Synthesis, Structural, Molecular Docking, DFT, Vibrational Spectroscopy, HOMO-LUMO, MEP Exploration, antibacterial and antifungal activity of new Fe(III), Co(II) and Ni(II) hetero-ligand complexes

•New FeLphen, Colphen and Nilphen complexes were synthesized, characterized and theoretically investigated.•Optimization and vibrational study of the new compounds were performed using DFT approach.•The reactivity of the new compounds was evaluated using frontier orbitals studies.•In vitro evaluation of the synthesized compounds shows a good antimicrobial activity.•Molecular docking against 2VF5, 4FXQ, and 3cku was explored.•The experimental results are in good agreement with the theoretical investigation. Three new FeLphen, CoLphen and NiLphen hetero-ligand were synthesized, characterized and theoretically investigated. The new complexes were based on phenylalanine (Hphen) and 1-{(E)-[(4-methylphenyl)imino]methyl}-2-naphthol Schiff-base (HL). The results showed interesting structural variety as octahedral for FeLphen ([Fe(L)(phen)(Cl)(H2O)]), CoLphen ([Co(L)(phen)(H2O)2]) and tetrahedral for NiLphen ([Ni(L)(phen)]). The molecular properties, geometric optimization, vibrational, frontier molecular orbital, and energy evaluation of the new complexes were characterized theoretically using density functional theory (DFT) approach. The calculations were performed to find out the most reliable cis/trans (Chloride and/or H2O) and the (HL/Hphen) orientations around the Fe(III)/Co(II) and Ni(II) center. The calculations revealed that trans-H2O/Cl-cis-NHL/NHphen & cis-H2O/H2O-cis-NHL/NHphen and cis-NHL/NHphen were the most stable orientations for the FeLphen, CoLphen and NiLphen, respectively. Furthermore, the antibacterial and antifungal activity of the titled compounds was in vitro screened. The results showed that the metal complexes exhibited higher pathogenic effect than the free ligands against the selected microbes. Molecular docking investigation against 2VF5, 4FXQ, and 3cku, was carried out to provide deep insights into their role in inhibiting the growth of pathogenic microbes. Comparative analysis elucidated higher antibacterial and antifungal activity of the titled compounds compared with literature survey. [Display omitted]