title: Role of Oxido Incorporation and Ligand Lability in Expanding Redox Accessibility of Structurally Related Mn4Clusters.
abstract: Photosystem II supports four manganese centers through nine oxidation states from manganese(II) during assembly through to the most oxidized state before O2formation and release. The protein-based carboxylate and imidazole ligands allow for significant changes of the coordination environment during the incorporation of hydroxido and oxido ligands upon oxidation of the metal centers. We report the synthesis and characterization of a series of tetramanganese complexes in four of the six oxidation states from MnII3MnIIIto MnIII2MnIV2with the same ligand framework (L) by incorporating four oxido ligands. A 1,3,5-triarylbenzene framework appended with six pyridyl and three alkoxy groups was utilized along with three acetate anions to access tetramanganese complexes, Mn4Ox, withx= 1, 2, 3, and 4. Alongside two previously reported complexes, four new clusters in various states were isolated and characterized by crystallography, and four were observed electrochemically, thus accessing the eight oxidation states from MnII4to MnIIIMnIV3. This structurally related series of compounds was characterized by EXAFS, XANES, EPR, magnetism, and cyclic voltammetry. Similar to the ligands in the active site of the protein, the ancillary ligand (L) is preserved throughout the series and changes its binding mode between the low and high oxido-content clusters. Implications for the rational assembly and properties of high oxidation state metal-oxido clusters are presented.
authors.affiliation: Department of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E. California Blvd MC 127-72, Pasadena CA 91125, USA.
authors.forename: Jacob S
authors.initials: JS
authors.lastname: Kanady
authors.forename: Rosalie
authors.initials: R
authors.lastname: Tran
authors.forename: Jamie A
authors.initials: JA
authors.lastname: Stull
authors.forename: Luo
authors.initials: L
authors.lastname: Lu
authors.forename: Troy A
authors.initials: TA
authors.lastname: Stich
authors.forename: Michael W
authors.initials: MW
authors.lastname: Day
authors.forename: Junko
authors.initials: J
authors.lastname: Yano
authors.forename: R David
authors.initials: RD
authors.lastname: Britt
authors.forename: Theodor
authors.initials: T
authors.lastname: Agapie