Oxygen bridged binuclear complexes

Mononuclear hydroxocomplexes have been identified in studies on Fe(edta) and Fe(nta), but dimerization to (edta)FeOFe(edta) - is well established (53), and further oxygen-bridged binuclear complexes of Fe(III) have been characterized (54). Polynuclear hydroxocomplexes Fe (OH)2 7m (55) formed in chloride media at 1.8 < pH <2.3 do not react with TMPyP within one week, nor do mononuclear complexes of Fe(III) containing CHsCOi, N3, C20, (H3L =... 

The key issue for RR spectroscopists dealing with non-haem iron proteins is to determine the geometry of the oxygen-bridged binuclear complexes as well as to identify the nature of the ligands. In these studies, the RR spectra of i 0-labelled samples significantly supports the interpretation. 

Figure 9 A few schematic examples of mononuclear Fe(II) -porphyrin derivatives used to prevent the irreversible oxidation to oxygen-bridged binuclear Fe(III) derivatives. (a) Picket-fence complexes (b) strapped complexes (c) capped complexes (d) picnic-basket complexes (e) pocket complexes...

Some preparations of iron exchanged into zeolite H-MFI by vapor-phase FeCL are known to be active and selective catalysts for the reduction of NO, with hydrocarbons or ammonia in the presence of excess oxygen and water vapor (45,46). The active centers in Fe/MFI are assumed to be binuclear, oxygen-bridged iron complexes, as follows from H2-TPR, CO-TPR, and ESR data (45,47) and EXAFS and XANES results (48,49). These complexes are structurally similar to the binuclear iron centers in methane monooxygenase enzymes that are employed by methanotrophic bacteria in utilization of methane as their primary energy source (50). It is believed that molecular oxygen reacts with these centers to form peroxide as the initial step in this chemistry (50). 

Binuclear, oxygen-bridged Fe111 complexes have been actively studied in recent years.23 Two types, dihydroxo- and monooxo-bridged ones have been recognized. The former are represented by [Fe(H20)4OH]2, mentioned above and by [Fe(pic)2OH]2 [pic is the anion (25-E-II)]. Neither has been definitively... 

These conclusions are supported by another ESR study (Jd) made on some oxygenated cobaltoximes(II), which showed that the dioxygen species finally formed is best characterized as a peroxo-bridged complex these being reversibly formed binuclear complexes. 

A similar type of oxygen complex has been observed during the oxidation of [Con(CN) s]-3 but it was not possible to show that this species was formed in the initial reaction step since with this system, as with the cobaloxime(II) system, the 1 1 adduct apparently reacts very rapidly with another molecule of pentacyanocobaltate(II) to form a diamagnetic binuclear complex with a bridging peroxide ligand 116). It appears that in the Bi2-system the bulk of the corrin ring does not allow formation of the diamagnetic binuclear complex. 

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