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, CQ, and its asymmetry parameter, ηQ, 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 CQ and ηQ at ZORA, PBE QZ4P all electron level of theory are 23.4 MHz and 0.68, respectively, in good agreement with experimental observations.