Thermodynamic and structural studies of newly prepared CT complex between pyrazole as a donor and salicylic acid as acceptor at various temperatures in ethanol

Abstract

The equimolar mixture of salicylic acid and pyrazole was prepared to form the charge transfer complex (CTC), and crystallization was done by a slow evaporation method, which gave white rod-shaped crystals. The crystal structure shows that hydrogen bonding occurs by the transfer of aromatic hydrogen atom from salicylic acid to the nitro groups of the pyrazole which is characterized using SCXRD. Various techniques have been utilized to describe the complex, for example, UV–visible and FTIR spectroscopy. The shift in the wavenumber was shown for the CT complex compared with its reactants in FTIR spectra. Further, stoichiometry of the complex was determined using UV–visible spectroscopy at different temperatures ranging between 25°C and 45 °C by making the mixture with equimolar ratio utilizing the straight-line method known as Benesi-Hildebrand equation, found to be 1:1 in our study. Various thermodynamic and physical parameters were evaluated, such as oscillator strength (f), transition dipole moment (μEN), molar extinction coefficient (εCT), energy of interaction (ECT), and stability constant (KCT). Other parameters like Gibbs free energy (ΔG°), entropy (ΔS) and enthalpy (ΔH), were calculated using equation given by Van’t Hoff. The interaction SA and PyR was visualized via N+—H···O− hydrogen bonding. TG/DTA studies reveal information about the stability of the CTC as a function of temperature. In addition, analysis of the intermolecular interactions that stabilize the crystal packing have been performed by using Hirshfeld surfaces and their associated 2D fingerprint plots. Molecular docking studies have also been done with total binding energy of −198.53 kcal mol−1 with B-DNA.