title: L-Edge X-ray Absorption Spectroscopic Investigation of {FeNO}6: Delocalization vs Antiferromagnetic Coupling.
abstract: 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-O2systems. 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}6compound [Fe(PaPy3)NO]2+(PaPy3= N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) and the S = 0 [Fe(PaPy3)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}6electronic structure is best described as FeIII-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.
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.
authors.forename: James J
authors.identifier: 0000-0001-5516-3446
authors.initials: JJ
authors.lastname: Yan
authors.affiliation: Department of Chemistry, Foothill College , Los Altos Hills, California 94022, United States.
authors.forename: Margarita A
authors.initials: MA
authors.lastname: Gonzales
authors.affiliation: Department of Chemistry and Biochemistry, University of California , Santa Cruz, California 95064, United States.
authors.forename: Pradip K
authors.identifier: 0000-0002-7044-944X
authors.initials: PK
authors.lastname: Mascharak
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University , Menlo Park, California 94025, United States.
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.|Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University , Menlo Park, California 94025, United States.
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
authors.affiliation: Department of Chemistry, Stanford University , Stanford, California 94305, United States.|Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University , Menlo Park, California 94025, United States.
authors.forename: Edward I
authors.initials: EI
authors.lastname: Solomon
mesh_terms: D000577:Amides / Q000737:chemistry*; D004583:Electrons; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D056928:X-Ray Absorption Spectroscopy
chemical_list: D000577:Amides; C431605:N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide; D011725:Pyridines