Dinitrogen difluoride

Dinitrogen difluoride^[1]

cis-Dinitrogen difluoride (left) and trans-dinitrogen difluoride (right)
Names
IUPAC name cis- or trans-dinitrogen difluoride
Other names cis- or trans-difluorodiazene
Identifiers
CAS Number	13812-43-6 (cis)
3D model (Jmol)	(cis): Interactive image
ChemSpider	10326121 (cis)
InChI (cis): InChI=1S/F2N2/c1-3-4-2/b4-3- Key: DUQAODNTUBJRGF-ONEGZZNKBY InChI=1S/F2N2/c1-3-4-2/b4-3+ Key: DUQAODNTUBJRGF-ARJAWSKDSA-N
SMILES (cis): F\N=N\F
Identifiers
CAS Number	13776-62-0 (trans)
3D model (Jmol)	(trans): Interactive image
ChemSpider	4516471 (trans)
InChI (trans): InChI=1/F2N2/c1-3-4-2/b4-3+ Key: DUQAODNTUBJRGF-ONEGZZNKBY InChI=1S/F2N2/c1-3-4-2/b4-3+ Key: DUQAODNTUBJRGF-ONEGZZNKSA-N
SMILES (trans): F\N=N/F
Properties
Chemical formula	N2F2
Molar mass	66.010 g/mol
Appearance	colorless gas
Density	2.698 g/L
Melting point	cis: < −195 °C (−319.0 °F; 78.1 K) trans: −172 °C
Boiling point	cis: −105.75 °C (−158.35 °F; 167.40 K) trans: −111.45 °C
Dipole moment	cis: 0.16 D trans: 0 D
Thermochemistry
Std enthalpy of formation (ΔfH^o298)	cis: 69.5 kJ/mol trans: 82.0 kJ/mol
Related compounds
Other cations	azo compounds diazene
Related Binary fluoro-azanes	nitrogen trifluoride tetrafluorohydrazine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Dinitrogen difluoride is a chemical compound with the formula N₂F₂. It is a gas at room temperature, and was first identified in 1952 as the thermal decomposition product of the azide N₃F. It has the structure F−N=N−F and exists in both a cis- and trans-form. The cis configuration lies in a C_2v symmetry and the trans-form has a symmetry of C_2h. These isomers are thermally interconvertible but can be separated by low temperature fractionation. The trans-form is less thermodynamically stable but can be stored in glass vessels. The cis-form attacks glass over a time scale of about 2 weeks to form silicon tetrafluoride and nitrous oxide:^[2]

2 N₂F₂ + SiO₂ → SiF₄ + 2 N₂O

Most preparations of dinitrogen difluoride give mixtures of the two isomers, but they can be prepared independently.

An aqueous method involves N,N-difluorourea with concentrated potassium hydroxide. This gives a 40% yield with three times more of the trans isomer.^[3]

Difluoramine forms a solid unstable compound with potassium fluoride (or rubidium fluoride or caesium fluoride) which decomposes to dinitrogen difluoride.^[3]

The cis form of dinitrogen difluoride will react with strong fluoride ion acceptors such as antimony pentafluoride to form the N₂F⁺ cation.

N₂F₂ + SbF₅ → N₂F⁺[SbF₆]⁻

In the solid phase, the observed N=N and N−F bond distances in the N₂F⁺ cation are 1.089(9) and 1.257(8) Å respectively, among the shortest experimentally observed N−N and N−F bonds.

References

1. Lide, David R. (1998). Handbook of Chemistry and Physics (87th ed.). Boca Raton, FL: CRC Press. pp. 4–73, 5–15, 9–46. ISBN 0-8493-0594-2.
2. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
3. Sykes, A. G. (1989-07-17). Advances in Inorganic Chemistry. Academic Press. p. 171. ISBN 9780080578828. Retrieved 21 June 2014.