Nitrosonium
The nitrosonium ion is , in which the nitrogen atom is bonded to an oxygen atom with a bond order of 3, and the overall diatomic species bears a positive charge. It can be viewed as nitric oxide with one electron removed. This ion is usually obtained as the following salts: ,  (nitrosylsulfuric acid, more descriptively written ) and . The  and  salts are slightly soluble in acetonitrile . NOBF4 can be purified by sublimation at 200–250 °C and . Synthesis and spectroscopy
 is isoelectronic with CO,  and . It arises via protonation of nitrous acid:
HONO + H+  NO+ + H2O

In its infrared spectrum of its salts, νNO is a strong peak in the range 2150-2400 cm-1. Chemical properties

Hydrolysis
 reacts readily with water to form nitrous acid:

For this reason, nitrosonium compounds must be protected from water or even moist air. With base, the reaction generates nitrite:

As a diazotizing agent
 reacts with aryl amines, , to give diazonium salts, . The resulting diazonium group is easily displaced (unlike the amino group) by a variety of nucleophiles. As an oxidizing agent
, e.g. as , is a strong oxidizing agent:
 vs. ferrocene/ferrocenium,  in  solution has a redox potential of 1.00 V (or 1.46–1.48 V vs SCE),
 vs. ferrocene/ferrocenium,  in  solution has a redox potential of 0.87 V vs. (or 1.27–1.25 V vs SCE). is a convenient oxidant because the byproduct NO is a gas, which can be swept from the reaction using a stream of . Upon contact with air, NO forms , which can cause secondary reactions if it is not removed. is readily detectable by its characteristic orange color. Nitrosylation of arenes
Electron-rich arenes are nitrosylated using NOBF4. One example involves anisole:
 CH3OC6H5 + NOBF4 → CH3OC6H4NO + HBF4
Nitrosonium, , is sometimes confused with nitronium, NO, the active agent in nitrations. These species are quite different, however. Nitronium is a more potent electrophile than is nitrosonium, as anticipated by the fact that the former is derived from a strong acid (nitric acid) and the latter from a weak acid (nitrous acid). As a source of nitrosyl complexes

NOBF4 reacts with some metal carbonyl complexes to yield related metal nitrosyl complexes. In some cases, [NO]+ does not bind the metal nucleophile but acts as an oxidant. (C6Et6)Cr(CO)3 + NOBF4 → [(C6Et6)Cr(CO)2(NO)]BF4 + CO

See also
Nitronium (NO2+)
Nitric oxide (NO)

References

Oxycations
Nitrogen(III) compounds