Metal-Centered Redox Activity in a Polymeric Cobalt(II) Complex of a Sterically Hindered Salen Type Ligand

Abstract This paper reports on the peculiarities of the metal-centered redox activity in a polymeric cobalt(II) complex of a sterically hindered tetradentate N2O2 Schiff base (salen type) ligand. A Co(III)/Co(II) redox process in the polymer film during its formation on the electrode and subsequent electrochemical switching in a monomer-free electrolyte has been characterized by cyclic voltammetry, electrochemical quartz crystal microbalance, and electrochemical impedance spectroscopy. The obtained results indicate that cobalt ions in the polymer can effectively function as independent redox sites. The metal-centered redox activity largely governed by the unique features of a sterically hindered salen type ligand is time-dependent and sensitive to the presence of coordinating species in the electrolyte. In relatively fast potentiodynamic scans, the Co(III)/Co(II) redox switching in an acetonitrile solution exhibits a high degree of chemical and electrochemical reversibility and stability and can be considered as a quasi-equilibrium process. A novel analytical solution for modeling quasi-equilibrium voltammetric curves accounting for the existence of short-range interactions within redox polymer films is proposed and used to estimate the attraction constant in the cobalt-salen type polymer. The study findings contribute to a better understanding of the prospects of using electrodes modified with the investigated polymeric complex in energy storage and catalytic applications.