title: Electrochemical and Spectral Characterization of Iron Corroles in High and Low Oxidation States: First Structural Characterization of an Iron(IV) Tetrapyrrole pi Cation Radical.
abstract: The electrochemistry and spectroscopic properties of three iron corroles were examined in benzonitrile, dichloromethane, and pyridine containing 0.1 M tetra-n-butylammonium perchlorate or tetra-n-ethylammonium hexafluorophosphate as supporting electrolyte. The investigated compounds are represented as (OEC)Fe(IV)(C(6)H(5)), (OEC)Fe(IV)Cl, and (OEC)Fe(III)(py), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. Each iron(IV) corrole undergoes two one-electron reductions and two or three one-electron oxidations depending upon the solvent. Under the same solution conditions, the iron(III) corrole undergoes a single one-electron reduction and one or two one-electron oxidations. Each singly oxidized and singly reduced product was characterized by UV-vis and/or EPR spectroscopy. The data indicate a conversion of (OEC)Fe(IV)(C(6)H(5)) and (OEC)Fe(IV)Cl to their iron(III) forms upon a one-electron reduction and to iron(IV) corrole pi cation radicals upon a one-electron oxidation. The metal center in [(OEC)Fe(III)(C(6)H(5))](-) is low spin (S = (1)/(2)) as compared to electrogenerated [(OEC)Fe(III)Cl](-), which contains an intermediate-spin (S = (3)/(2)) iron(III). (OEC)Fe(III)(py) also contains an intermediate-spin-state iron(III) and, unlike previously characterized (OEC)Fe(III)(NO), is converted to an iron(IV) corrole upon oxidation rather than to an iron(III) pi cation radical. Singly oxidized [(OEC)Fe(IV)(C(6)H(5))](*)(+) is the first iron(IV) tetrapyrrole pi cation radical to be isolated and was structurally characterized as a perchlorate salt. It crystallizes in the triclinic space group P&onemacr; with a = 10.783(3) Å, b = 13.826(3) Å, c = 14.151(3) Å, alpha = 78.95(2) degrees, beta = 89.59(2) degrees, and gamma = 72.98(2) degrees at 293 K with Z = 2. Refinement of 8400 reflections and 670 parameters against F(o)(2) yields R1 = 0.0864 and wR2 = 0.2293. The complex contains a five-coordinated iron with average Fe-N bond lengths of 1.871(3) Å. The formulation of the electron distribution in this compound was confirmed by Mössbauer, X-ray crystallographic, and magnetic susceptibility data as well as by EPR spectroscopy, which gives evidence for strong antiferromagnetic coupling between the iron(IV) center and the singly oxidized corrole macrocycle.
authors.affiliation: Department of Chemistry, University of Houston, Houston, Texas 77204-5641, Institut für Organische Chemie, Universität zu Köln, Greinstrasse 4, D-50939 Köln, Germany, and Département de Chimie, URA CNRS 405, Université Louis Pasteur, 67000 Strasbourg, France.
authors.forename: Eric Van
authors.initials: EV
authors.lastname: Caemelbecke
authors.forename: Stefan
authors.initials: S
authors.lastname: Will
authors.forename: Marie
authors.initials: M
authors.lastname: Autret
authors.forename: Victor A.
authors.initials: VA
authors.lastname: Adamian
authors.forename: Johann
authors.initials: J
authors.lastname: Lex
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Gisselbrecht
authors.forename: Maurice
authors.initials: M
authors.lastname: Gross
authors.forename: Emanuel
authors.initials: E
authors.lastname: Vogel
authors.forename: Karl M.
authors.initials: KM
authors.lastname: Kadish