Picture of wind turbine against blue sky

Open Access research with a real impact...

The Strathprints institutional repository is a digital archive of University of Strathclyde research outputs.

The Energy Systems Research Unit (ESRU) within Strathclyde's Department of Mechanical and Aerospace Engineering is producing Open Access research that can help society deploy and optimise renewable energy systems, such as wind turbine technology.

Explore wind turbine research in Strathprints

Explore all of Strathclyde's Open Access research content

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

Martins, D.M.S. and Middlemiss, D.S. and Pulham, C.R. and Wilson, C.C. and Weller, M.T. and Henry, P.F. and Shankland, N. and Shankland, K. (2009) Temperature- and pressure-induced proton transfer in the 1:1 adduct formed between squaric acid and 4,4'-bipyridine. Journal of the American Chemical Society, 131 (11). pp. 3884-3893. ISSN 0002-7863

Full text not available in this repository. (Request a copy from the Strathclyde author)

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.