Stoichiometric, Thermodynamic and Computational DFT Analysis of Charge Transfer Complex of 1-Benzoylpiperazine with 2, 3-Dichloro-5, 6-Dicyano-1, 4-benzoquinone

This research discusses the charge transfer (CT) complex of 1-benzoylpiperazine (1-BP) as a donor with the π-acceptor of 2, 3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) which has been studied spectrophotometrically in acetonitrile (ACN) at different temperatures. The 1:1 molecular composition of the CT complex was confirmed by applying Job’s continuous variation and photometric titration methods and the Benesi–Hildebrand equation is used to calculate the formation constant (KCT) and molar extinction coefficient (e). The thermodynamic parameters standard enthalpy (ΔH°), standard entropy (ΔS°) and standard Gibbs energy (ΔG°) were calculated by using van’t Hoff equation. These results indicate that the CT complex formation is exothermic. The computational study of the CT complex, using density functional theory, supports the experimental work. The molecular geometry, molecular electrostatic potential maps, characterization of the frontier molecular orbital surfaces, Mulliken partial atomic charges and reactive parameters of the acceptor and donor are helpful in assigning the CT route. The charge transfer in the 1-BP–DDQ complex and its high stability are evidenced through both experimental and theoretical studies.