Green plants utilize water as a ubiquitous electron source for subsequent CO₂ reduction in light-driven photosynthesis. The oxygen we breathe is formed as a by-product of this water oxidation reaction, which occurs at the so-called oxygen-evolving complex (OEC), an inorganic calcium manganese oxo reaction center located within a large protein assembly known as photosystem II.

Carsten Streb and colleagues, University of Ulm, Germany, have developed a synthetic model for the OEC based on a manganese vanadium oxide polyoxometalate, [Mn₄V₄O₁₇(OAc)₃]^3-. The compound was synthesized using a one-pot reaction of (nBu₄N)₄[V₄O₁₂], Mn(OAc)₃ · 2 H₂O, and (nBu₄N)MnO₄ in acetonitrile. The cluster’s structure and properties were characterized using elemental analysis, cyclovoltammetry, mass spectrometry (MS), and single-crystal X-ray diffraction.

The system allows the stabilization of the reactive manganese-oxo core in several oxidation states. Catalytic studies show that the system is capable of performing the visible-light-driven water-oxidation reaction. The study provides insight into the stabilization of bio-inspired polynuclear metal-oxo reaction sites within polyoxometalate frameworks and provides a basis for understanding the function of homogeneous and heterogeneous metal-oxide water-oxidation catalysts.

• Visible-Light-Driven Water Oxidation by a Molecular Manganese Vanadium Oxide Cluster,
  Benjamin Schwarz, Johannes Forster, McKenna K. Goetz, Duygu Yücel, Claudia Berger, Timo Jacob, Carsten Streb
  Angew. Chem. Int. Ed. 2016.
  DOI: 10.1002/anie.201601799