Structural characterization, theoretical and antibacterial study of a V-shaped, cyclohexane bridged ONNO Schiff base

Abstract

A tetradentate ONNO Schiff base bearing two chloro substituents, namely 6,6′-((1E,1′E)-(cyclohexane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-chlorophenol) (AD2C), was obtained through condensation of 3-chlorosalicyladehyde with 1,2-cyclohexanediamine. Structure elucidation was performed through physicochemical and spectroscopic analyses viz. melting point, elemental analysis, FTIR, 1H and 13C NMR, UV-Visible and single crystal X-ray diffraction. The ν(C=N) was observed at 1626 cm−1 while the azomethine proton and carbon chemical shifts appeared at 8.27 ppm and 157.56 ppm, respectively. The n‒π*(C=N) absorption band was observed at 324 nm. The crystal structure was stabilized by intramolecular hydrogen bond O˗H···N and intermolecular hydrogen bonds C˗H···O, C˗H···Cl, C˗H···π as well as π···π interactions. The existence of intermolecular interactions was confirmed through Hirshfeld analysis, showing high contribution of H⋯H contact. The B3LYP method was used to calculate the optimized structure of the molecule through density functional theory (DFT) using the 6–311++G(d, p) basis set and was found to be consistent with the X-ray diffraction value. The frontier molecular orbitals and molecular electrostatic potential of the compound investigated through DFT calculations revealed a significantly large energy gap of 4.615 eV and nucleophilic regions located at the hydroxyl groups. The compound showed no antibacterial activity against five bacterial strains namely Bacillus subtilis (ATCC 6633), Proteus vulgaris (ATCC 6380), Pseudomonas aeruginosa, Staphylococcus aureus subsp. aureus Rosenbach (ATCC 6538) and Streptococcus mutans Clarke (ATCC 700,610).