Applied X-ray spectroscopy

X-ray induced changes in small molecular crystals

Our most recent work, led by Nathalie Fernando, focuses on a subject matter typically considered a nuisance to many experimentalists who use X-rays. That is, the X-ray induced changes to the sample being probed. X-rays feature in many characterisation techniques today but are often (incorrectly!) regarded as non-destructive. In recent years, these unwanted X-ray-matter effects have been worsened by X-ray sources, both lab and synchrotron based, with ever increasing brightness. These X-ray induced phenomena have been widely studied in macromolecular crystallography, but unfortunately, the same cannot be said for small molecular crystals.

Recently published in the Journal of Physical Chemistry A, (available also as a preprint on ChemRxiV) our paper is the culmination of a huge collaborative effort comprising of crystallographers, spectroscopists, and theorists.

Here, we explore the effects of X-ray irradiation on two industrially important catalysts [Ir(COD)Cl]2 and [Rh(COD)Cl]2, using synchrotron-based X-ray diffraction and laboratory-based X-ray photoelectron spectroscopy. Both single crystal and powder X-ray diffraction were used to obtain a detailed understanding of the changes in structure and atomic positions upon irradiation. This was only possible through the close collaboration with an amazing team of crystallographers, including Dr Andrew Cairns (Imperial College London), Dr Claire Murray (Diamond Light Source), and Dr Amber Thompson (University of Oxford). Crystallography and spectroscopy, with density functional theory calculations, led by Dr. Laura Ratcliff (Imperial College London) and with the support of Nayera Ahmed, an MSci student in the group, provide insights into the structural, chemical, and electronic changes taking place within the samples upon X-ray irradiation. Crucially, these changes are studied with respect to X-ray dose, using the RADDOSE-3D software, with the support of Dr. Joshua Dickerson and Prof. Elspeth Garman at the University of Oxford. 

This work presents an important first step towards understanding the changes in small molecular systems due to X-ray irradiation, and we hope that the combination of techniques outlined, will form the basis of many future systematic X-ray damage studies on a wide range of important small molecular materials.

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