Spectroscopic studies, TD/DFT calculations, electrochemical, antibacterial, and Hirshfeld surface analysis of Ni(II) and Co(III) complexes based on 3-ethoxy salicylaldehyde

Abstract

The ligand 2-(3-ethoxy-2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazolin 3-oxide (HL1, H is the deprotonatable hydrogen) has been synthesized, and two metal complexes, namely [Ni(L2)2]·2CH3OH (1) and [Co(L2)2]·NO3·H2O (2) (where HL2 =1-(2-{[(E)-(3-ethoxy-2-hydroxybenzylidene]amino} phenyl)ethanone oxime) were obtained via complexation reaction between HL1 and nickel(II) acetate tetrahydrate or cobalt(II) nitrate hexahydrate. HL1 and both complexes were characterized by elemental analysis, as well as compared by spectroscopic methods such as FT-IR, UV–Vis and fluorescence spectroscopy. X-ray crystallography revealed that both complexes have distorted octahedral geometries but with a different configuration of the two tridentate (L2)– ligands around the metal centers. Complex 1 contained two lattice methanol molecules whereas 2 were counterbalanced by a nitrate anion beside an uncoordinated water molecule. The crystal structures show a 2-D and 3-D supramolecular architecture due to intermolecular interaction. Electrochemical properties of both complexes were tested by cyclic voltammetry and Electron paramagnetic resonance (EPR) spectroscopy of 2 was also investigated. Fascinatingly, antibacterial efficiencies of all compounds were compared. Furthermore, molecular electrostatic potential (ESP) was computed for both complexes to predict the reaction sites of electrophilic and nucleophilic attacks. Density Functional Theory (DFT) calculations were done to ascertain the optimum geometric configurations. The non-covalent interaction was determined using the Hirshfeld program.