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 Kβ XES with resonant excitation in the XAS pre‐edge region, resonant Kβ XES (or 1s3p RXES) data ar...

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Bibliographic Details
Published in:Angewandte Chemie 2021-04, Vol.133 (18), p.10200-10209
Main Authors: Castillo, Rebeca G., Hahn, Anselm W., Van Kuiken, Benjamin E., Henthorn, Justin T., McGale, Jeremy, DeBeer, Serena
Format: Article
Language:English
Subjects:
Chemistry
Chemists
Coordination compounds
Emission spectroscopy
Iron
iron complexes
MoFe protein
molybdenum
Nitrogenase
Oxidation
oxidation states
Questions
Spectroscopy
Spectrum analysis
Sulfur
Tetrachlorides
Valence
valence-to-core X-ray emission spectroscopy
Valency
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Summary: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 Kβ XES with resonant excitation in the XAS pre‐edge region, resonant Kβ XES (or 1s3p RXES) data are obtained, which probe the 3dn+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. Assigning transition‐metal physical oxidation states is a major goal of X‐ray spectroscopy. However, competing influences of covalency and d‐count on Kβ XES spectra often make assignments ambiguous. It is now shown that resonant Kβ X‐ray emission spectroscopy (RXES) yields unambiguous oxidation‐state determinations for iron monomers, dimers, cubanes, and metalloenzymes.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.202015669