X-ray, DFT, FTIR and thermal study of the antimicrobial N-benzenesulfonyl-1H-1,2,3-benzotriazole

Abstract

N-benzenesulfonyl-1H-1,2,3-benzotriazole (NBSBZT) is a compound with significant trypanocidal and bactericidal activities, which we reported previously. In this work a combined experimental and theoretical study of its structural and molecular properties is communicated. The crystal structure of NBSBZT was determined by single crystal X-ray diffraction. The molecular vibrations and behavior on heating of NBSBZT were investigated by Fourier Transform Infrared (FTIR) Spectroscopy, Differential Scanning Calorimetry (DSC), Thermogravimetry (TG) and Hot Stage Microscopy (HSM). In parallel, Quantum Chemical calculations based on Density Functional Theory (DFT) and Scaled Quantum Mechanics methods were used to determine the geometrical, energetic and vibrational characteristics of NBSBZT. The study demonstrated that NBSBZT crystallized in the triclinic space group P‾1 (No. 2) with two inversion-related molecules in the unit cell (Z = 2). Its overall molecular conformation can be described by two torsion angles, namely φ1 (N2–N1–S10–C13) = −94.5(2)° and φ2 (N1–S10–C13–C14) = 84.2(2)°. The minimum energy structures found by theoretical calculations showed φ1 = −67.6° and φ2 = 88.0° in vacuum; however, in water, the torsion angles were −77.5° and 88.7° respectively. The differences in φ1 (Δφ1 solid state-vacuum = 26.9° and Δφ1 solid state-water = 17.0°) could be attributed to the high intermolecular cohesive forces present in the crystal of NBSBZT. A good correlation between the experimental and theoretical mid-FTIR spectra was found. The DSC, TG and HSM results indicated that NBSBZT was a solvent-free solid, which melted at 128.8 °C but decomposed above 130 °C.