Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH- Addition

Paul F. Smith, Liam Hunt, Anders B. Laursen, Viral Sagar, Shivam Kaushik, Karin U D Calvinho, Gabriele Marotta, Edoardo Mosconi, Filippo De Angelis, G Charles Dismukes

Research output: Contribution to journalArticle

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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 Co2+ or Co3O4 side products. Mass spectrometry of the reaction between isotopically labeled 16O(bridging-oxo) 1A+ and 18O-bicarbonate/water shows (1) no exchange of 18O into the bridging oxos of 1A+, and (2) 36O2 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 1B3+ 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.

Original languageEnglish
Pages (from-to)15460-15468
Number of pages9
JournalJournal of the American Chemical Society
Volume137
Issue number49
DOIs
Publication statusPublished - Dec 16 2015

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Oxidation
Water
Gems
Stereochemistry
Bicarbonates
Cobalt
Reaction products
Discrete Fourier transforms
Stoichiometry
Nuclear magnetic resonance spectroscopy
Mass spectrometry
Paramagnetic resonance
hydroxide ion
Mass Spectrometry
Magnetic Resonance Spectroscopy
Catalysts
Molecules
perchlorate

ASJC Scopus subject areas

  • Chemistry(all)
  • Catalysis
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Smith, P. F., Hunt, L., Laursen, A. B., Sagar, V., Kaushik, S., Calvinho, K. U. D., ... Dismukes, G. C. (2015). Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH- Addition. Journal of the American Chemical Society, 137(49), 15460-15468. https://doi.org/10.1021/jacs.5b09152

Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH- Addition. / Smith, Paul F.; Hunt, Liam; Laursen, Anders B.; Sagar, Viral; Kaushik, Shivam; Calvinho, Karin U D; Marotta, Gabriele; Mosconi, Edoardo; De Angelis, Filippo; Dismukes, G Charles.

In: Journal of the American Chemical Society, Vol. 137, No. 49, 16.12.2015, p. 15460-15468.

Research output: Contribution to journalArticle

Smith, PF, Hunt, L, Laursen, AB, Sagar, V, Kaushik, S, Calvinho, KUD, Marotta, G, Mosconi, E, De Angelis, F & Dismukes, GC 2015, 'Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH- Addition', Journal of the American Chemical Society, vol. 137, no. 49, pp. 15460-15468. https://doi.org/10.1021/jacs.5b09152
Smith PF, Hunt L, Laursen AB, Sagar V, Kaushik S, Calvinho KUD et al. Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH- Addition. Journal of the American Chemical Society. 2015 Dec 16;137(49):15460-15468. https://doi.org/10.1021/jacs.5b09152
Smith, Paul F. ; Hunt, Liam ; Laursen, Anders B. ; Sagar, Viral ; Kaushik, Shivam ; Calvinho, Karin U D ; Marotta, Gabriele ; Mosconi, Edoardo ; De Angelis, Filippo ; Dismukes, G Charles. / Water Oxidation by the [Co4O4(OAc)4(py)4]+ Cubium is Initiated by OH- Addition. In: Journal of the American Chemical Society. 2015 ; Vol. 137, No. 49. pp. 15460-15468.
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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 Co2+ or Co3O4 side products. Mass spectrometry of the reaction between isotopically labeled 16O(bridging-oxo) 1A+ and 18O-bicarbonate/water shows (1) no exchange of 18O into the bridging oxos of 1A+, and (2) 36O2 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 1B3+ 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.",
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