Tetranuclear Co^II₄O₄ Cubane Complex: Effective Catalyst Toward Electrochemical Water Oxidation

Area of Science:

• Coordination Chemistry
• Materials Science
• Electrochemistry

Background:

• Multisite coordination ligands are crucial for developing advanced metal complexes.
• Cobalt complexes are actively researched for catalytic applications, including oxygen evolution reactions.

Purpose of the Study:

• To synthesize and characterize a novel tetranuclear cobalt complex.
• To investigate the electrochemical properties of the complex for oxygen evolution reactions (OER).

Main Methods:

• Synthesis of the tetranuclear cobalt complex (1) using Co(OAc)2·6H2O and a diphenol-based ligand.
• X-ray diffraction for structural elucidation of the Co4O4 cubane core and coordination geometry.
• Magnetic susceptibility measurements to analyze magnetic coupling and anisotropy.
• Electrochemical techniques (cyclic voltammetry, chronoamperometry) to evaluate OER performance.
• Electrochemical impedance spectroscopy (EIS) to study charge transfer kinetics.

Main Results:

• Formation of a tetranuclear cobalt complex, Co4(L)2(μ-η1:η1-OAc)2(η2-OAc)2]·1.5CH3OH·1.5CHCl3 (1), with a distorted Co4O4 cubane core.
• Identification of two distinct CoII centers with distorted octahedral and pentagonal-bipyramidal geometries.
• Predominant antiferromagnetic coupling (J = -2.1 cm−1) and easy-plane magnetic anisotropy.
• Demonstration of electrochemical OER with a low overpotential (325 mV) and Tafel slope (85 mV dec−1).
• Lower charge transfer resistance (2.927 Ω) compared to Co3O4 (5.242 Ω), indicating enhanced catalytic activity.

Conclusions:

• The synthesized tetranuclear cobalt complex exhibits unique structural and magnetic properties.
• Complex 1 is a promising electrocatalyst for the oxygen evolution reaction (OER) under alkaline conditions.
• The complex's enhanced catalytic activity is attributed to its rapid charge transfer kinetics.