title: HFEPR and Computational Studies on the Electronic Structure of a High-Spin Oxidoiron(IV) Complex in Solution.
abstract: Nonheme iron enzymes perform diverse and important functions in biochemistry. The active form of these enzymes comprises the ferryl, oxidoiron(IV), [FeO](2+) unit. In enzymes, this unit is in the high-spin, quintet, S = 2, ground state, while many synthetic model compounds exist in the spin triplet, S = 1, ground state. Recently, however, Que and co-workers reported an oxidoiron(IV) complex with a quintet ground state, [FeO(TMG3tren)](OTf)2, where TMG3tren = 1,1,1-tris{2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl}amine and OTf = CF3SO3(-). The trigonal geometry imposed by this ligand, as opposed to the tetragonal geometry of earlier model complexes, favors the high-spin ground state. Although [FeO(TMG3tren)](2+) has been earlier probed by magnetic circular dichroism (MCD) and Mössbauer spectroscopies, the technique of high-frequency and -field electron paramagnetic resonance (HFEPR) is superior for describing the electronic structure of the iron(IV) center because of its ability to establish directly the spin-Hamiltonian parameters of high-spin metal centers with high precision. Herein we describe HFEPR studies on [FeO(TMG3tren)](OTf)2 generated in situ and confirm the S = 2 ground state with the following parameters: D = +4.940(5) cm(-1), E = 0.000(5), B4(0) = -14(1) × 10(-4) cm(-1), g⊥ = 2.006(2), and g∥ = 2.03(2). Extraction of a fourth-order spin-Hamiltonian parameter is unusual for HFEPR and impossible by other techniques. These experimental results are combined with state-of-the-art computational studies along with previous structural and spectroscopic results to provide a complete picture of the electronic structure of this biomimetic complex. Specifically, the calculations reproduce well the spin-Hamiltonian parameters of the complex, provide a satisfying geometrical picture of the S = 2 oxidoiron(IV) moiety, and demonstrate that the TMG3tren is an "innocent" ligand.
authors.affiliation: Institute of Physical Chemistry and Chemical Physics, Faculty of Chemical and Food Technology, Slovak University of Technology , Radlinského 9, SK-81237 Bratislava, Slovakia.
authors.forename: Lukas
authors.initials: L
authors.lastname: Bucinsky
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Rohde
authors.affiliation: Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota , Minneapolis, Minnesota 55455, United States.
authors.forename: Lawrence
authors.initials: L
authors.lastname: Que
authors.affiliation: National High Magnetic Field Laboratory, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: Andrew
authors.initials: A
authors.lastname: Ozarowski
authors.affiliation: National High Magnetic Field Laboratory, Florida State University , Tallahassee, Florida 32310, United States.
authors.forename: J
authors.initials: J
authors.lastname: Krzystek
authors.affiliation: Institute of Physical Chemistry and Chemical Physics, Faculty of Chemical and Food Technology, Slovak University of Technology , Radlinského 9, SK-81237 Bratislava, Slovakia.
authors.forename: Martin
authors.initials: M
authors.lastname: Breza
authors.affiliation: Department of Biological, Chemical and Physical Sciences, Roosevelt University , Chicago, Illinois 60605, United States.
authors.forename: Joshua
authors.initials: J
authors.lastname: Telser
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D058085:Iron Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D011789:Quantum Theory; D012996:Solutions
chemical_list: D058085:Iron Compounds; D012996:Solutions