title: Water Oxidation by the [Co4O4(OAc)4(py)4](+) Cubium is Initiated by OH(-) Addition.
abstract: The cobalt cubium Co4O4(OAc)4(py)4(ClO4) (1A(+)) containing the mixed valence [Co4O4](5+) core is shown by multiple spectroscopic methods to react with hydroxide (OH(-)) but not with water molecules to produce O2. The yield of reaction products is stoichiometric (>99.5%): 41A(+) + 4OH(-) → O2 + 2H2O + 41A. By contrast, the structurally homologous cubium Co4O4(trans-OAc)2(bpy)4(ClO4)3, 1B(ClO4)3, produces no O2. EPR/NMR spectroscopies show clean conversion to cubane 1A during O2 evolution with no Co(2+) or Co3O4 side products. Mass spectrometry of the reaction between isotopically labeled μ-(16)O(bridging-oxo) 1A(+) and (18)O-bicarbonate/water shows (1) no exchange of (18)O into the bridging oxos of 1A(+), and (2) (36)O2 is the major product, thus requiring two OH(-) in the reactive intermediate. DFT calculations of solvated intermediates suggest that addition of two OH(-) to 1A(+) via OH(-) insertion into Co-OAc bonds is energetically favored, followed by outer-sphere oxidation to intermediate [1A(OH)2](0). The absence of O2 production by cubium 1B(3+) indicates the reactive intermediate derived from 1A(+) requires gem-1,1-dihydoxo stereochemistry to perform O-O bond formation. Outer-sphere oxidation of this intermediate by 2 equiv of 1A(+) accounts for the final stoichiometry. Collectively, these results and recent literature (Faraday Discuss., doi:10.1039/C5FD00076A and J. Am. Chem. Soc. 2015, 137, 12865-12872) validate the [Co4O4](4+/5+) cubane core as an intrinsic catalyst for oxidation of hydroxide by an inner-sphere mechanism.
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Paul F
authors.initials: PF
authors.lastname: Smith
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Liam
authors.initials: L
authors.lastname: Hunt
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Anders B
authors.initials: AB
authors.lastname: Laursen
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Viral
authors.initials: V
authors.lastname: Sagar
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Shivam
authors.initials: S
authors.lastname: Kaushik
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: Karin U D
authors.initials: KU
authors.lastname: Calvinho
authors.affiliation: Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR) , Via Elce di Sotto 8, Perugia 06123, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Marotta
authors.affiliation: Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR) , Via Elce di Sotto 8, Perugia 06123, Italy.
authors.forename: Edoardo
authors.initials: E
authors.lastname: Mosconi
authors.affiliation: Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), Istituto CNR di Scienze e Tecnologie Molecolari (ISTM-CNR) , Via Elce di Sotto 8, Perugia 06123, Italy.
authors.forename: Filippo
authors.initials: F
authors.lastname: De Angelis
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, the State University of New Jersey , 610 Taylor Road, Piscataway, New Jersey 08854, United States.
authors.forename: G Charles
authors.initials: GC
authors.lastname: Dismukes