The Possible Mn Hyperfine Interactions and Oxidation States of the Manganese Cluster in OEC Using Multiline Signal (MLS) Simulation Data with Average of Weighted Computations

Abstract

Understanding the structure of oxygen evolving complex (OEC) fully still remains a challenge. Lately computational chemistry with the data from more detailed X-ray diffraction (XRD) OEC structure, has been used extensively in exploring the mechanisms of water oxidation in the OEC. The present study involves simulation studies of the X-band continuous wave electron-magnetic resonance (CW-EPR) generated S2 state signals, to investigate whether the data is in agreement with the four manganese ions in the OEC, being organised as a ‘3+1’ model or ‘dimer of dimers’ model. The question that still remains is how much does each Mn ion contribute to the “g2multiline” signal through its hyperfine interactions in OEC? This is revealed in part by the structure of multiline signal studied in this project. The method of data analysis involves numerical simulations of the experimental spectra on relevant models of the OEC cluster. The simulations of the X-band CW-EPR multiline spectra, revealed three manganese ions having hyperfine couplings with large anisotropy. These are most likely MnIII centres and these clearly support the ‘low’ oxidation state OEC paradigm model, with a mean oxidation of 3.25 in the S2 state. This is consistent with the earlier data, but the present results clearly indicate that heterogeneity in hyperfine couplings exist in samples as typically prepared.