Can oxidation states and the protonation pattern of oxomanganese complexes be recognized from their structures?

Abstract

Multi-core oxomanganese complexes can adopt different oxidation states and protonation patterns depending on ligands and external conditions (for example, solvent, pH, and redox potential). An archetypical example of such complexes is the Mn₄Ca cluster in the oxygen-evolving complex (OEC) of photosystem II (PSII). Despite the recent high-resolution crystal structure of PSII, some uncertainty about the oxidation state of the Mn centers and the protonation pattern of the oxygen atoms bridging the metals still exists. In this work, we construct a quantum-chemically based tool to “recognize” the oxidation state and the protonation pattern of oxomanganese complexes from their experimental structure. Combined with simple structural information, our tool can be employed as an empirical guideline to recognize the oxidation state and/or the protonation pattern of those oxomanganese complexes for which this information is not experimentally available.