Dimensionality dependent water splitting mechanisms on free manganese oxide clusters.

The interaction of ligand-free manganese oxide nanoclusters with water is investigated, aiming at uncovering phenomena which could aid the design of artificial water-splitting molecular catalysts. Gas phase measurements in an ion trap in conjunction with first-principles calculations provide new mechanistic insight into the water splitting process mediated by bi- and tetra-nuclear singly charged manganese oxide clusters, Mn2O2(+) and Mn4O4(+). In particular, a water-induced dimensionality change of Mn4O4(+) is predicted, entailing transformation from a two-dimensional ring-like ground state structure of the bare cluster to a cuboidal octa-hydroxy-complex for the hydrated one. It is further predicted that the water splitting process is facilitated by the cluster dimensionality crossover. The vibrational spectra calculated for species occurring along the predicted pathways of the reaction of Mn4O4(+) with water provide the impetus for future explorations, including vibrational spectroscopic experiments.