Electrocatalytic water oxidation studies of a tetranuclear Cu(ii) complex with cubane-like core Cu4(μ3-O)4

Abstract

To mimic the strategy used by natural photosynthesis in Photosystem II, which adopts the cubic Mn₄CaO₅ cluster as a natural oxygen-evolving complex, a bio-inspired cubane-like tetranuclear cluster [Cu₄(pdmH)₄(OAc)₂](NO₃)₂·3H₂O (1) has been synthesized successfully with pyridine-2, 6-dimethanol as the ideal ligand, and investigated by X-ray crystallography, PXRD, in situ UV-vis-NIR spectroelectrochemical analysis, and magneto- and electrochemistry. By X-ray analysis, it is shown that the distorted cubane-like core Cu₄(μ₃-O)₄ is composed of four Cu^II and four μ₃-O which arrange at the vertices of a slightly distorted cube. Electrochemical studies indicate that complex 1 presents potential properties as an effective molecular catalyst for electrocatalytic water oxidation under aqueous alkaline conditions at a potential of ∼1.20 V vs. NHE with a relatively low overpotential of ∼400–665 mV vs. NHE, which may result from the unique covalent metal–oxo bonding. Magnetic susceptibility measurements reveal that complex 1 displays overall antiferromagnetic exchanges between the Cu(II) ions within the clusters. Temperature dependence of in-phase (χ_M′) ac susceptibility signals display frequency-dependence, whereas the out-of-phase (χ_M′′) signals show no significant frequency-dependence for complex 1, which indicates that the complex may not be a SMM.