Probing Physical Oxidation State by Resonant X-ray Emission Spectroscopy: Applications to Iron Model Complexes and Nitrogenase

The ability of resonant X-ray emission spectroscopy (XES) to recover physical oxidation state information, which may often be ambiguous in conventional X-ray spectroscopy, is demonstrated. By combining K beta XES with resonant excitation in the XAS pre-edge region, resonant K beta XES (or 1s3p RXES) data are obtained, which probe the 3d(n+1) final-state configuration. Comparison of the non-resonant and resonant XES for a series of high-spin ferrous and ferric complexes shows that oxidation state assignments that were previously unclear are now easily made. The present study spans iron tetrachlorides, iron sulfur clusters, and the MoFe protein of nitrogenase. While 1s3p RXES studies have previously been reported, to our knowledge, 1s3p RXES has not been previously utilized to resolve questions of metal valency in highly covalent systems. As such, the approach presented herein provides chemists with means to more rigorously and quantitatively address challenging electronic-structure questions.

Automated summary

Resonant X-ray emission spectroscopy (XES) is demonstrated to be able to recover physical oxidation state information in highly covalent systems, providing a straightforward way to resolve previously ambiguous oxidation state assignments. This approach offers chemists a more rigorous and quantitative method to address challenging electronic-structure questions.