Tetranuclear Co II 4 O 4 Cubane Complex: Effective Catalyst Toward Electrochemical Water Oxidation.

The reaction of Co(OAc) 2 ·6H 2 O with 2,2'-[{(1 E ,1' E )-pyridine-2,6-diyl-bis(methaneylylidene)bis(azaneylylidene)}diphenol](LH 2 ) a multisite coordination ligand and Et 3 N in a 1:2:3 stoichiometric ratio forms a tetranuclear complex Co 4 (L) 2 (μ-η 1 :η 1 -OAc) 2 (η 2 -OAc) 2 ]· 1.5 CH 3 OH· 1.5 CHCl 3 ( 1 ). Based on X-ray diffraction investigations, complex 1 comprises a distorted Co 4 O 4 cubane core consisting of two completely deprotonated ligands [L] 2- and four acetate ligands. Two distinct types of Co II centers exist in the complex, where the Co(2) center has a distorted octahedral geometry; alternatively, Co(1) has a distorted pentagonal-bipyramidal geometry. Analysis of magnetic data in 1 shows predominant antiferromagnetic coupling ( J = -2.1 cm -1 ), while the magnetic anisotropy is the easy-plane type ( D 1 = 8.8, D 2 = 0.76 cm -1 ). Furthermore, complex 1 demonstrates an electrochemical oxygen evolution reaction (OER) with an overpotential of 325 mV and Tafel slope of 85 mV dec -1 , required to attain a current density of 10 mA cm -2 and moderate stability under alkaline conditions (pH = 14). Electrochemical impedance spectroscopy studies reveal that compound 1 has a charge transfer resistance ( R ct ) of 2.927 Ω, which is comparatively lower than standard Co 3 O 4 (5.242 Ω), indicating rapid charge transfer kinetics between electrode and electrolyte solution that enhances higher catalytic activity toward OER kinetics.