6-diaminopyridine (2,6-DAP) as the electron donor, proton acceptor, with chloranilic acid (CLA) as the pi-electron acceptor, proton donor, has been investigated spectrophotometrically in ethanol (EtOH), acetonitrile (AN) and binary mixture composed of 50% ethanol + 50% acetonitrile (v/v), (ANET). The stoichiometry of the complex has been identified by Job's, photometric and conductometric titration methods to be 1:1. Benesi-Hildebrand equation has been applied to estimate the formation constant (K-CT) and molecular extinction coefficient (epsilon), they recorded high values confirming high stability of the produced complex. Oscillator strength (f), transition dipole moment (mu), ionization potential (I-p) and dissociation energy (W) of the formed CT-complex were also determined and evaluated, they showed solvent dependency. Based on the simple composition and fast production of the CT-complex in solution, a rapid, simple and accurate spectrophotometric method for donor determination is suggested. The solid CT-complex between 2,6-DAP and CLA has been isolated and characterized using elemental analysis, FTIR and H-1 NMR measurements, it has been found that its molecular composition is 3:2 (electron donor: electron acceptor). Also, molecular modeling utilizing MM2 method including in ChemBio3D Ultra 12.0 software confirmed this molecular composition. Moreover, the present work showed the existence of proton transfer beside charge transfer in the obtained complex. (C) 2013 Elsevier B.V. All rights reserved.