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Abstract Understanding the electronic structures of high‐valent metal complexes aids the advancement of metal‐catalyzed cross coupling methodologies. A prototypical complex with formally high valency is [Cu(CF3)4]−(1), which has a formal Cu(III) oxidation state but whose physical analysis has led some to a Cu(I) assignment in an inverted ligand field model. Recent examinations of1by X‐ray spectroscopies have led previous authors to contradictory conclusions, motivating the re‐examination of its X‐ray absorption profile here by a complementary method, resonant diffraction anomalous fine structure (DAFS). From analysis of DAFS measurements for a series of seven mononuclear Cu complexes including1, here it is shown that there is a systematic trifluoromethyl effect on X‐ray absorption that blue shifts the resonant Cu K‐edge energy by 2–3 eV per CF3, completely accounting for observed changes in DAFS profiles between formally Cu(III) complexes like1and formally Cu(I) complexes like (Ph3P)3CuCF3(3). Thus, in agreement with the inverted ligand field model, the data presented herein imply that1is best described as containing a Cu(I) ion with dncount approaching 10.
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Ultrafast Light‐Driven Electronic and Structural Changes in LaFeO 3 Perovskites Probed by Femtosecond X‐Ray Absorption Spectroscopy
Abstract Conducting real‐time, element‐specific studies of photo‐excited systems is a long‐standing challenge. The development of X‐ray free‐electron lasers (XFELs) has paved the way for the emergence of a promising technique: femtosecond X‐ray absorption spectroscopy (fs‐XAS). This powerful technique reveals electronic and geometric characteristics, providing unprecedented insight into their dynamic interactions under nonequilibrium conditions. Herein, the fs‐XAS technique is employed at PAL‐XFEL to unravel light‐driven ultrafast electronic and structural changes in epitaxial lanthanum iron oxide (LaFeO3) thin films. Density functional theory (DFT) and multiplet calculations are utilized to expound on the experimental results. The analyses reveal that photoexcitation initially induces high‐ and intermediate‐spin Fe2+states through ligand‐to‐metal charge transfer (LMCT), followed by polaron formation. It is demonstrated that the reduced overlap between the oxygen 2pand iron 3dorbitals accounts for all experimental observations, including 1) the XAS shifts to lower energies, 2) the decrease in the crystal field splitting, and 3) the relatively larger shifts observed in the oxygen 1sXAS.
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- Award ID(s):
- 2309000
- PAR ID:
- 10651264
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 37
- Issue:
- 29
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/adma.202502932
