Fig. 5.
Top: DFT-optimized structures of the Mn4O5Ca cluster in the S2 state (distances given in Ångström). Note that the “closed cubane” (left) and “open cubane” (right) structures have almost the same energy but different positions of the MnIII ion (Mn4 vs. Mn1, respectively) and different total (effective) spin ground states. This explains the two EPR signals observed for this state (shown below as first derivative X-band EPR spectra), with g = 4.1 (Seff = 5/2; no hyperfine structure) and g = 2 (Seff = ½; multiline signal). The bottom trace shows simulations of the two EPR absorption signals.
Figure modified from (Krewald et al. 2016; Pantazis et al. 2012)