Investigating discontinuous X-ray irradiation as a damage mitigation strategy for [M(COD)Cl]₂ catalysts

With the advent of ever more intense and focused X-ray sources, including in laboratories, at synchrotrons, and at X-ray free electron lasers, radiation-induced sample change and damage are becoming increasingly challenging. Therefore, the exploration of possible mitigation strategies is crucial to continue to allow the collection of robust and repeatable data. One mitigation approach is the introduction of short, X-ray-free "dark" periods. However, it is unclear whether this strategy minimises damage or, in actuality, promotes it through a phenomenon called "dark progression", <i>i.e.</i> the increase or progression of radiation damage that occurs after the X-ray beam is turned off. This work discusses the influence of introducing dark periods and their duration on the radiation-induced changes in two model small-molecule catalysts, [Ir(COD)Cl]₂ and [Rh(COD)Cl]₂, exposed to X-ray radiation in synchrotron powder diffraction (PXRD) and laboratory photoelectron spectroscopy (XPS) experiments. This provides, for the first time, insights into how damage progresses under varying radiation regimes and allows the distinction between the processes that affect the unit cell itself, the individual molecular units, and the respective atomic chemical environments. Furthermore, it provides the basis for informed decision-making in the design of future experiments where the need to minimise radiation-induced damage is crucial.