Dinitrogen difluoride

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.

Dinitrogen difluoride[1]

cis-Dinitrogen difluoride (left) and trans-dinitrogen difluoride (right)
Cis-dinitrogen difluoride molecule
Trans-dinitrogen difluoride molecule
Names
IUPAC name
cis- or trans-dinitrogen difluoride
Other names
cis- or trans-difluorodiazene
Identifiers
3D model (JSmol)
ChemSpider
Properties
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
cis: 0.16 D
trans: 0 D
Thermochemistry
Std enthalpy of
formation (ΔfH⦵298)
 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).
N verify (what is YN ?)
Infobox references

Isomers

The cis configuration lies in a C2v symmetry and the trans-form has a symmetry of C2h. 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

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.[3]

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

It can also be prepared by photolysis of tetrafluorohydrazine and bromine:[4]

Reactions

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 978-0-08-037941-8.
  3. Sykes, A. G. (1989-07-17). Advances in Inorganic Chemistry. Academic Press. p. 171. ISBN 9780080578828. Retrieved 21 June 2014.
  4. Leon M. Zaborowski; et al. (1973), Aaron Wold and John K. Ruff (ed.), "Chlorodifluoroamine and Difluorodiazene - B. Difluorodiazene (Dinitrogen difluoride)", Inorganic Syntheses (in German), McGraw-Hill Book Company, Inc., 14, pp. 34–39
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