Dinitrogen difluoride - Misplaced Pages

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 fluorine azide (FN₃). It has the structure F−N=N−F and exists in both cis and trans isomers, as typical for diimides.

Isomers

The cis isomer has C_2v symmetry and the trans isomer has C_2h symmetry. These isomers can interconvert, but the process is slow enough at low temperature that the two can separated by low-temperature fractionation. The trans isomer is less thermodynamically stable but can be stored in glass vessels. The cis isomer attacks glass over a time scale of about 2 weeks to form silicon tetrafluoride and nitrous oxide:

2 N₂F₂ + SiO₂ → SiF₄ + 2 N₂O

Preparation

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.

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

It can also be prepared by photolysis of tetrafluorohydrazine and bromine:

N₂F₄ hv→Br₂ N₂F₂ + byproducts

Reactions

The cis form of difluorodiazene will react with strong fluoride ion acceptors such as antimony pentafluoride to form the linear [N≡N−F] cation (fluorodiazonium cation) which forms a salt with the formula [N≡N−F][SbF₆] (fluorodiazonium hexafluoroantimonate(V)).

F−N=N−F + SbF₅ → [N≡N−F][SbF₆]

Analogous reaction of cis-difluorodiazene with arsenic pentafluoride gives white solid salt with the formula [N≡N−F][AsF₆] (fluorodiazonium hexafluoroarsenate(V)).

F−N=N−F + AsF₅ → [N≡N−F][AsF₆]

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

References

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.
Christe, Karl O.; Dixon, David A.; Grant, Daniel J.; Haiges, Ralf; Tham, Fook S.; Vij, Ashwani; Vij, Vandana; Wang, Tsang-Hsiu; Wilson, William W. (2010-08-02). "Dinitrogen Difluoride Chemistry. Improved Syntheses of cis - and trans -N 2 F 2 , Synthesis and Characterization of N 2 F + Sn 2 F 9 − , Ordered Crystal Structure of N 2 F + Sb 2 F 11 − , High-Level Electronic Structure Calculations of cis -N 2 F 2 , trans -N 2 F 2 , F 2 N═N, and N 2 F + , and Mechanism of the trans−cis Isomerization of N 2 F 2". Inorganic Chemistry. 49 (15): 6823–6833. doi:10.1021/ic100471s. ISSN 0020-1669. PMID 20465274.
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
^ Sykes, A. G. (1989-07-17). Advances in Inorganic Chemistry. Academic Press. p. 171. ISBN 9780080578828. Retrieved 21 June 2014.
Leon M. Zaborowski; et al. (1973), Aaron Wold and John K. Ruff (ed.), Chlorodifluoroamine and Difluorodiazene - B. Difluorodiazene (Dinitrogen difluoride), Inorganic Syntheses (in German), vol. 14, McGraw-Hill Book Company, Inc., pp. 34–39
^ Cacace, Fulvio; Grandinetti, Felice; Pepi, Federico (1995). "Gaseous Fluorodiazonium Ions. Experimental and Theoretical Study on Formation and Structure of FN2+". Inorganic Chemistry. 34 (6): 1325–1332. doi:10.1021/ic00110a007.

v t e Nitrogen species
Hydrides	NH₃ NH+4 NH−2 N NH₂OH N₂H₄ HN₃ N−3 NH₅ (?)
Organic	NR₃ >C=NR −CONR₂ −CN HCN CN (CN)₂ H₂NCN HOCN HNCO HNCS CH₂N₂ −NO −NO₂
Oxides	NO / (NO)₂ N₂O₃ HNO₂ / NO−2 / NO NO₂ / (NO₂)₂ N₂O₅ HNO₃ / NO−3 / NO+2 NO₃ HNO / (HON)₂ / N₂O−2 / N₂O H₂NNO₂ HO₂NO / ONOO HO₂NO₂ / O₂NOO NO−4 H₄N₂O₄ / N₂O2−3
Halides	NF NF₂ NF₃ NF₅ (?) NCl₃ NBr₃ NI₃ FN₃ ClN₃ BrN₃ IN₃ NH₂F N₂F₂ NH₂Cl NHF₂ NHCl₂ NHBr₂ NHI₂
Oxidation states	−3, −2, −1, 0, +1, +2, +3, +4, +5 (a strongly acidic oxide)

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