Synthesis, characterization, antibacterial activity, and computational studies of novel Co(II) complex of saccharin ligand

Abstract

   This study aims to synthesize an octahedral cobalt (II) complex coordinated with saccharin and water ligands. The resulting complex, [Co(sac)₂(H₂O)₄].H₂O, was obtained by reacting one equivalent of CoCl₂·6H₂O with two equivalents of sodium saccharin (Nasac) in a mixed ethanol-water solvent. The complex was characterized using FT-IR, single-crystal X-ray diffraction analysis, electronic spectroscopy, molar conductivity measurement, and theoretical studies, including noncovalent interactions, density functional theory (DFT), natural bond orbital (NBO) analysis, and surface analysis (MEP and Hirshfeld analysis). Characterization data and crystal structure analysis confirmed that the cobalt (II) center was coordinated to two saccharin nitrogen atoms and four water oxygen atoms in an octahedral geometry, with an additional water molecule positioned outside the coordination sphere. Molar conductivity measurements indicated that the complex behaves as a non-electrolyte in solution. The antibacterial activity of Nasac (sodium saccharin) and its cobalt complex was assessed against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli using the agar diffusion method. The results indicated that both Nasac and the Co(II) complex exhibit good antibacterial activity against the tested bacteria. Theoretical studies such as noncovalent interaction displayed (O3…O2W, O2W‒H2W1…O1, O1‒WH1w1…O2), (O1W‒H1WA…O2, O2…O2) and (π…π [C3…C6 & C2…C4]) interactions. It suggests that all the contacts are purely noncovalent. According to density functional theory (DFT), the Co(II) complex is less reactive and more stable than the Nasac ligand. A significant transfer of charge density from the saccharin ligand to the cobalt ion was shown by neutral bond orbital (NBO) studies. According to Hirshfeld surface analysis (HAS), the near H...O/O...H contacts account for 42.0 % of the total primary intermolecular interactions in the cobalt complex, which is the largest contribution.