Donor-acceptor complex of 1-benzoylpiperazine with p-chloranil: Synthesis, spectroscopic, thermodynamic and computational DFT gas phase/PCM analysis

A new charge transfer (CT) complex is formed between the n- and pi-donor 1-Benzoylpiperazine (1-BNZP) with pi- acceptor p-chloranil (CHL). The CT-interaction is characterized in the defined polar solvent (acetonitile: ACN) at different temperatures. The 1:1 composition of the CT complex is proved. Benesi-Hildebrand method is used to find the stability constant (K-CT) and molar extinction coefficient (epsilon). The more stability of CT complex is suggested from observed results. The thermodynamic parameters (Delta H degrees and Delta S degrees) were calculated by using Van't Hoff plot. From these values, CT complex formation process is found to be endothermic and spontaneous. FT-IR study gives information about stretching frequencies of mono substituted product of CT complex. TGA-DTA study is used for thermal stability of product. Morphology study is used to estimate the size and structure of the product. EDX spectrum is used for elemental analysis in the stoichiometric ratio. Theoretical investigation of the CT complex using DFT and TD-DFT also supports the experimental work. The C=O bond length of CHL increases on complexation with 1-BNZP along with significant amount of charge transfer from donor to acceptor. The HOMO-LUMO computation for protonated form of complex suggests a mono substituted product is formed via inner sigma (sigma) complex. (C) 2019 Elsevier B.V. All rights reserved.