Synthesis and spectrophotometric studies of charge transfer complexes of p-nitroaniline with benzoic acid in different polar solvents

•A charge transfer or proton transfer complex is synthesized and confirmed by spectral investigations.•Spectrophotometric studies were made in different polar solvents.•Benesi–Hildebrand equation in various solvents was used to determine KCT, εCT, and ECT of the CT complex.•Thermal analysis (TGA–DTA) was also used to confirm the thermal fragmentation and the stability of the CT complex.

The charge transfer complexes of the donor p-nitroaniline (PNA) with the π-acceptor benzoic acid (BEA) have been studied spectrophotometrically in various solvents such as acetone, ethanol, and methanol at room temperature using an absorption spectrophotometer. The outcome suggests that the formation of the CT-complex is comparatively high in less polar solvent. The stoichiometry of the CT-complex was found to be 1:1. The physical parameters of the CT-complex were evaluated by the Benesi–Hildebrand equation. The data are discussed in terms of the formation constant (KCT), molar extinction coefficient (ɛCT), Standard Gibbs free energy (ΔG0), oscillator strength (f), transition dipole moment (μEN), resonance energy (RN) and ionization potential (ID). The formation constant (KCT) of the complex was depends upon the nature of electron acceptor, donor, and polarity of solvents used. It is also observed that a charge transfer molecular complex is stabilized by hydrogen bonding. The formation of the complex has been confirmed by UV–visible, FT-IR, 1H NMR and TGA/DTA. The structure of the CT-complex is [(PNA)+ (BEA)−]. A general mechanism for its formation of the complex has also been proposed.

Graphical abstractThe charge – transfer complex was prepared and characterized by different techniques such as FTIR, 1HNMR, TGA-DTA. Spectrophotometric studies were also performed in various solvents with different polarity to calculate thermodynamic parameters. Absorption spectra of benzoic acid (1 × 10−2 M) in acetone with addition of p-nitro aniline concentrations ranging 0.01–0.05 M are shown with increasing concentrations bottom to top.Figure optionsDownload full-size imageDownload as PowerPoint slide