Co(II), Mn(II), and Fe(III) complexes of water‐soluble hydrazone bearing 2‐nicotinoylhydrazineylidene moiety: Preparation, characterization, cyclic voltammetry, computational and biological studies

A water‐soluble hydrazone ligand bearing 2‐nicotinoylhydrazineylidene moiety, sodium 4‐hydroxy‐3‐([2‐nicotinoylhydrazineylidene]methyl) benzenesulfonate (NaH 2 NH), and its complexes with Co(II), Fe(III), and Mn(II) have been synthesized and characterized. The structure of the ligand and its complexes were analyzed using various spectroscopic techniques such as FT‐IR, 1 H‐ and 13 C‐NMR, EI‐mass, powder X‐ray diffraction, UV–visible spectra, and magnetic measurements. The infrared spectra indicated that the ligand behaves as a negatively charged bidentate ligand (ON) through the deprotonation of the enolic (OH) group and the azomethine (C=N) group in the [Co (NaHNH) 2 (H 2 O) 4 Cl 2 ].3H 2 O complex. In the [Fe (NaNH) 2 (H 2 O)Cl].2H 2 O complex, the ligand behaves as bi‐negative tetradentate (O 2 N 2 ) through the protonation of the enolic oxygen and the nitrogen atom of the azomethine group in two nicotinic hydrazone molecules. Another coordination type was observed for [Mn (NaNH)(H 2 O) 3 ] complex in which NaH 2 NH acts as bi‐negative tridentate ONO through the nitrogen atom of the azomethine group, the protonated of enolic and phenolic groups. The fluorescence spectrum of the NaH 2 NH was found to be quenched upon addition of these Co(II) and Mn(II) ions. The antimicrobial results indicated that the Mn(II) complex exhibited the highest antibacterial potency against all targeted organisms. The results of antioxidants demonstrated that the complexes exhibited higher activity compared to the free ligand, indicating an enhancement of antioxidant activity through complexation. The tested substances established strong nuclease‐like activity at a high concentration of 7.5 mM, leading to the complete degradation of DNA as observed in agarose gel electrophoresis. This suggests that these compounds have the potential to serve as antitumor agents in vivo by inhibiting DNA replication in cancer cells and preventing tumor growth. The interaction of the isolated compounds with 1c14 and 6vj3 targets was discussed using molecular docking.