Jahn-Teller Effects in a Vanadate-Stabilized Manganese-Oxo Cubane Water Oxidation Catalyst

We report Jahn–Teller effects in different oxidation states of the water oxidation catalyst [(Mn4O4)(V4O13)(OAc)3]n- and its activated form [(Mn4O4)(V4O13)(OAc)2(H2O)(OH)]n-. Based on all combinatorially possible Jahn–Teller axis arrangements of the Mn(III) atoms, the energetically stable minima are identified. We also derive five heuristic rules that associate a particular energetic cost with certain structural features, like crossings of multiple Jahn–Teller axes, the location of Jahn–Teller axes, or the ligand that is involved in a Jahn–Teller axis. It is found that the different oxidation states seem to localize on different Mn centers, giving rise to clear Jahn–Teller distortions, unlike in previous crystallographic findings where an apparent valence delocalization was found. We conclude that the combination of cubane-vanadate bonds that are chemically inert, cubane-acetate/water bonds that can be activated through a Jahn–Teller axis, and low activation barriers for intramolecular rearrangement of the Jahn–Teller axes plays an important role in the reactivity of this and related compounds.