Diverse coordination of isoniazid hydrazone Schiff base ligand towards iron(III): Synthesis, characterization, SC-XRD, HSA, QTAIM, MEP, NCI, NBO and DFT study

Abstract A new iron(III) complex has been successfully prepared by the reaction of an ONO donor Schiff base, derived by condensing isoniazid and 3-ethoxysalicylaldehyde, with Fe(acac)3. The structure of the complex was explored spectroscopically through FT-IR, UV-Vis, PXRD and by elemental composition (CHN) through combustion analysis. The structure of the complex was explored by using single crystal X-ray crystallographic studies. It was revealed from the diffraction studies that both the keto and enol tautomeric forms of the ligand are present simultaneously in the Fe(III) complex. X-ray results showed that one of the ligands, due to keto-enol tautomerization, is doubly deprotonated and coordinated to the metal center through one nitrogen and two oxygen atoms, while the other ligand behaves as a monoanionic moiety and is coordinated via phenolic oxygen, iminic nitrogen, and oxygen of the carbonyl group. Furthermore, it was also investigated by diffraction studies that the Fe(III) centre adopts a distorted octahedral geometry. HSA, QTAIM, MEP, and NCI calculations were performed to explore the presence of different kinds of non-covalent interactions. NBO analysis was also used to show the donor-acceptor interactions between the HOMO and LUMO of the molecule. Theoretical calculations performed by DFT at the B3LYP/Def2-TZVP method show that the theoretically calculated results are in close association with the experimental outcomes.