NO Disproportionation Reactivity of Fe Tropocoronand Complexes

Abstract

The synthesis and characterization of divalent 5)] (1) and trivalent [Fe(OTf)(TC-5,5)] (2) tropocoronand complexes are described. Compound 1 reacts with 1 equiv of NO to form the {FeNO} 7 complex 3. A single-crystal X-ray structure determination of 3 reveals a trigonal bipyramidal geometry with a linearly coordinated nitrosyl (Fe-N-O ) 174.3(4)°) having a short Fe-N distance of 1.670(4) Å. EPR and Mo ¨ssbauer spectroscopy, SQUID susceptometry, and normal coordinate analysis indicate 3 to be a low-spin {Fe III (NO -)} 2+ species. In the presence of excess NO, 3 converts to a metastable nitrosyl-nitrito complex that decomposes by losing NO 2 , which subsequently nitrates the aromatic tropolone rings of the ligand. The final products of the NO disproportionation reaction are N 2 O and [Fe(NO)(TC-5,5-NO 2 )] (4). The ν NO stretching band of 4 is increased to 1716 cm -1 from its value of 1692 cm -1 in 3, owing to the electron-withdrawing nitro groups on the ligand, and the compound no longer promotes the disproportionation of NO. Mechanistic aspects of the reaction are discussed.

Cobalt(II) Complexes with Nitrogen Donors and Their Dioxygen Affinity in Dimethyl Sulfoxide

“…The OϪSϪC angles [104.08 (20)°] are also average for corresponding angles found in the literature for 400 related metalϪsulfoxide complexes and less than that in free dmso [105.7(2)°], whereas the CϪSϪC bond angles (Table 3) are almost similar to the corresponding values in free dmso (98.6°). [25] The perchlorate anions are not coordinated to the central Co II ion and therefore they are not reported in Figure 4.…”

Direct inhibition by nitric oxide of the transcriptional ferric uptake regulation protein via nitrosylation of the iron

“…However, the first, direct structural insight concerning the g ϭ 2.03 family has been obtained with a bis-imidazole-coordinated complex mimicking histidine residues (34). In addition, some mononitrosyl-iron complexes containing nitrogen donor ligands also exhibit these types of EPR features (35,36). Recent data concerning the nature of the ligands coordinated to iron in FeFur are much more in agreement with the environments in these compounds.…”

“…UV-visible spectra (not shown) revealed three bands at 310, 365, and 400 nm, characteristic of charge-transfer bands observed with small NO-iron complexes (35)(36)(37)(38). The appearance of these bands grew in parallel with the increase of the EPR signal intensity.…”

“…The addition of NO gas to an anaerobic solution of FeFur resulted in immediate change from colorless to yellow-green, associated to the appearance of absorption bands in the UV-visible spectra as well as a g ϭ 2.03 EPR signal. Both features are characteristics of NO-iron complexes (34)(35)(36)(37)(38). The rate of NO complex formation was controlled by the decomposition of DEANO (t 1/2 ϭ 15 min at 20°C, pH 7.5).…”

The interaction between sulfathiazole and cobalt(II): potentiometric studies

“…This purpose is very important in chemical, biochemical, biological, environmental and industrial fields [6][7][8] . For example, Co(II) and other metal complexes play an important role in the industrial cleaning of gaseous effluents from power plants through the suggested simultaneous absorption of nitric oxide and sulfur dioxide [9][10][11] . Furthermore, the binding, transport and activation of molecular oxygen by metal complexes is a topic of wide current interest due to the many implications that such metal containing systems have in both biomimetic and abiotic processes involving dioxygen 12 .…”