Structure elucidation {single X-ray crystal diffraction studies, Hirshfeld surface analysis, DFT} and antibacterial studies of 1,2-benzothiazine metal complexes

Abstract

The 2-benzyl-4‑hydroxy-1,1-dioxo-1,2-benzothiazine-3-carboxylic acid methyl ester i.e., ligand 1 was utilized to synthesize Mn(II) 2, Co(II) 3, Ni(II) 4, Cu(II) 5 and Zn(II) 6 derived metal complexes in mild basic conditions. The structural investigation was carried out by UV–vis, FT-IR, NMR spectroscopy, CHN analysis, conductivity measurement, ESI-MS analysis and magnetic susceptibility techniques. The X-ray diffraction analysis confirmed the octahedral and distorted square pyramidal geometries of the cobalt and copper complexes. The ligand 1 coordinated with metal centres through enolic oxygen atoms of the thiazine ring and ester group while methanol coordinated with metal center via oxygen atom. The Hirshfeld surface analysis (HSA) was utilized to determine the intermolecular interactions. In support of the experimental data, DFT studies were also performed for the cobalt and copper complexes. The NBO analysis resulted in the large stabilization values 11.91 and 12.35 kcal/mol for the cobalt and copper complexes. The global reactivity indicated the higher values of hardness and the large values of FMO analysis which support the higher stability of the metal complexes. The synthesized compounds were also evaluated against six bacterial strains to check their antibacterial potential. It was observed from results that highest activity was depicted by copper complex 5 against B. subtilis and the zone of inhibition is 23.4 ± 0.6 mm which is comparable to ampicillin (standard drug).