Trivalent Metal Complexes of Rich-Hyrdoxy Schiff base Ligand: Synthesis, Characterization, DFT Calculations and Antimicrobial Activity

Abstract

The design of trivalent metal complexes involves choosing suitable ligands that can bind to the metal and confer the desired properties. In this study, novel trivalent metal complexes (TVMCs) of Ru, Fe, and Cr were synthesized from a newly developed hydroxy-rich Schiff base ligand (LH2) derived from 4,4'-oxydianiline with 2, 4-dihydroxybenzaldehyde, which is referred to as N, N`-bis [ 2,4-dihydroxyphenyl-methylidene] 4,4'-oxydianiline (LH2). The ligand synthesis was performed using reflux without a catalyst in ethanol. The products underwent thorough characterization experimentally by various techniques such as: FT-IR, 1H-NMR, 13C-NMR, Powder XRD, elemental analysis, UV-Visible, conductivity, magnetic susceptibility, and thermal gravimetric analysis. The molar conductance measurements suggest that the complexes are non-electrolytes and do not contain conductive species outside the coordination sphere. Thus they can be formulated as [MLCl(H2O)].nH2O. Magnetic moment and electronic spectral studies confirmed that all complexes exhibit octahedral geometry around the metal ion. Furthermore, density functional theory (DFT) calculations were performed theoretically to investigate the structures, frontier molecular orbitals (HOMO and LUMO), molecular electrostatic potential (MEP), and electron localization function (ELF) for all complexes, utilizing the Gaussian09 software and the B3LYP/6-311+G(d, p) level. In vitro experiments were conducted to evaluate the antibacterial activity of the compounds against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial species, using the agar diffusion method. The results indicate that the Fe(III)-complex exhibits noteworthy inhibitory effects on both Gram-positive and Gram-negative bacteria, with a maximum inhibition zone.