Metal/metallic nitrosyls nitric oxide

Keywords Metal-Nitrosyls, Metal-Peroxo, Metal-Superoxo, Nitric Oxide Dioxygenation References ... 

Carbonyl Nitric Oxides. Another group of metal-carbonyl complexes, worthy of investigation as CVD precursors, consists of the carbonyl nitric oxides. In these complexes, one (or more) CO group is replaced by NO. An example is cobalt nitrosyl tricarbonyl, CoNO(CO)3, which is a preferred precursor for the CVD of cobalt. It is a liquid with a boiling point of 78.6°C which decomposes at 66°C. It is prepared by passing NO through an aqueous solution of cobalt nitrate and potassium cyanide and potassium hydroxide. ... 

Ford, P.C., Bourassa, J., Miranda, K. et al. (1998) Photochemistry of metal nitrosyl complexes. Delivery of nitric oxide to biological targets, Coord. Chem. Rev., 171, 185. 

Lead(II) oxide Non-metals Lead(IV) oxide Non-metals Nitric acid Non-metals Nitrogen oxide Non-metals Nitrosyl fluoride Metals, etc. Nitryl fluoride Non-metals Oxygen difluoride Non-metals Potassium nitrite Boron Potassium nitrate Non-metals Silver difluoride Boron, etc. Sodium peroxide Non-metals... 

Fe(CN)5(NO)] makes several appearances in a recent symposium volume dedicated to nitric oxide in biosystems, for example in cormection with iron(II) dtrate-induced oxidative stress." " Nitroprusside is the only metal nitrosyl complex in clinical use, where it is important as a rapidly acting agent for the lowering of exceptionally high blood pressure. ... 

Nitric oxide rapidly reacts with transition metals, which have stable oxidation states differing by one electron (see Chapters 2 and 3). Nitric oxide is unusual in that it reacts with both the ferric (Fe " ) and ferrous forms (Fe " ) of iron. TTie unpaired electron of nitric oxide is partially transferred to the metal forming a principally ionic bond. Complexes of ferric iron with nitric oxide are called nitrosyl compounds and will nitrosate (add an NO group) many compounds, while reducing the iron to the ferrous state (Wade and Castro, 1990). 

There are at least three mechanisms for the reversal of NO inhibition of an enzyme. The most obvious is that the NO can be released as the concentration of NO in solution falls or the temperature rises. This depends on the (kinetic) off constant for NO in the system in question as well as the (equilibrium) dissociation constant for most enzymes that form nitrosyl complexes, this has not been measured. Nitric oxide bound to a metal center could also undergo oxidation or reduction followed by the release of product. Finally, NO could be photodissociated from a metal center by light of the correct wavelength. 

A description involving two extreme bonding formulations is currently used to explain the nature of the M—N—O linkage in most mononuclear complexes. In the sense of formal oxidation state it is now customary to think of linear nitrosyls as derived from NO+ and bent (120°) nitrosyls as derived from NO-.23,24 Bond formation between free nitric oxide and a transition metal ion must then be considered to involve either prior donation of an electron from NO (giving NO+) or prior acceptance of an electron by NO (giving NO-) 25 in each case this would of course be followed by lone pair donation from the nitrogen. Using this somewhat simplistic view it is easy to explain the... 

It is possible that nitric oxide may be displaced from the metal centre prior to oxidation of the phosphine. Indeed, such a nitrosyl displacement in the complex CrCl(7t-Cp)(NO)2, leading to derivatives of the type CrCl(jr-Cp)NO(L), has been reported.118 However, such behaviour is rare (compared with CO displacements in metal carbonyls) and it seems likely that the above reduction takes place by an alternative process. 

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