Synthesis, Characterisation, Hirshfeld Surface Analysis, Magnetic Susceptibility, DFT Calculations, pkCSM Profile, and Biological Activities of Novel Mono-, Di-, and Multinuclear Cobalt (II) Complexes

This study explores the synthesis and diverse properties of newly synthesised water-soluble cobalt (II) complexes (1–3). Analysis of the complexes through various methods, including Hirshfeld surface analysis, reveals distinctive intermolecular interactions, particularly robust H-bonding contributions to crystal packing. 2D fingerprint plots provide quantitative insights into supramolecular interactions, while TGA-DSC analysis elucidates multi-step decomposition processes, mainly involving organic moieties. FT-IR and SCXRD confirm the structures of the complexes. Magnetic susceptibility measurements show paramagnetic behaviour in all complexes. FMO calculations expose HOMO-LUMO gaps and charge transfer processes, with NBO analysis emphasizing the significance of chloride, nitrogen, and oxygen atoms in coordination. In addition, pkCSM profile was carried out. The biological properties of the complexes reveal potent antibacterial activity for 2 and 3 against Gram-positive and Gram-negative bacteria. Despite lower antibacterial efficacy compared to standard antibiotics, their water solubility suggests potential human pharmacological applications. In terms of anti-inflammatory activity, all three complexes exhibit concentration-dependent prevention of ovalbumin denaturation, with 2 being the most effective. Compound 3, despite having seven carboxyl groups, exhibits the weakest anti-inflammatory effect, potentially attributed to complex formation obscuring these groups. Furthermore, all complexes display antioxidant activities; 1 and 2 are greater than BHT in the ferric thiocyanate assay.