Conclusions The data presented in this paper show that the S2 state EPR signals from the OEC arise from the interaction of more than one paramagnetic site. However, our temperature dependence data cannot be accounted for by a simple Mn dimer model, unless such a dimer arises from a ferromagnetic exchange coupling of low-spin forms of Mn. As noted above, low-spin Mn complexes are rare and not likely to be present in the OEC. A ...
