Insights into the Structure of Reaction Intermediates Through Coupled X-ray Absorption/UV-Vis Spectroscopy

In this work, we propose a method for the structural characterization of chemical reaction intermediates. It allows one to analyze time-resolved coupled energy dispersive X-ray absorption spectroscopy (EDXAS) and UV-Vis reaction data through a matricial approach. Concentration profiles for the reaction key species are derived from the UV-Vis data and are used as mathematical constraints to extract their associated X-ray absorption near edge structure (XANES) spectra. The obtained XANES spectra are then quantitatively characterized by full multiple scattering (MS) calculations. We demonstrate the capabilities of this approach by applying it over a series of coupled EDXAS/UV-Vis spectra acquired in the reaction between \(\mathrm{Fe}^{II}\)(tris(2-pyridylmethyl)amine) (\([\mathrm{Fe}^{II}(\mathrm{TPA})(\mathrm{CH}_3\mathrm{CN})_2]^{2+}\)) and \(\mathrm{H}_2\mathrm{O}_2\). As a result, structural information for the elusive reaction key intermediate \([\mathrm{Fe}^{III}\)(TPA)(OOH)(X)]\(^{2+}\) is derived and it is suggested that \(\mathrm{X}=\mathrm{CH}_3\mathrm{CN}\) in opposition to \(\mathrm{X}=\mathrm{H}_2\mathrm{O}\).