Nitronium
The nitronium ion is a cation with the formula (NO+
2).
Properties
It is stable enough to exist in normal conditions, but it is generally reactive and used extensively as an electrophile in the nitration of other substances.
Nitronium salts
A few stable nitronium salts with anions of weak nucleophilicity can be isolated. These include nitronium perchlorate (NO+
2ClO−
4), nitronium tetrafluoroborate (NO+
2BF−
4), nitronium hexafluorophosphate (NO+
2PF−
6), nitronium hexafluoroarsenate (NO+
2AsF−
6), and nitronium hexafluoroantimonate (NO+
2SbF−
6). These are all very hygroscopic compounds and readily hydrolyze in contact with water.
The solid form of dinitrogen pentoxide, N2O5, actually consists of nitronium and nitrate ions, so it is an ionic compound, [NO+
2][NO−
3], not a molecular solid. However, dinitrogen pentoxide in liquid or gaseous state is molecular and does not contain nitronium ions.
The compounds nitryl fluoride, NO2F, and nitryl chloride, NO2Cl, are not nitronium salts but molecular compounds, as shown by their low boiling points (−72 °C and −6 °C respectively) and short N–X bond lengths (N–F 135 pm, N–Cl 184 pm).
The related negatively charged species is NO−
2, the nitrite ion.
Nitrogen dioxide is not a nitronium compound.
