Solid-State ⁵⁵Mn NMR Spectroscopy of Bis(μ-oxo)dimanganese(IV) [Mn₂O₂(salpn)₂], a Model for the Oxygen Evolving Complex in Photosystem II

We have examined the antiferromagneticly coupled bis(μ-oxo)dimanganese(IV) complex [Mn₂O₂(salpn)₂] (1) with ⁵⁵Mn solid-state NMR at cryogenic temperatures and first-principle theory. The extracted values of the ⁵⁵Mn quadrupole coupling constant, C_Q, and its asymmetry parameter, η_Q, for 1 are 24.7 MHz and 0.43, respectively. Further, there was a large anisotropic contribution to the shielding of each Mn⁴⁺, i.e. a Δσ of 3375 ppm. Utilizing broken symmetry density functional theory, the predicted values of the electric field gradient (EFG) or equivalently the C_Q and η_Q at ZORA, PBE QZ4P all electron level of theory are 23.4 MHz and 0.68, respectively, in good agreement with experimental observations.