Mixed‐Ligand Cu(II), Co(II), and Ni(II) Complexes of an o ‐Vanillin‐Based Schiff Base and 1,10‐Phenanthroline: Spectroscopic Characterization, Thermal Behavior, Photoluminescence, and Antimicrobial Activity

Abstract

A new series of mixed‐ligand Cu(II), Co(II), and Ni(II) complexes incorporating the bidentate Schiff base ( E )‐2‐methoxy‐6‐((phenylimino)methyl)phenol (HL) and 1,10‐phenanthroline (phen) as a co‐ligand has been synthesised and characterized. HL was prepared by condensation of 2‐hydroxy‐3‐methoxybenzaldehyde with aniline and reacted with the corresponding metal(II) acetates and phen in a 1:1:1 molar ratio. The compounds were characterized by 1 H and 13 C NMR (ligand only), elemental analysis, FT‐IR, UV–Vis, and LC–MS/MS spectrometry, TG/DTA, magnetic susceptibility and molar conductivity measurements. Spectroscopic data indicate that HL binds in a bidentate O,N‐fashion through the phenolate and azomethine donors, while phen acts as a bidentate N,N′‐donor; a monodentate acetate and a coordinated water molecule complete the proposed distorted octahedral geometry. All three complexes are non‐electrolytes in solution, as shown by the low molar conductivities measured in DMF. Thermal analysis revealed analogous multi‐step decomposition profiles terminating in putative oxide‐containing residues. Based on photoluminescence measurements conducted in a 10 −3  M methanol solution, the L‐Ni complex exhibited the highest emission. In antimicrobial assays, the L‐Cu and L‐Co complexes exhibited a moderate inhibitory effect against the tested microorganisms, with activity comparable to that of the reference antibiotics.