Abstract
Charge transfer (CT) complex formation between 4-dimethylaminopyridine (4-DMAP) as the electron donor and 2,5-dihydroxy-p-benzoquinone (DHBQ) as the π-electron acceptor has been investigated spectrophotometrically in methanol (MeOH), ethanol (EtOH) and acetonitrile (AN). The stoichiometry of the complex has been identified by Job's and photometric titration methods to be 1:1. The Benesi-Hildebrand equation has been applied to estimate the formation constant (K
CT
) and molecular extinction coefficient (ε). It was found that the value of K
CT
is larger in AN than in MeOH and EtOH. The thermodynamic parameters are in agreement with the K
CT
values in that the enthalpy of formation (−ΔH) has a larger value both in EtOH and MeOH than in AN, suggesting higher stability of the complex in EtOH. The complex formed between 4-DMAP and DHBQ has been isolated as a solid and characterised using elemental analysis, FTIR and
1
H NMR measurements. Moreover, it has been found that the formed complex involves proton transfer in addition to CT.