title: Speciation of the catalytic oxygen evolution system: [MnIII/IV2(mu-O)2(terpy)2(H2O)2](NO3)3 + HSO5-.
abstract: [MnIII/IV2(-O)2(terpy)2(OH2)2](NO3)3 (1, where terpy = 2,2':6'2' '-terpyridine) + oxone (2KHSO5 x KHSO4 x K2SO4) provides a functional model system for the oxygen-evolving complex of photosystem II that is based on a structurally relevant Mn-(-O)2-Mn moiety (Limburg, J.; et al. J. Am. Chem. Soc. 2001, 123, 423-430). In this study, electron paramagnetic resonance, ultraviolet-visible spectroscopy, electrospray ionization mass spectrometry, X-ray absorption spectroscopy, and gas-phase stable isotope ratio mass spectrometry were utilized to identify the title compounds in the catalytic solution. We find that (a) O2 evolution does not proceed through heterogeneous catalysis by MnO2 or other decomposition products, that (b) O atoms from solvent water are incorporated into the evolved O2 to a significant extent but not into oxone, that (c) the MnIII/IV2 title compound 1 is an active precatalyst in the catalytic cycle of O2 evolution with oxone, while the MnIV/IV2 oxidation state is not, and that (d) the isotope label incorporation in the evolved O2, together with points a-c above, is consistent with a mechanism involving competing reactions of oxone and water with a "MnV=O" intermediate in the O-O bond-forming step.
authors.affiliation: Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Hongyu
authors.initials: H
authors.lastname: Chen
authors.forename: Ranitendranath
authors.initials: R
authors.lastname: Tagore
authors.forename: Gerard
authors.initials: G
authors.lastname: Olack
authors.forename: John S
authors.initials: JS
authors.lastname: Vrettos
authors.forename: Tsu-Chien
authors.initials: TC
authors.lastname: Weng
authors.forename: James
authors.initials: J
authors.lastname: Penner-Hahn
authors.forename: Robert H
authors.initials: RH
authors.lastname: Crabtree
authors.forename: Gary W
authors.initials: GW
authors.lastname: Brudvig
mesh_terms: D002384:Catalysis; D008345:Manganese / Q000737:chemistry* / Q000378:metabolism; D008954:Models, Biological; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010126:Ozone / Q000737:chemistry; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism
chemical_list: D009942:Organometallic Compounds; D045332:Photosystem II Protein Complex; D008345:Manganese; D010126:Ozone; D010100:Oxygen