Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution

C. André Ohlin, Stephen J. Harley, J. Gregory McAlpin, Rosalie K. Hocking, Brandon Q. Mercado, Rene L. Johnson, Eric Villa, Mary Kate Fidler, Marilyn M. Olmstead, Leone Spiccia, R. David Britt, William H. Casey

Research output: Contribution to journalArticle

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Abstract

Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to Co II atoms in two polyoxotungstate sandwich molecules using the 17O-NMR-based Swift-Connick method. The compounds were the [Co 4(H2O)2(B-α-PW9O 34)2]10- and the larger αββ α-[Co4(H2O)2(P2W 15O56)2]16- ions, each with two water molecules bound trans to one another in a CoII sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal X-ray crystallography, and potentiometry. For [Co4(H2O)2(B-α-PW 9O34)2]10- at pH 5.4, we estimate: k298=1.5(5)±0.3à- 106 s-1, ΔH=39.8±0.4 kJmol-1, ΔS =+7.1±1.2 Jmol-1K-1 and ΔV=5.6 ±1.6 cm3mol-1. For the Wells-Dawson sandwich cluster (αββα-[Co4(H 2O)2(P2W15O56) 2]16-) at pH 5.54, we find: k298=1.6(2) ±0.3à- 106 s-1, ΔH=27. 6±0.4 kJmol-1 ΔS=-33±1.3 Jmol -1K-1 and ΔV=2.2±1.4 cm 3mol-1 at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR spectroscopy as S=3/2 Co II species (such as the [Co(H2O)6]2+ monomer ion) and by the significant reduction of the Co-Co vector in the XAS spectra.

Original languageEnglish
Pages (from-to)4408-4417
Number of pages10
JournalChemistry - A European Journal
Volume17
Issue number16
DOIs
StatePublished - Apr 11 2011
Externally publishedYes

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Cobalt compounds
Ion exchange
Water
Ions
Molecules
Paramagnetic resonance
Ligands
Nuclear magnetic resonance
Extended X ray absorption fine structure spectroscopy
X ray crystallography
Ultraviolet spectroscopy
Solar energy
Monomers
Association reactions
Single crystals
Spectroscopy
Atoms
Oxidation

All Science Journal Classification (ASJC) codes

  • Chemistry(all)

Cite this

Ohlin, C. A., Harley, S. J., McAlpin, J. G., Hocking, R. K., Mercado, B. Q., Johnson, R. L., ... Casey, W. H. (2011). Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution. Chemistry - A European Journal, 17(16), 4408-4417. https://doi.org/10.1002/chem.201003550

Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution. / Ohlin, C. André; Harley, Stephen J.; McAlpin, J. Gregory; Hocking, Rosalie K.; Mercado, Brandon Q.; Johnson, Rene L.; Villa, Eric; Fidler, Mary Kate; Olmstead, Marilyn M.; Spiccia, Leone; Britt, R. David; Casey, William H.

In: Chemistry - A European Journal, Vol. 17, No. 16, 11.04.2011, p. 4408-4417.

Research output: Contribution to journalArticle

Ohlin, CA, Harley, SJ, McAlpin, JG, Hocking, RK, Mercado, BQ, Johnson, RL, Villa, E, Fidler, MK, Olmstead, MM, Spiccia, L, Britt, RD & Casey, WH 2011, 'Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution', Chemistry - A European Journal, vol. 17, no. 16, pp. 4408-4417. https://doi.org/10.1002/chem.201003550
Ohlin CA, Harley SJ, McAlpin JG, Hocking RK, Mercado BQ, Johnson RL et al. Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution. Chemistry - A European Journal. 2011 Apr 11;17(16):4408-4417. https://doi.org/10.1002/chem.201003550
Ohlin, C. André ; Harley, Stephen J. ; McAlpin, J. Gregory ; Hocking, Rosalie K. ; Mercado, Brandon Q. ; Johnson, Rene L. ; Villa, Eric ; Fidler, Mary Kate ; Olmstead, Marilyn M. ; Spiccia, Leone ; Britt, R. David ; Casey, William H. / Rates of water exchange for two cobalt(II) heteropolyoxotungstate compounds in aqueous solution. In: Chemistry - A European Journal. 2011 ; Vol. 17, No. 16. pp. 4408-4417.
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AU - Ohlin, C. André

AU - Harley, Stephen J.

AU - McAlpin, J. Gregory

AU - Hocking, Rosalie K.

AU - Mercado, Brandon Q.

AU - Johnson, Rene L.

AU - Villa, Eric

AU - Fidler, Mary Kate

AU - Olmstead, Marilyn M.

AU - Spiccia, Leone

AU - Britt, R. David

AU - Casey, William H.

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N2 - Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to Co II atoms in two polyoxotungstate sandwich molecules using the 17O-NMR-based Swift-Connick method. The compounds were the [Co 4(H2O)2(B-α-PW9O 34)2]10- and the larger αββ α-[Co4(H2O)2(P2W 15O56)2]16- ions, each with two water molecules bound trans to one another in a CoII sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal X-ray crystallography, and potentiometry. For [Co4(H2O)2(B-α-PW 9O34)2]10- at pH 5.4, we estimate: k298=1.5(5)±0.3à- 106 s-1, ΔH≠=39.8±0.4 kJmol-1, ΔS ≠=+7.1±1.2 Jmol-1K-1 and ΔV≠=5.6 ±1.6 cm3mol-1. For the Wells-Dawson sandwich cluster (αββα-[Co4(H 2O)2(P2W15O56) 2]16-) at pH 5.54, we find: k298=1.6(2) ±0.3à- 106 s-1, ΔH≠=27. 6±0.4 kJmol-1 ΔS≠=-33±1.3 Jmol -1K-1 and ΔV≠=2.2±1.4 cm 3mol-1 at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR spectroscopy as S=3/2 Co II species (such as the [Co(H2O)6]2+ monomer ion) and by the significant reduction of the Co-Co vector in the XAS spectra.

AB - Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to Co II atoms in two polyoxotungstate sandwich molecules using the 17O-NMR-based Swift-Connick method. The compounds were the [Co 4(H2O)2(B-α-PW9O 34)2]10- and the larger αββ α-[Co4(H2O)2(P2W 15O56)2]16- ions, each with two water molecules bound trans to one another in a CoII sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal X-ray crystallography, and potentiometry. For [Co4(H2O)2(B-α-PW 9O34)2]10- at pH 5.4, we estimate: k298=1.5(5)±0.3à- 106 s-1, ΔH≠=39.8±0.4 kJmol-1, ΔS ≠=+7.1±1.2 Jmol-1K-1 and ΔV≠=5.6 ±1.6 cm3mol-1. For the Wells-Dawson sandwich cluster (αββα-[Co4(H 2O)2(P2W15O56) 2]16-) at pH 5.54, we find: k298=1.6(2) ±0.3à- 106 s-1, ΔH≠=27. 6±0.4 kJmol-1 ΔS≠=-33±1.3 Jmol -1K-1 and ΔV≠=2.2±1.4 cm 3mol-1 at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR spectroscopy as S=3/2 Co II species (such as the [Co(H2O)6]2+ monomer ion) and by the significant reduction of the Co-Co vector in the XAS spectra.

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