The Interaction of Water with Free Mn4O4+ Clusters: Deprotonation and Adsorption-Induced Structural Transformations.

As the biological activation and oxidation of water takes place at an inorganic cluster of the stoichiometry CaMn4O5, 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 Mn4O4+ 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 Mn4O4+, one water molecule at a time. All of the investigated complexes Mn4O4(H2O)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. [ABSTRACT FROM AUTHOR]