Structural similarities in enzymatic, homogeneous and heterogeneous catalysts of water oxidation

A virtually identical cubical or cubane core structure appears to be a key commonality in several active homogeneous, heterogeneous and enzymatic water oxidation catalysts. We show that X-ray crystal structures of the CaMn ₃O₄ core of the water oxidizing complex of Photosystem II coincide remarkably closely with comparable structures in a range of non-biological Co or Mn-based homogeneous and heterogeneous water oxidation catalysts. Included amongst these are molecular Co₄O₄ and Mn₄O₄ cubanes, as well as Co and Mn spinels containing cubical arrangements. This observation supports the existence of an optimum structural element for water oxidation catalysis. It also offers a potential avenue for comparing and relating homogeneous, heterogeneous and enzymatic catalysis to each other.