A signal through the noise: accurate determination of hydrogen atom positions in crystal structures and optimisation of Laue neutron diffraction methods

In this thesis, Laue neutron diffraction methods are applied to determine the positions of hydrogen atoms in crystal structures accurately and with confidence, as well as informing the optimisation and development of these methods. This has allowed a variety of chemically and crystallographically interesting studies to be performed, specifically: Determining the novel geometry around transition-metal hydride centers, where the signal due to the hydrides can be more confidently distinguished than in an X-ray diffraction experiment; using Laue neutron derived difference Fourier maps to demonstrate that proton disorder can be mistakenly assigned in X-ray derived crystallographic models; performing variable temperature Laue neutron diffraction to identify proton migratory behaviour across short-strong hydrogen bonds; reassigning the space group of a previously reported cobalt(III) coordination complex, in which the lack of inversion symmetry becomes apparent upon accurate determination of the hydrogen atom positions; using Laue neutron diffraction data to more confidently classify systems as co-crystals or salts. Following this, the optimisation and development of the Laue neutron diffraction methods used is described. This focuses on: Recommendations for the efficient collection of Laue neutron data, in order to optimise the data set completeness and awarded beam-time; strategic considerations for how to best answer the scientific question(s) at hand in a Laue neutron experiment, whilst planning against future contingencies; improving methods for crystal packing and shipping, particularly for air and moisture sensitive materials; discussing issues arising from ice forming on the crystal during a Laue neutron diffraction experiment, and methods for minimising this problem; more effectively modelling disorder using ring shapes, in the crystallographic refinement package CRYSTALS; providing rationale for Laue neutron specific checkCIF comments. Alongside the aforementioned research projects, the relevant history and theory contextualising the crystallographic methods used is presented.