Dinitrogen difluoride

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

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

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) Ã… respectively, among the shortest experimentally observed N-N and N-F bonds.