Synthesis and structure of linear hexanuclear manganese (II) benzoate cluster

From a reaction system including benzoic acid and Mn(NO3)(2) in alkali medi um, two hexanuclear manganese benzoate cluster compounds have been synthesi zed. A compound [Et4N](2)[Mn-6(PhCOO)(14)] has been structurally characteri zed, which contains hexanuclear Mn-II moieties extending unlimitedly to for m one-dimensional linear structure. Carboxyl oxygen atoms are bridged in va riety of modes to the Mn atoms, forming an arrangement like a sinusoid for the Mn atoms. The structural parameters of these compounds were compared wi th the data obtained from EXAFS determination for the Mn cluster in the OEC of PSII, supporting that the coordination sphere of the Mn site in the OEC may contain carboxyl bridges. The possible combination modes between the c arboxyl group and the Mn atoms have been suggested. The NMR signals exhibit widening and shift produced by the influence of the paramagnetic Mn-II sit es. The red-shift of the absorption in IR spectrum was observed to be attri buted to the coordination of the carboxyl group to the Mn atom, supporting the result of the study on crystal structure.