Synthetic manganese-calcium cluster similar to the catalyst of Photosystem II: Challenges for biomimetic water oxidation

Herein, we report the synthesis, characterization, crystal structure, density functional theory calculations, and water-oxidizing activity of a pivalate Mn-Ca cluster. All of the manganese atoms in the cluster are Mn (IV) ions and have distorted MnO6 octahedral geometry. Three Mn(IV) ions together with a Ca(II), and four-oxido groups form a cubic Mn3CaO4 unit which is similar to the Mn3CaO4 cluster in the water-oxidizing complex of Photosystem II. Using scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, extended X-ray absorption spectroscopy, chronoamperometry, and electrochemical methods, a conversion into man-sized Mn-oxide is observed for the cluster under water-oxidation reaction.