Showing papers by "Jean-Jacques Girerd published in 2000"

Characterization and Properties of Non-Heme Iron Peroxo Complexes

Abstract: Iron-peroxo Fe(III)O2 and hydroperoxo Fe(III)OOH systems are important intermediates between the initial Fe(II)-dioxygen adduct and the “activated” form of the catalytic site in many mono-iron biomolecules. To the same peroxidic level correspond, in diiron enzymes, bridged peroxo Fe(III)-O-O-Fe(III) intermediates. This review is concerned with the preparation and spectroscopic characterization of such intermediates in non-heme chemical systems, the properties of the natural systems being quoted as references. Although none have been crystallized, it seems very likely that Fe(III)OOH systems present a η 1 - coordination mode for the hydroperoxo group. These Fe(III)OOH units have given clear signatures in UV-vis, resonance Raman and mass spectrometry. By EPR it was found that in Fe(III)OOH, the Fe(III) is low-spin (S = 1/2) and we propose here a simple rationalization of the characteristics of the EPR g-tensor. The electronic properties of the Fe(III)(η1-OOH) known so far, point toward a strong Fe-O bond and a weak O-O bond, in total agreement with the reactivity scheme implying a cleavage of the O-O bond to lead formally to a Fe(V)O unit. Alkylperoxo systems are also included in this review. Fe(III)-peroxo systems Fe(III)O2 have been prepared and described. They contain high-spin Fe(III) and those identified seem to be of the η 2 type. The Fe-O bond is weaker and the O-O one is stronger than in the Fe(III)OOH systems. The implication of these Fe(III)O2 units in catalysis is unclear. “Complementary” systems, such as Fe(III)(η 1-OO) or Fe(III)(η 2-OOH) have been evoked in publications but not identified spectroscopically. These systems certainly deserve to be actively looked for.

FeIII‐Hydroperoxo and Peroxo Complexes with Aminopyridyl Ligands and the Resonance Raman Spectroscopic Identification of the Fe−O and O−O Stretching Modes

Abstract: Nonheme Fe(III)-hydroperoxo and Fe(III)-peroxo complexes with aminopyridyl-type ligands have been prepared and characterized by UV/Vis, EPR, mass and Resonance Raman (RR) spectroscopy. The Fe(III)(OOH) species are low-spin and exhibit a deep purple color due to the ligand-to-metal charge transfer (LMCT) hand centered at ca. 550 nm. The RR spectra of the Fe(III)(OOH) complexes display two bands at ca. 620 and 800 cm-1 that are assigned to the respective Fe-O and O-O stretching modes on the basis of the characteristic H/D and 16O/18O frequency shifts. Upon deprotonation, Fe(III)(O2) species are obtained which possess a high-spin configuration of nearly axial symmetry and a LMCT transition in the near infrared (ca. 750 nm). The frequencies of the Fe-O and O-O stretching modes at ca. 465 and 820 cm-1, as well as their respective 16O/18O shifts of -16 and -45 cm-1, indicate an ?2 coordination geometry for the Fe(III)(O2) complex.

A Two-Step Spin Crossover in

Abstract: Measurement of magnetic susceptibility with temperature of a powdered iron(III) catecholate complex clearly indicated a two-step spin-crossover process S=(1/2) S=5/2. The picture shows the plot of chi(M)T against temperature.