Synchrotron X-ray Diffraction Studies of Proton Transfer in Hydrogen Bonded Molecular Complexes

Abstract

The technique of single crystal synchrotron X-ray diffraction is applied in the study of solid state proton transfer processes in hydrogen bonded molecular complexes. Proton transfer processes are of interest where they are responsible for a number of physical and chemical properties within solid state functional materials; their study gives insight into the occurrence of such properties and where they may be targeted and tuned in future materials. The synchrotron X-ray diffraction technique has been trialled with respect to the potential it offers for high throughput capability for studying proton transfer processes as a function of an external stimulus or across a number of molecular systems. Chapter 1 contains a review of the literature of the hydrogen bond, including its role in crystal engineering and proton transfer effects. In Chapter 2, the theory behind the analytical techniques used in the study of hydrogen bonded molecular complexes, in which crystallographic methods are fundamental, are described. In Chapter 3 the research project aims and objectives are presented; these objectives are targeted at the use of single crystal synchrotron X-ray diffraction in the study and rationalisation of solid state proton transfer processes. In Chapter 4, the experimental methods implemented in this research project to achieve these research goals are reported. Chapter 5 is the first of the result chapters and applies the synchrotron single crystal X-ray diffraction technique in the study of variable temperature proton disorder in centrosymmetric hydrogen bonded carboxylic acid dimers. Chapter 6 focuses on the design of proton transfer systems implementing a number of crystal engineering strategies in the design of short strong hydrogen bonds (SSHBs) for potential proton migration studies. Chapter 7 applies a combination of diffraction methods (synchrotron and laboratory X-ray diffraction) and refinement strategies in the study of temperature dependent proton migration across SSHBs, allowing the potential of these methods in the study of proton migration to be assessed. Chapter 8 is the final application of the synchrotron technique in studies of proton transfer behaviour investigating static proton transfer behaviour in molecular complexes of the proton sponge 1,8-bis(dimethylamino)naphthalene with organic acids. The urea-acid inclusion materials presented in Chapter 9 additionally allow the investigation of the hydrogen bond as a crystal engineering tool in the design of hydrogen bonded solvent-inclusion networks.In the last chapter, Chapter 10, conclusions from the findings in Chapters 5 to 9 are pulled together and patterns explored. Drawing on these overall findings, some suggestions for future work are also made.

Date of Award	4 Nov 2016
Original language	English
Awarding Institution	University of Bath
Sponsors	Diamond Light Source Ltd
Supervisor	Chick Wilson (Supervisor), Paul Raithby (Supervisor) & Harriott Nowell (Supervisor)