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Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between quaric acid and 4,4?-bipyridine

Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between quaric acid and 4,4?-bipyridine
Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between quaric acid and 4,4?-bipyridine
We have applied a combination of spectroscopic and diffraction methods to study the adduct formed between squaric acid and bypridine, which has been postulated to exhibit proton transfer associated with a single-crystal to single-crystal phase transition at ca. 450 K. A combination of X-ray single-crystal and very-high flux powder neutron diffraction data confirmed that a proton does transfer from the acid to the base in the high-temperature form. Powder X-ray diffraction measurements demonstrated that the transition was reversible but that a significant kinetic energy barrier must be overcome to revert to the original structure. Computational modeling is consistent with these results. Modeling also revealed that, while the proton transfer event would be strongly discouraged in the gas phase, it occurs in the solid state due to the increase in charge state of the molecular ions and their arrangement inside the lattice. The color change is attributed to a narrowing of the squaric acid to bipyridine charge-transfer energy gap. Finally, evidence for the possible existence of two further phases at high pressure is also presented
0002-7863
3884-3893
Martins, David M.S.
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Middlemiss, Derek S.
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Pulham, Colin R.
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Wilson, Chick C.
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Weller, Mark T.
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Henry, Paul F.
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Shankland, Norman
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Marshall, William G.
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Ibberson, Richard M.
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Knight, Kevin
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Moggach, Stephen
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Brunelli, Michela
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Morison, Carole A.
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Martins, David M.S.
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Middlemiss, Derek S.
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Pulham, Colin R.
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Wilson, Chick C.
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Weller, Mark T.
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Henry, Paul F.
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Shankland, Norman
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Marshall, William G.
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Ibberson, Richard M.
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Knight, Kevin
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Moggach, Stephen
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Brunelli, Michela
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Morison, Carole A.
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Martins, David M.S., Middlemiss, Derek S., Pulham, Colin R., Wilson, Chick C., Weller, Mark T., Henry, Paul F., Shankland, Norman, Marshall, William G., Ibberson, Richard M., Knight, Kevin, Moggach, Stephen, Brunelli, Michela and Morison, Carole A. (2009) Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between quaric acid and 4,4?-bipyridine. Journal of the American Chemical Society, 131 (11), 3884-3893. (doi:10.1021/ja8082973).

Record type: Article

Abstract

We have applied a combination of spectroscopic and diffraction methods to study the adduct formed between squaric acid and bypridine, which has been postulated to exhibit proton transfer associated with a single-crystal to single-crystal phase transition at ca. 450 K. A combination of X-ray single-crystal and very-high flux powder neutron diffraction data confirmed that a proton does transfer from the acid to the base in the high-temperature form. Powder X-ray diffraction measurements demonstrated that the transition was reversible but that a significant kinetic energy barrier must be overcome to revert to the original structure. Computational modeling is consistent with these results. Modeling also revealed that, while the proton transfer event would be strongly discouraged in the gas phase, it occurs in the solid state due to the increase in charge state of the molecular ions and their arrangement inside the lattice. The color change is attributed to a narrowing of the squaric acid to bipyridine charge-transfer energy gap. Finally, evidence for the possible existence of two further phases at high pressure is also presented

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Published date: 2009

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Local EPrints ID: 158753
URI: http://eprints.soton.ac.uk/id/eprint/158753
ISSN: 0002-7863
PURE UUID: 50bbf4d0-acbc-476e-81f8-e0f1b8ebd458

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Date deposited: 23 Jun 2010 14:16
Last modified: 04 Nov 2019 21:03

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Contributors

Author: David M.S. Martins
Author: Derek S. Middlemiss
Author: Colin R. Pulham
Author: Chick C. Wilson
Author: Mark T. Weller
Author: Paul F. Henry
Author: Norman Shankland
Author: William G. Marshall
Author: Richard M. Ibberson
Author: Kevin Knight
Author: Stephen Moggach
Author: Michela Brunelli
Author: Carole A. Morison

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