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

Chemistry. 2006 Aug 25;12(25):6660-8. doi: 10.1002/chem.200600276.

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.

MeSH terms

  • Chlorides
  • Crystallography, X-Ray
  • Ferric Compounds / chemistry*
  • Ferrous Compounds / chemistry*
  • Ligands
  • Mercury / chemistry
  • Molecular Structure
  • Oxidation-Reduction
  • Pyridines / chemistry*
  • Spectrophotometry, Ultraviolet
  • Zinc / chemistry

Substances

  • Chlorides
  • Ferric Compounds
  • Ferrous Compounds
  • Ligands
  • Pyridines
  • tris(2-pyridylmethyl)amine
  • Mercury
  • Zinc
  • ferrous chloride
  • ferric chloride