A tetranuclear manganese oxo complex with terminal and bridging trifluoroacetate ligands: synthesis and structure of [Mn4O2(O2CCF3)8(bpy)2]

Efforts to prepare tetranuclear manganese oxo complexes that model the water oxidizing center in Photosystem II have focused largely on using unsubstituted acetate and benzoate ligands. We report the reaction of Mn(O2CCF3)2, (n-Bu4N)[MnO4], and bipyridine in trifluoroacetic acid yields the compound [Mn4O2(O2CCF3)8(bpy)2]. X-ray crystallographic studies of this complex show a non-planar {Mn4O2}8+ center with an arrangement of bipyridine and bridging trifluoroacetate ligands that is very similar to the acetate complex [Mn4O2(O2CCH3)7(bpy)2]+ [Christou, et al. J. Am Chem. Soc. 11 (1989) 2086]. The structure differs, however, in that the coordination sites occupied previously by a bridging bidentate acetate ligand are occupied by two terminal monodentate trifluoroacetate ligands in a cis arrangement. One of the terminal trifluoroacetate ligands is hydrogen-bonded to a co-crystallized trifluoroacetic acid molecule.