Synthesis, structure and electrochemistry of Co(III) complexes with an unsymmetrical Schiff base ligand derived from 2-aminobenzylamine and pyrrole-2-carboxaldehyde

A series of cobalt(III) complexes with a new unsymmetrical tetradentate Schiff base ligand N,N’-bis(pyrrol-2-ylmethylene)-2-aminobenzylamine, H2pyrabza, formed by the condensation of 2-pyrrole carboxaldehyde and 2-aminobenzylamine, has been synthesized and characterized by elemental analyses, IR, UV–Vis and 1H NMR spectroscopy. These complexes have the general formula trans-[CoIII(L)(amine)2]X {L2− = pyrabza, and amine = N-methylimidazole (N-MeIm) (1), 3-methylpyridine (3-Mepy) (2), 4-methylpyridine (4-Mepy) (3), pyridine (py) (4), X = BPh4-}. The structure of compound 1 has been determined by X-ray crystallography. The geometry around the central cobalt ion is distorted octahedral. The electrochemical behavior of these complexes was also investigated. The reduction potential of Co(III), ranging from −0.79 V for 1 to −0.44 V for 4, shows a relatively good correlation with the σ-donor ability of the axial ligands.

A series of cobalt(III) complexes with a new unsymmetrical tetradentate Schiff base ligand, H2pyrabza, formed by the condensation of 2-pyrrole carboxaldehyde and 2-aminobenzylamine, has been synthesized and characterized. The X-ray crystal structure of trans-[CoIII(pyrabza)(N-MeIm)2]BPh4 has been determined. Spectral and electrochemical studies are also reported.Figure optionsDownload as PowerPoint slideHighlights
► A new unsymmetrical Schiff base, H2pyrabza, has been synthesized and characterized.
► Four new trans-[CoIII(pyrabza)(amine)2]BPh4 complexes have been prepared.
► The X-ray structure of trans-[CoIII(pyrabza)(N-MeIm)2]BPh4 has been determined.
► Spectroscopic and electrochemical properties of these complexes have been studied.
► CoII/I process becomes quasi-reversible by narrowing the scanning potential window.