Synthesizing Mechanism of the Mn 4 Ca Cluster Mimicking the Oxygen-Evolving Center in Photosynthesis.

The photosynthetic oxygen-evolving center (OEC) is a unique Mn 4 CaO 5 cluster that serves as a blueprint to develop superior water-splitting catalysts for the generation of solar fuels in artificial photosynthesis. It is a great challenge and long-standing issue to reveal the synthesizing mechanism of this Mn 4 CaO 5 cluster in both natural and artificial photosynthesis. Herein, efforts were made to reveal the synthesizing mechanism of an artificial Mn 4 CaO 4 cluster, a close mimic of the OEC. Four key intermediates were successfully isolated and structurally characterized for the first time. It was demonstrated that the Mn 4 CaO 4 cluster could be formed through a reaction between a thermodynamically stable Mn 3 CaO 4 cluster and an unusual four-coordinated Mn III ion, followed by stabilization process through binding an organic base (e.g., pyridine) on the "dangling" Mn ion. These findings shed new light on the synthesizing mechanism of the OEC and rational design of new artificial water-splitting catalysts.