Synthesis, characterization and spectroscopic and electrochemical studies of new axially coordinated cobalt(III) salen (salen = N,N′-bis(salicylidene)-1,2-ethylenediamine) complexes. The crystal structure of [CoIII(salen)(aniline)2]ClO4

Cobalt(III) complexes with some salen ligands (salen = N,N′-bis(salicylidene)-1,2-ethylenediamine) as equatorial and potentially tetradentate ligands and with different axial amine ligands (cyclohexylamine, aniline, 4-picoline and pyridine) were synthesized in situ and characterized by IR, 1H NMR and elemental analysis. Electronic spectra and electrochemical properties of the complexes were studied in DMF solutions. Electronic structure calculations indicate that the absorption between 420 and 440 nm, which are the lowest energy transfers in the complexes, are attributed to metal–ligand charge transfer transitions. The cyclic voltammetry of the complexes show an irreversible reduction of Co(III) to Co(II) and a reversible reduction of Co(II) to Co(I). The axial ligands affect reduction potentials of Co(III) in the order of changes of axial ligands’ pKa. The crystal structure of [Co(salen)(aniline)2]ClO4 was determined. In the [Co(salen)(aniline)2]ClO4, cobalt(III) center is six coordinated surrounded by an equatorial tetradentate salen Schiff-base ligand and two aniline axial ligands and ClO4- acts as a counter ion.

Graphical abstractCobalt(III) complexes with some potentially tetradentate salen Schiff-bases as equatorial ligands and with different axial amine ligands were synthesized in situ and characterized by IR, 1H NMR and elemental analysis. Electronic structure calculations indicate metal–ligand charge transfer transitions between 420 and 440 nm. The cyclic voltammetry of the complexes show that the axial amine ligands affect reduction potentials of Co(III) in the order of changes of their pKa. In the crystal structure of [Co(salen)(aniline)2]ClO4 cobalt(III) center is six coordinated surrounded by an equatorial tetradentate salen ligand and two aniline axial ligands and ClO4- acts as a counter ion.Figure optionsDownload full-size imageDownload as PowerPoint slide