X-ray photochemistry in iron complexes from Fe(0) to Fe(IV) - Can a bug become a feature?

Under intense soft X-ray irradiation, we have observed time-dependent changes in the soft X-ray spectra of virtually all the Fe coordination complexes that we have examined, indicating chemical transformation of the compound under study. Each compound, with oxidation states ranging from Fe(IV) to Fe(0), has been studied with either Fe L-edge spectroscopy or N K-edge spectroscopy. We find that very often a well-defined spectroscopic change occurs, at least initially, which is apparently capable of straightforward interpretation in terms of X-ray induced photoreduction, photooxidation or ligand photolysis. We briefly discuss the probable chemical nature of the changes and then estimate the rate of chemical change, thereby establishing the necessary radiation dose. We also demonstrate that the photochemistry not only depends on the Fe oxidation state but also the coordination chemistry of the complex. It seems that a proper understanding of such X-ray photochemical effects could well greatly assist the assignment of soft X-ray spectra of uncharacterized metal sites.