New 3,4-diaminobenzoic acid Schiff base compounds and their complexes: Synthesis, characterization and thermodynamics

•Schiff base ligands of 3,4-diaminobenzoic acid derivaties (L) have been synthesized and characterized.•The their metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) were prepared.•The formation constants are increased according to the sequence: Cu2+ > Ni2+ > Co2+ > Zn2+.

Some new tetradentate Schiff base ligands (H3L) were prepared via condensation of 3,4-diaminobenzoic acid with 2-hydroxybenzaldehyde derivatives, such as 3,4-bis((E)-2,4-dihydroxybenzylideneamino)benzoic acid (H3L1), 3,4-bis((E)-2-hydroxy-3-methoxybenzylideneamino)benzoic acid (H3L2) and 3,4-bis((E)-5-bromo-2-hydroxybenzylideneamino)benzoic acid (H3L4). Additionally, a tetradentate Schiff base ligand 3,4-bis((E)-2-hydroxybenzylideneamino)benzoic acid (H3L3) and its complexes were synthesized. Their metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) were prepared in good yields from the reaction of the ligands with the corresponding metal acetate. They were characterized based on IR, 1H NMR, Mass spectroscopy and UV–Vis spectroscopy. Also, the formation constants of the complexes were measured by UV–Vis spectroscopic titration at constant ionic strength 0.1 M (NaClO4), at 25 °C in dimethylformamide (DMF) as a solvent.

Graphical abstractSome new tetradentate Schiff base ligands (L) and their metal complexes were prepared via condensation of 3,4-diaminobenzoic acid with 2-hydroxybenzaldehyde derivatives, Khosro Mohammadi, Mahmood Niad and Tahereh JahfariFigure optionsDownload full-size imageDownload as PowerPoint slide