Mono- versus bifunctionalized Schiff base as a condensation product of m-phenylenediamine and salicylaldehyde: experimental and computational studies

A.Z. El-Sonbati et al., in their article "Synthesis, characterization of Schiff base metal complexes and their biological investigation" (Appl. Organometal. Chem. 2019, 33, e5048) reported on the synthesis of a new Schiff base named (E)-2-(((3-aminophenyl)imino)methyl)phenol (also known as N-salicylidene-m-phenylenediamine, HL), which was obtained through condensation reaction of m-phenylenediamine and salicylaldehyde in a 1:1 molar ratio. The reported Schiff base HL was involved in the complexation reaction with a series of metal cations named Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II). Although no crystal structures of either the parent ligand HL or its complexes with the mentioned metal cations were reported, the newly synthesized compounds were characterized by means of elemental analysis, IR-, UV-vis- and 1H NMR spectroscopy, mass-spectrometry, magnetic susceptibility, conductivity and thermal analyses. The antimicrobial activity of the discussed compounds, together with the molecular docking results, were also reported. Additionally, both the Schiff base HL and its metallocomplexes were thoroughly examined by quantum chemical calculations. Despite a plethora of different methods being applied to characterize the obtained compounds, herein, I argue that discussion of the results is doubtful. Furthermore, the results of quantum chemical calculations are dubious and must be reconsidered. Although numerous synthetic attempts failed in this work, the hypothetically possible Schiff base HL was revisited using quantum chemical calculations.