A Linear Mn₃ Molecular Cluster as a Bifunctional Electrocatalyst for Overall Water Splitting

In this research article, a cluster material [Mn₃L₂(μ₂-OAc)₂] (1) with linear Mn^II···Mn^II···Mn^II motif in which two peripheral Mn centers are five-coordinated and the central Mn center is six-coordinated has been explored as an excellent OER and HER molecular electrocatalyst (H₂L = 2,2'-(propane-1,3-diylbis(azaneylylidene))bis(ethan-1-yl-1-ylidene)diphenol); (OAc═CH₃CO₂^-). The organic framework H₂L is so flexible, and the preference toward linear assembly is so high, that this cluster is readily accomplished by a synthetic approach that uses H₂L and Mn(OAc)₂·4H₂O as the building blocks. Characterizations of 1 have been performed by molar conductance, microanalysis, FTIR, UV-vis, FESEM, TGA, PXRD, and SCXRD analyses. The crystal structure of 1 contains two crystallographically equivalent [Mn^IIL] species interconnected by a central Mn^II ion via the four μ₂-phenoxide and two μ₂-acetate bridges. Measurement of electrical properties of 1 reveals an interesting current-voltage feature of the aluminum/1 two-terminal device structure. Cluster 1 shows outstanding activity when working as both an OER and HER electrocatalyst, with overpotential values of 324 and 130 mV, respectively, at a current density of 10 mA/cm². DFT computational studies reveal mechanistic insight into the OER and HER processes, suggesting that the Mn^II-O_phenoxide-Mn^II linkage is the active site for the formation of molecular oxygen and hydrogen.