Metal Complexes of a Novel Unsymmetrical π‐Conjugated N‐Donor Ligand: Synthesis, Characterization, DFT Studies, and Antimicrobial Activity

ABSTRACT A novel unsymmetrical π‐conjugated tetrazo ligand, ( E , Z )‐1‐(4‐ethoxyphenyl)‐3‐(2‐hydroxyphenyl)‐5‐phenylformazan ( HL ), and its Co(II), Ni(II), and Cu(II) complexes were synthesized and characterized by elemental analysis, UV–vis, FT‐IR, EPR spectroscopy, cyclic voltammetry, thermogravimetric analysis, and magnetic susceptibility measurements. The formulae of the isolated solid complexes were assigned as [Co(L) 2 ] ( 1 ), [Ni(L) 2 (H 2 O) 2 ] ( 2 ), and [Cu(L) 2 ]·0·5H 2 O) ( 3 ), where L represents the deprotonated form of HL . DFT calculations at the B3LYP/6‐31G(d)/LANL2DZ level provided insight into their electronic structures. The complexes are paramagnetic, as confirmed by magnetic moment and EPR data, while thermal analysis indicated superior stability for complex 2 . Electrochemical studies revealed quasi‐reversible one‐electron redox processes, enabling estimation of HOMO–LUMO energy gaps. In vitro antimicrobial evaluation using the agar well diffusion method against four bacterial ( Klebsiella pneumoniae , Serratia marcescens , Streptococcus pyogenes , and Staphylococcus aureus ) and two fungal ( Candida albicans and Aspergillus niger ) strains showed that HL and complex 2 exhibit remarkable antifungal activity against A. niger , surpassing the reference drug clotrimazole. In silico ADMET analysis indicated favorable pharmacokinetic and drug‐likeness profiles for HL , suggesting its potential as a promising lead compound. These findings collectively underscore the potential of HL and complex ( 2 ) as candidates for further development in antimicrobial and pharmaceutical applications.