Redox-Induced Structural Change in Artificial Heterometallic-Oxide Cluster Mimicking the Photosynthetic Oxygen-Evolving Center.

The oxygen-evolving center (OEC) in photosynthesis is a unique Mn 4 CaO 5 -cluster that catalyzes the water-splitting reaction in nature. Understanding its catalytic mechanism for the O=O bond formation is of great challenge and long-standing issue, which is severely restricted by the lack of precise structure and mechanism mimics of this heterometallic-oxide cluster. Herein, we report two synthetic (Mn 3 XO 4 ) 2 O-clusters (X=Sr 2+ , La 3+ ) that closely mimic the heterometallic-oxide Mn 3 XO 4 cubane and three different types of μ-oxide bridges (μ 2 -O 2- , μ 3 -O 2- , and μ 4 -O 2- ) simultaneously as seen in the OEC. By resolving the crystal structures of both oxidized and reduced forms of the cluster, we have identified significant redox-induced structural changes that take place on the μ 2 -oxide bridge, rather than the μ 4 -oxide or μ 3 -oxide bridges. Our results provide chemical insights into understanding the reactivity of three different types of oxide bridges in the biological Mn 4 CaO 5 -cluster in PSII.