Synthesis, Crystal Structure, and Electrochemistry of Iron and Cobalt Complexes Supported by a Pentadentate Amine-bis(phenolate) Ligand

The pentadentate amine-bis(phenolate) ligand 6,6'-(di-pyridin-2-ylmethylazanediyl)bis(methylene)bis(2,4-dimethylphenol) (H2L) was prepared and characterized. This ligand readily coordinates with FeIII or Co-III ions, and the resulting complexes [(FeLCl)-L-III] (1) and [(CoL)-L-III(H2O)]Cl (2) were characterized by elemental analysis. X-ray structural studies show that the ligand in complexes 1 and 2 acts as a pentadentate ligand, leaving one coordination side of the transition metal available for exogenous ligands such as chloride ion (1) or water (2) ligand, and the central metal atoms are hexacoordinate in a similar distorted octahedral arrangement. Electrochemical studies reveal that each of the complexes exhibits multiple redox processes in the potential window investigated. Complex 1 shows one reversible oxidative event at 0.32 V and one quasi-reversible reduction event at -1.03 V, while the complex 2 displays one reversible oxidative event at 0.18 V and one quasi-reversible reduction at -0.64 V.