Investigations of the Effect of the Non-Manganese Metal in Heterometallic-Oxido Cluster Models of the Oxygen Evolving Complex of Photosystem II: Lanthanides as Substitutes for Calcium

We report the syntheses and electrochemical properties of nine new clusters ([LLnMnIV(3)O(4)(OAc)(3)(DMF)n(])(+) (Ln = La3+, Ce3+, Nd3+, Eu3+, Gd3+, Tb3+, Dy3+, Yb3+, and Lu3+, n = 2 or 3)) supported by a ligand (L3-) based on a 1,3,5-triarylbenzene motif appended with alkoxide and pyridine donors. All complexes were obtained by metal substitution of Ca2+ with lanthanides upon treatment of previously reported LMn3CaO4(OAc)(3)(THF) with Ln(OTf)(3). Structural characterization confirmed that the clusters contain the [LnMn(3)O(4)] cubane motif. The effect of the redox-inactive centers on the electronic properties of the Mn3O4 cores was investigated by cyclic voltammetry. A linear correlation between the redox potential of the cluster and the ionic radii or pKa of the lanthanide metal ion was observed. Chemical reduction of the (LMn3GdO4)-Gd-IV(OAc)(3)(DMF)(2) cluster with decamethylferrocene, resulted in the formation of (LGdMn2MnO4)-Mn-IV-O-III(OAc)(3)(DMF)(2), a rare example of mixed-valence [MMn3O4] cubane. The lanthanide-coordinated ligands can be substituted with other donors, including water, the biological substrate.