title: 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.
abstract: We report the syntheses and electrochemical properties of nine new clusters ([LLnMn(IV)3O4(OAc)3(DMF)n](+) (Ln = La(3+), Ce(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), Dy(3+), Yb(3+), and Lu(3+), n = 2 or 3)) supported by a ligand (L(3-)) based on a 1,3,5-triarylbenzene motif appended with alkoxide and pyridine donors. All complexes were obtained by metal substitution of Ca(2+) with lanthanides upon treatment of previously reported LMn3CaO4(OAc)3(THF) with Ln(OTf)3. Structural characterization confirmed that the clusters contain the [LnMn3O4] 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 LMn(IV)3GdO4(OAc)3(DMF)2 cluster with decamethylferrocene, resulted in the formation of LGdMn(IV)2Mn(III)O4(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.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Po-Heng
authors.initials: PH
authors.lastname: Lin
authors.forename: Michael K
authors.initials: MK
authors.lastname: Takase
authors.forename: Theodor
authors.initials: T
authors.lastname: Agapie
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry; D055664:Electrochemical Techniques; D019143:Evolution, Molecular; D005296:Ferrous Compounds / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D001555:Benzene Derivatives; D005296:Ferrous Compounds; D028581:Lanthanoid Series Elements; D009942:Organometallic Compounds; D045332:Photosystem II Protein Complex; D011725:Pyridines; C470210:decamethylferrocenium; D014867:Water; D008345:Manganese; D010100:Oxygen; D002118:Calcium