Nitryl fluoride is a colourless gas and strong oxidizing agent, which is used as a fluorinating agent and has been proposed as an oxidiser in rocket propellants (though never flown). Its formula is NO<sub>2</sub>F.
It is a molecular species, not ionic, consistent with its low boiling point. The structure features planar nitrogen with a short N-F bond length of 135 pm.
Henri Moissan and Paul Lebeau recorded the preparation of nitryl fluoride in 1905 by the fluorination of nitrogen dioxide. This reaction is highly exothermic, which leads to contaminated products. The simplest method avoids fluorine gas but uses cobalt(III) fluoride:
The CoF<sub>2</sub> can be regenerated to CoF<sub>3</sub>. Other methods have been described.
The thermodynamic properties of this gas were determined by IR and Raman spectroscopy. The standard heat of formation of FNO<sub>2</sub> is âÂÂ19 ñ 2 kcal/mol, but the compound becomes increasingly unstable at higher temperature. The homogeneous thermal decomposition cannot be studied at temperatures below 1200 kelvin, because the notional unimolecular decomposition equilibrium lies on the adduct side by at least six orders of magnitude at 500 kelvin, and two orders of magnitude at 1000 kelvin.
The dissociation energy of 46.0 kcal of the N-F bond in nitryl fluoride is about 18 kcal less than the normal N-F single bond energy. This can be attributed to the âÂÂreorganization energyâ of the NO<sub>2</sub> radical; that is, the NO<sub>2</sub> radical in FNO<sub>2</sub> is less stable than the free NO<sub>2</sub> molecule. Qualitatively speaking, the odd electron âÂÂused upâ in the N-F bond forms a resonating three-electron bond in free NO<sub>2</sub>, thus stabilizing the molecule with a gain of 18 kcal.
Nitryl fluoride can be used to prepare organic nitro compounds and nitrate esters.