Synthesis, characterization and DFT investigation of new metal complexes of Ni(II), Mn(II) and VO(IV) containing N,O-donor Schiff base ligand

In this work, a bidentate Schiff base ligand (HL ) containing N and O as donor heteroatoms has been used to synthesize series of new stable metal complexes of general composition of M(L)(2) with M = Mn, Ni and VO. This ligand was obtained from condensation of 2-methoxybenzylamine on 2,3-dihydroxybenzaldehyde in methanolic solutions in which its complexes were obtained by mixing the corresponding metal acetate salt and the ligand in 1:2 molar ratio. The resulting three complexes have been characterized by different analytical techniques like FT-IR, UV-Vis, mass spectroscopy, thermogravimetry and cyclic voltammetry, to identify their molecular structures and redox/electrochemical properties. Moreover, the effect of the metal on the complexes electronic properties with their reactivity has also been studied by Density Functional Theory (DFT). The stable structures were optimized by using the hybrid B3LYP/6-31 G method. The spectroscopic data obtained suggest that the metal is bonded to the ligand through the phenolic-like oxygen and the imine-type nitrogen atoms. Electronic and vibrational absorption spectra of the nickel complex was found to be of square-planar geometry while square pyramidal and octahedral geometries have been proposed for VO(IV) and Mn(II) complexes, respectively. The thermogravimetric analyses of these complexes confirmed the presence of water molecules in their structures and thermal decomposition led to the formation of metal oxides as the latest residues. The voltammogram of the Ni(II) complex suggests the existence of quasi-reversible redox system in DMSO solution. (C) 2021 Elsevier B.V. All rights reserved.