Spectrophotometric study of charge transfer complex between 2,6-diaminopyridine and 2,5-dihydroxy-p-benzoquinone

Abstract

Charge transfer (CT) complex formation between 2,6-diaminopyridine (2,6-DAP) as the electron donor with 2,5-dihydroxy-p-benzoquinone (DHBQ) as the electron acceptor has been studied spectrophotometrically in different polar solvents at room temperature. A new absorption band due to CT complex formation was observed near 490 nm. The stoichiometric ratio 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 (ε). They recorded high values confirming high stability of the formed complex. The physical parameters, oscillator strength (f), transition dipole moment (μ), ionisation potential (I D), resonance energy (RN ) and standard free energy change (ΔG°) of the formed complex were determined and evaluated in the different solvents. The solid complex between 2,6-DAP and DHBQ has been isolated and characterised using elemental analysis, FT-IR and 1H-NMR measurements.