| To mimic the nature oxygen evolving complex (OEC) in photosystem II (PSII), various manganese-containing complexes have been made. In this dissertation, the manganese complexes studied are synthesized by the Agapie's group at the California Institute of Technology and EPR studies are conducted on these compounds.;A synthetic framework with a well-defined ligand set that supports tetranuclear clusters is employed. To mimic the "open" or "closed" form of S2 state of the photosystem II, a series of compounds are synthesized. The "closed" form mimics heterometal-containing manganese cluster [MMn3O4]n+ (M = Y, Zn, Ca, Sr, Sc). The signals are assigned to an S = 9/2 ground state using continuous wave (CW) EPR and pulsed-EPR techniques including electron spin-echo envelope modulation (ESEEM) and phase-inverted echo-amplitude detected nutation (PEANUT) experiments. Increased zero-field splitting with respect to decreasing Lewis acidity of the hetero metal is observed. The "open" form compounds [MMn 3O2]n+ are assigned to an S = 3/2 ground state. Protonation on the oxo bridge between the heterometal and manganese is investigated by variable-temperature experiments. A smaller exchange-coupling is observed upon protonation. The intermediate coupling case is investigated by including the zero-field splitting term in the energy level calculations of the spin system. |
