Synthesis and spectrophotometric studies of charge transfer complexes of benzamide with picric acid in different polar solvents

Abstract

The charge transfer complexes of the donor benzamide (BZ) with the π-acceptor picric acid (PAH) have been studied spectrophotometrically in various solvents such as carbon tetrachloride, ethanol, and methanol at room temperature using an absorption spectrophotometer. The results indicate that the formation of a CT complex in less polar solvent is comparatively high. 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 (K CT), molar extinction coefficient (e CT), standard free energy (∆G°), oscillator strength (f), transition dipole moment (μ EN), resonance energy (R N), and ionization potential (I D). The results indicate that the formation constant (K CT) for the complex was shown to be dependent upon the nature of the electron acceptor, donor, and polarity of the solvents used. It was also observed that a charge transfer molecular complex is co-stabilized by hydrogen bonding. The formation of the complex has been confirmed by UV–Vis, FT-IR, 1H NMR, and TGA/DTA techniques. The structure of the CT complex is [(BZH)+(PA)−], and a general mechanism for its formation is also proposed.