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Title: L-Edge X-ray Absorption Spectroscopic Investigation of {FeNO} 6: Delocalization vs Antiferromagnetic Coupling

NO is a classic non-innocent ligand, and iron nitrosyls can have different electronic structure descriptions depending on their spin state and coordination environment. These highly covalent ligands are found in metalloproteins and are also used as models for Fe–O 2 systems. Here, this study utilizes iron L-edge X-ray absorption spectroscopy (XAS), interpreted using a valence bond configuration interaction multiplet model, to directly experimentally probe the electronic structure of the S = 0 {FeNO} 6 compound [Fe(PaPy 3)NO] 2+ (PaPy 3 = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) and the S = 0 [Fe(PaPy 3)CO] + reference compound. This method allows separation of the σ-donation and π-acceptor interactions of the ligand through ligand-to-metal and metal-to-ligand charge-transfer mixing pathways. The analysis shows that the {FeNO} 6 electronic structure is best described as Fe III–NO(neutral), with no localized electron in an NO π* orbital or electron hole in an Fe dπ orbital. This delocalization comes from the large energy gap between the Fe–NO π-bonding and antibonding molecular orbitals relative to the exchange interactions between electrons in these orbitals. This study demonstrates the utility of L-edge XAS in experimentally defining highly delocalized electronic structures.
ORCiD logo [1] ;  [2] ; ORCiD logo [3] ;  [4] ;  [5] ;  [5]
  1. Stanford Univ., CA (United States). Dept. of Chemistry
  2. Foothill College, Los Altos Hills, CA (United States). Dept. of Chemistry
  3. Univ. of California, Santa Cruz, CA (United States). Dept. of Chemistry and Biochemistry
  4. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  5. Stanford Univ., CA (United States). Dept. of Chemistry; SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; CHE-0957251; CHE-1360046; P41GM103393; R01GM040392
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 3; Journal ID: ISSN 0002-7863
American Chemical Society (ACS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Institutes of Health (NIH); National Science Foundation (NSF); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
OSTI Identifier: