Synthesis, spectral, DFT, and antibacterial studies of Nickel(II) and Cobalt(II) complexes with aminoantipyrine based Schiff base ligands

Abstract

Schiff base complexes are a class of molecules that have sparked a great deal of attention due to their interesting chemical and physical properties, as well as their diverse applicability in a variety of scientific fields. Schiff bases and aminoantipyrine derivatives are continuously being investigated, despite their widespread use as medicines and bioactive compounds. In this study, we present the synthesis of new Ni(II) and Co(II) Schiff base complexes [M(L1-5)2Cl2] using the following ligands: 1,5-dimethyl-2-phenyl-4-((3,4,5-trimethoxy-benzylidene)amino)-1H-pyrazol-3(2H)-one (L1), 4-((4-methoxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L2), 4-((3,4-dimethoxy-benzyli-dene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L3), 4-((1-([1,1′-biphenyl]-4-yl)ethyli-dene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L4), 4-((4-hydroxy-3-methoxy-benzylidene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L5), derived from aminoantipyrine. Various approaches, including UV, IR, NMR (1H, 13C), DFT analyses, and molar conductance measurement, have been employed to characterise freshly synthesised compounds. The antimicrobial screening results indicate that the anti-bacterial activities of the metal complexes are more active than the free ligands. All the synthesized compounds were found to be active against both Gram positive and Gram negative bacteria. Compound [Ni(L4)2Cl2] was found to show best activity. According to the reactivity parameter factors, compound Co(L2)2Cl2 has a higher value of hardness (η = 1.677 eV) and a lower value of softness (σ = 0.596 eV), It suggests that compound [Co(L2)2Cl2] is less reactive and more stable.