Versatile coordination behaviour of a multi-dentate Schiff base with manganese(II), copper(II) and zinc(II) ions and their corrosion inhibition study

• Polynuclear Cu(II) and Zn(II) complexes of a Schiff base are prepared.
• Mn(II) forms a quinazoline derivative in methanol but a metal complex in ethanol.
• The monomer unit of Cu(II) complex polymerises via anthranilate-NH2 group.
• Zn(II) complex forms a phenoxo-bridged dimer, which polymerises via –NH2 group.
• The polymeric complexes are better corrosion inhibitors for mild steel than monomer.

A Schiff base, 2-amino-benzoic acid [1-(2-hydroxy-phenyl)-propylidene]-hydrazide (H2abph) and its mononuclear complex [Mn(Habph)2] and one-dimensional coordination polymers [Cu(abph)·DMSO]n and [Zn2(abph)2·2DMSO]n have been synthesised and characterised by various physico-chemical and spectroscopic techniques. The molecular structures of the compounds are also determined by single crystal X-ray crystallography. The reaction of ligand with Cu(II) and Zn(II) in methanol gives polymeric complex, while the similar reaction with Mn(II) results in the formation of a cyclised quinazoline derivative 2,2-dimethyl-3-(1-phenyl-propylideneamino)-2,3-dihydro-1H-quinazolin-4-one. However, the reaction of ligand with Mn(II) in ethanol gives a mononuclear Mn(II) complex. In Mn(II) complex, the ligand coordinates through azomethine-N, carbonyl-O and phenolate-O forming a 6-coordinate distorted octahedral geometry around metal ion. In Cu(II) and Zn(II) complexes, the ligand bonds through azomethine-N, carbonylate-O and phenolate-O. The Cu(II) complex forms a distorted square planar geometry, which polymerises via anthranilate-NH2 group of second unit. The Zn(II) complex exhibits a phenolate-O bridged dimer, which polymerises through anthranilate-NH2 group forming a 5-coordinate distorted square pyramid geometry around each metal ion. The synthesised compounds show an appreciable corrosion inhibition property for mild steel in 1 M HCl medium which varies in the order: H2abph < Mn(II) complex < Cu(II) complex < Zn(II) complex.

Schiff base ligand, 2-amino-benzoic acid [1-(2-hydroxy-phenyl)-propylidene]-hydrazide shows versatile coordination behaviour and results the formation of mono-/polynuclear complexes of Mn(II), Cu(II) and Zn(II). The corrosion-inhibition properties of the compounds have also been evaluated for mild steel in 1 M HCl medium.Figure optionsDownload as PowerPoint slide