The Interaction of Water with Free Mn4 O4 (+) Clusters: Deprotonation and Adsorption-Induced Structural Transformations.

As the biological activation and oxidation of water takes place at an inorganic cluster of the stoichiometry CaMn4 O5 , manganese oxide is one of the materials of choice in the quest for versatile, earth-abundant water splitting catalysts. To probe basic concepts and aid the design of artificial water-splitting molecular catalysts, a hierarchical modeling strategy was employed that explores clusters of increasing complexity, starting from the tetramanganese oxide cluster Mn4 O4 (+) as a molecular model system for catalyzed water activation. First-principles calculations in conjunction with IR spectroscopy provide fundamental insight into the interaction of water with Mn4 O4 (+) , one water molecule at a time. All of the investigated complexes Mn4 O4 (H2 O)n (+) (n=1-7) contain deprotonated water with a maximum of four dissociatively bound water molecules, and they exhibit structural fluxionality upon water adsorption, inducing dimensional and structural transformations of the cluster core.