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

Dinitrogen difluoride^[1]

cis-dinitrogen difluoride trans-dinitrogen difluoride
Names
IUPAC name cis- or trans-dinitrogen difluoride
Other names cis- or trans-difluorodiazene
Identifiers
CAS Number	13812-43-6 (cis) N 13776-62-0 (trans)
3D model (JSmol)	(cis): Interactive image (trans): Interactive image
ChemSpider	10326121 (cis) N 4516471 (trans) N
PubChem CID	5364290 (cis) 5462838 (trans)
InChI (cis): InChI=1S/F2N2/c1-3-4-2/b4-3- Key: DUQAODNTUBJRGF-ONEGZZNKBY (trans): InChI=1/F2N2/c1-3-4-2/b4-3+ Key: DUQAODNTUBJRGF-ONEGZZNKBY InChI=1S/F2N2/c1-3-4-2/b4-3+ Y Key: DUQAODNTUBJRGF-ARJAWSKDSA-N Y
SMILES (cis): F\N=N\F (trans): F\N=N/F
Properties
Chemical formula	FN=NF
Molar mass	66.011 g·mol−1
Appearance	Colorless gas
Density	2.698 g/L
Melting point	cis: less than −195 °C (−319.0 °F; 78.1 K) trans: −172 °C (−278 °F)
Boiling point	cis: −105.75 °C (−158.35 °F; 167.40 K) trans: −111.45 °C (−168.61 °F)
Dipole moment	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 anions	Azide
Other cations	Ammonium Diazonium compounds Pentazenium Tetrafluoroammonium
Related compounds	Azo compounds Diazene Triazene Tetrazene 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 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.^{[clarification needed]} The trans isomer is less thermodynamically stable^[2] 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:^{[3][page needed]}

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.^[4]

Difluoramine forms a solid unstable compound with potassium fluoride (or rubidium fluoride or caesium fluoride) which decomposes to dinitrogen difluoride.^[4]

It can also be prepared by photolysis of tetrafluorohydrazine and bromine:^[5]

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^[6] [N≡N−F]⁺ cation (fluorodiazonium cation^[6]) 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]^−[6] (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.