The evolution of hydrogen atom parameters under changing external conditions by time-of-flight single crystal neutron diffraction

Abstract

Recent studies performed by our group, of hydrogen atom behaviour in hydrogen bonds as a function of external variable, are reviewed. The changes observed, often manifest in the form of proton disorder or apparent migration, open up the intriguing possibility of being able to alter the behaviour of hydrogen bonds. This work has only been made possible by developments in data collection methods that allow evolving molecular structures to be studied at unprecedented numbers of temperatures and pressures by neutron single crystal diffraction. It is shown that even more insight is possible by complementing such studies with imaging of hydrogen bonds using X-ray methods, together with using computational studies to try to shed additional light on the underlying potentials.

Keywords:

• Hydrogen atom parameters
• Hydrogen bonds
• Structural evolution
• Proton transfer and disorder
• Neutron single crystal diffraction
• Computational chemistry

Acknowledgements

The author would like to thank the many collaborators with whom he has worked, and in many cases is still working, on many of the systems discussed here. These include Nick Blagden, Richard Cooper, Philip Camp, Alastair Florence, Chris Frampton, Matthias Gutmann, Tony Horsewill, Judith Howard, Mark Johnson, Cara Nygren, Andres Goeta, Harriott Nowell, David Keen, Irene Majerz, Carole Morrison, Andy Parkin, Colin Pulham, Colin Seaton, Kenneth Shankland, Norman Shankland, Thomas Steiner and John Turner. Members of the Wilson research group who have contributed to the work presented here and related topics include Martin Adam, Suzanne Harte, Derek Middlemiss, Marc Schmidtmann and Lynne Thomas. Victoria Nield is thanked for her encouragement and constructive criticism in preparing this article, and the author has benefited from discussions with Hans-Beat Bürgi, Jack Dunitz, John Helliwell, Garry McIntyre and Paul Raithby. Parts of this work were funded under EPSRC grants GR/L71902, GR/M41773, GR/R04690 and GR/T21615. Additional funding from CCLRC and the University of Glasgow is acknowledged. Beamtime and technical support at ISIS have been invaluable in allowing much of this work to be carried out.