Natural and Artificial Mn₄Ca Cluster for the Water Splitting Reaction

Abstract

The oxygen‐evolving center (OEC) in photosystem II (PSII) is a unique biological catalyst that splits water into electrons, protons, and O2 by using solar energy. Recent crystallographic studies have revealed that the structure of the OEC is an asymmetric Mn4Ca cluster, which provides a blueprint to develop man‐made water‐splitting catalysts for artificial photosynthesis. Although it is a great challenge to mimic the whole structure and function of the OEC in the laboratory, significant advances have recently been achieved. In this Minireview, recent progress on mimicking the natural OEC is discussed. New strategies are suggested to construct more stable and efficient new generation of catalytic materials for the water splitting reaction based on the artificial Mn4Ca cluster in the future.

Artificial photosynthesis: opportunities and challenges of molecular catalysts

“…208 209 Mn complexes have also been designed and synthesized to mimic the electron transfer reactions in PSII and the structures of the OEC. 210,211 Groups of the Swedish Consortium for Artificial Photosynthesis (CAP) did some pioneering research and have prepared several Mn complexes covalently coupled to [Ru(bpy) 3 ] 2+ -type chromophores as functional models of PSII to investigate photoinduced electron transfer of binuclear Ru-Mn assemblies. [212][213][214][215] For example, complex 36 (also named as Licheng-37 synthesized by professor Sun in CAP) showed excellent photoinduced redox properties because it could transfer three electrons from the Mn centers via the Ru photosensitizer to the acceptor, resulting in a Mn III Mn IV state with accumulation of three charges.…”

“…214 The studies on mimicking the key structural motif of the Mn 4 CaO 5 cluster have yielded fruitful results in recent years. 211 The Dismukes group synthesized the first example the Mn 4 O 4 cubane core (complex 37).…”

Mimicking the Catalytic Center for the Water-Splitting Reaction in Photosystem II

“…A remarkable catalytic current was observed during the CV measurement in the presence of an artificial Mn 4 CaO 4 -complex and 1% water in acetonitrile [118] ( Figure 12). The artificial Mn 4 CaO 4 -complexes can also catalyze an oxygen-evolving reaction efficiently by using (CH 3 ) 3 COOH (tert-butyl hydroperoxide) as an oxidant in acetonitrile [130]. However, it should be pointed out that the artificial complex is very sensitive to the experimental conditions.…”

Artificial Mn4Ca Clusters with Exchangeable Solvent Molecules Mimicking the Oxygen‐Evolving Center in Photosynthesis

“…[6] However, this complex has been found to be very unstable in polar solvent, making functional investigation very difficult. [7] Therefore, it is crucial to achieve a robust artificial Mn 4 CaO 4 cluster for the precise mimicking of both structure and function of the OEC in the field of artificial photosynthesis.…”