Nitroso

Nitroso refers to a functional group in organic chemistry which has the NO group attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds (e.g., nitrosoalkanes; R-N=O), S-nitroso compounds (nitrosothiols; RS-N=O), N-nitroso compounds (e.g., nitrosamines, R¹N(-R²)-N=O), and O-nitroso compounds (alkyl nitrites; RO-N=O).

Nitrosyls are non-organic compounds containing the NO group, for example directly bound to the metal via the N-atom, giving a metal-NO moiety. Alternatively, a non-metal example is the common reagent nitrosyl chloride (Cl-N=O).

Nitric oxide is a stable radical, having an unpaired electron.

Reduction of nitric oxide gives the hyponitrite anion, NO⁻:

Oxidation of NO yields the nitrosonium cation, NO⁺:

Nitrosyl as a ligand

Nitric oxide can serve as a ligand in complexes. The resulting complexes are called metal nitrosyls, and can bond to a metal atom in two extreme modes: as NO⁺ and as NO⁻. It is generally assumed that NO⁺ coordinates linearly, the M−N−O angle being 180°, whereas NO⁻ forms a bent geometry, with an M−N−O angle of approximately 120°. However, the results of many studies have shown that the ionic descriptions of the NO ligand do not correlate with metal-NO geometry. A more realistic description of electron-counting in metal-nitrosyl chemistry is given by the Enemark-Feltham notation.