Fernando, Nathalie Kanchena; (2023) Structural & Electronic Effects of X-ray Radiation on Small Molecule Crystals. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

X-rays are indispensable to many advanced characterisation techniques for probing properties of matter. Although often regarded as non-destructive, interactions of X-rays with crystalline matter are widely known to induce sample changes. Despite the undesirable consequences of radiation being well documented in macromolecular crystallography since the 1960s, knowledge of its influence on small molecule crystals, which are integral to many modern applications for instance, catalysis, remains incredibly limited. In recent years, the shift towards microfocused laboratory sources and higher brilliance synchrotrons has exacerbated the problem of unwanted radiation effects, increasing the necessity for a better understanding of its influence on matter and characterisation results. This body of work provides a comprehensive analysis of the impact of X-rays on a family of industrially important transition metal complexes with the formula [M(COD)Cl]₂ where M= group 8-11 transition metals and COD= cyclooctadiene. A combined experimental and computational approach of synchrotron powder X-ray diffraction, laboratory-based X-ray photoelectron spectroscopy and density functional theory, is implemented to infer radiation-induced changes to the structure, local chemical environments, and electronic structure of these systems. The progression of damage is monitored over considerable timescales and discussed within the context of radiation dose, a relatively new concept in small molecule crystallography. The contribution of various experimental conditions to radiation-induced sample change, such as X-ray energy, temperature, and measurement environment, is also investigated. Employing a combined approach of XRD, XPS and DFT has allowed for a compelling, multi-modal way to probe effects of X-ray irradiation, by way of a direct correlation of structural changes with changes of the electronic structure and chemical state of the metal. There is enormous potential to extend the application of these three advanced techniques beyond this family of organometallic catalysts, to follow X-ray-induced effects and apply findings, to other small molecule systems of scientific or industrial relevance.

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