title: The coordination chemistry of FeCl3 and FeCl2 to bis[2-(2,3-dihydroxyphenyl)-6-pyridylmethyl](2-pyridylmethyl)amine: access to a diiron(III) compound with an unusual pentagonal-bipyramidal/square-pyramidal environment.
abstract: Coordination of FeCl3 to the title ligand yields a mononuclear iron(III) complex 1, which was characterized by spectroscopic techniques and X-ray diffraction. The ligand is (kappa3-N) tridentate and the metal, which lies in a pseudo-octahedral environment, is bound to a phenolate group from the catechol substituent. The dichloroiron(II) complex 2 was easily obtained by metalation of the ligand with FeCl2 and characterized by various spectroscopic techniques. In their cyclic voltammograms both 1 and 2 display the same reversible FeII/FeIII wave at E1/2=10 mV (vs. SCE). Reduction of compound 1 with Zn/Hg yields 2', which displays identical properties to 2. Taken together, these findings indicate that in spite of the different oxidation state of the metal in 2, no major geometrical/structural change is observed at the metal center with respect to 1. The reaction of 2 with dioxygen in the absence of organic substrates proceeds extremely rapidly and yields compound 3, which is a diiron(III) derivative whose X-ray crystal structure is also reported. The possibility of a radical-based mechanism is discussed. Compound 3 displays an unusual geometry: one iron(III) center is seven-coordinate, whereas the other lies in a square-pyramidal environment. The two iron atoms are bridged by the catecholato substituents. To the best of our knowledge, 3 is the first example of a seven-coordinate iron(III) derivative with tris(2-pyridylmethyl)amine ligands.
authors.affiliation: Laboratoire de Chimie Biomimetique des Metaux de Transition, Institut de Chimie, UMR CNRS no. 7177-LC3, Université Louis Pasteur, Institut Le Bel, 4 rue Blaise Pascal, 67070 Strasbourg cedex, France.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Machkour
authors.forename: Nasser K
authors.initials: NK
authors.lastname: Thallaj
authors.forename: Laila
authors.initials: L
authors.lastname: Benhamou
authors.forename: Mohammed
authors.initials: M
authors.lastname: Lachkar
authors.forename: Dominique
authors.initials: D
authors.lastname: Mandon
mesh_terms: D002712:Chlorides; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D008024:Ligands; D008628:Mercury / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry
chemical_list: D002712:Chlorides; D005290:Ferric Compounds; D005296:Ferrous Compounds; D008024:Ligands; D011725:Pyridines; C431843:tris(2-pyridylmethyl)amine; D008628:Mercury; D015032:Zinc; C029451:ferrous chloride; C024555:ferric chloride