Tetrafluoroammonium
 2D model of the tetrafluoroammonium ion
| |
| Names | |
|---|---|
| IUPAC name
Tetrafluoroammonium
| |
| Identifiers | |
3D model (JSmol)
|
|
| ChEBI | |
| ChemSpider | |
| 2028 | |
PubChem CID
|
|
CompTox Dashboard (EPA)
|
|
| |
| |
| Properties | |
| F4N | |
| Molar mass | 90.000 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
The tetrafluoroammonium cation (also known as perfluoroammonium) is a positively charged polyatomic ion with chemical formula NF
4. It is equivalent to the ammonium ion where the hydrogen atoms surrounding the central nitrogen atom have been replaced by fluorine.[1] Tetrafluoroammonium ion is isoelectronic with tetrafluoromethane CF
4, trifluoramine oxide ONF
3, tetrafluoroborate BF−
4 anion and the tetrafluoroberyllate BeF2−
4 anion.
The tetrafluoroammonium ion forms salts with a large variety of fluorine-bearing anions. These include the bifluoride anion (HF−
2), tetrafluorobromate (BrF−
4), metal pentafluorides (MF−
5 where M is Ge, Sn, or Ti), hexafluorides (MF−
6 where M is P, As, Sb, Bi, or Pt), heptafluorides (MF−
7 where M is W, U, or Xe), octafluorides (XeF2−
8),[2] various oxyfluorides (MF
5O−
where M is W or U; FSO−
3, BrF
4O−
), and perchlorate (ClO−
4).[3] Attempts to make the nitrate salt, NF
4NO
3, were unsuccessful because of quick fluorination: NF
4 NO−
3 → NF
3 FONO
2.[4]
Structure
[edit]The geometry of the tetrafluoroammonium ion is tetrahedral, with an estimated nitrogen-fluorine bond length of 124 pm. All fluorine atoms are in equivalent positions.[5]
Synthesis
[edit]Tetrafluoroammonium salts are prepared by oxidising nitrogen trifluoride with fluorine in the presence of a strong Lewis acid which acts as a fluoride ion acceptor. The original synthesis by Tolberg, Rewick, Stringham, and Hill in 1966 employs antimony pentafluoride as the Lewis acid:[5]
- NF
3 F
2 SbF
5 → NF
4SbF
6
The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride at 120 °C:[5]
- NF
3 F
2 AsF
5 → NF
4AsF
6
The reaction of nitrogen trifluoride with fluorine and boron trifluoride at 800 °C yields the tetrafluoroborate salt:[6]
- NF
3 F
2 BF
3 → NF
4BF
4
NF
4 salts can also be prepared by fluorination of NF
3 with krypton difluoride (KrF
2) and fluorides of the form MF
n, where M is Sb, Nb, Pt, Ti, or B. For example, reaction of NF
3 with KrF
2 and TiF
4 yields [NF
4]
2TiF2−
6.[7]
Many tetrafluoroammonium salts can be prepared with metathesis reactions.
Reactions
[edit]Tetrafluoroammonium salts are extremely hygroscopic. The NF
4 ion, when dissolved in water, readily decomposes into NF
3, H
2F
, and oxygen gas. Some hydrogen peroxide (H
2O
2) is also formed during this process:[5]
- NF
4 H
2O → NF
3 H
2F
1⁄2 O
2
- NF
4 2 H
2O → NF
3 H
2F
H
2O
2
Reaction of NF
4SbF−
6 with alkali metal nitrates yields fluorine nitrate, FONO
2.[4]
Properties
[edit]Because NF
4 salts are destroyed by water, water cannot be used as a solvent. Instead, bromine trifluoride, bromine pentafluoride, iodine pentafluoride, or anhydrous hydrogen fluoride can be used.[8]
Tetrafluoroammonium salts usually have no colour. However, some are coloured due to other elements in them. (NF
4)
2CrF2−
6, (NF
4)
2NiF2−
6 and (NF
4)
2PtF2−
6 have a red colour, while (NF
4)
2MnF2−
6, NF
4UF−
7, NF
4UOF−
5 and NF
4XeF−
7 are yellow.[8]
Applications
[edit]NF
4 salts are important for solid propellant NF
3–F
2 gas generators. They are also used as reagents for electrophilic fluorination of aromatic compounds in organic chemistry.[5] As fluorinating agents, they are also strong enough to react with methane.[9]
See also
[edit]References
[edit]- ^ Nikitin, I. V.; Rosolovskii, V. Y. (1985). "Tetrafluoroammonium Salts". Russian Chemical Reviews. 54 (5): 426. Bibcode:1985RuCRv..54..426N. doi:10.1070/RC1985v054n05ABEH003068. S2CID 250864362.
- ^ Christe, K. O.; Wilson, W. W. (1982). "Perfluoroammonium and alkali-metal salts of the heptafluoroxenon(VI) and octafluoroxenon(VI) anions". Inorganic Chemistry. 21 (12): 4113–4117. doi:10.1021/ic00142a001.
- ^ Christe, K. O.; Wilson, W. W. (1986). "Synthesis and characterization of tetrafluoroammonium(1 ) tetrafluorobromate(1-) and tetrafluoroammonium(1 ) tetrafluorooxobromate(1-)". Inorganic Chemistry. 25 (11): 1904–1906. doi:10.1021/ic00231a038.
- ^ a b Hoge, B.; Christe, K. O. (2001). "On the stability of NF
4NO−
3 and a new synthesis of fluorine nitrate". Journal of Fluorine Chemistry. 110 (2): 87–88. doi:10.1016/S0022-1139(01)00415-8.+
4NO−
3 and a new synthesis of fluorine nitrate&rft.volume=110&rft.issue=2&rft.pages=87-88&rft.date=2001&rft_id=info:doi/10.1016/S0022-1139(01)00415-8&rft.aulast=Hoge&rft.aufirst=B.&rft.au=Christe, K. O.&rfr_id=info:sid/en.wikipedia.org:Tetrafluoroammonium" class="Z3988"> - ^ a b c d e Sykes, A. G. (1989). Advances in Inorganic Chemistry. Academic Press. ISBN 0-12-023633-8.
- ^ Patnaik, Pradyot (2002). Handbook of inorganic chemicals. McGraw-Hill Professional. ISBN 0-07-049439-8.
- ^ John H. Holloway; Eric G. Hope (1998). A. G. Sykes (ed.). Advances in Inorganic Chemistry. Academic Press. pp. 60–61. ISBN 0-12-023646-X.
- ^ a b Sykes, A. G. (1989-07-17). Advances in Inorganic Chemistry. Academic Press. p. 154. ISBN 9780080578828. Retrieved 22 June 2014.
- ^ Olah, George A.; Hartz, Nikolai; Rasul, Golam; Wang, Qi; Prakash, G. K. Surya; Casanova, Joseph; Christe, Karl O. (1994-06-01). "Electrophilic Fluorination of Methane with "F " Equivalent N2F and NF4 Salts". Journal of the American Chemical Society. 116 (13): 5671–5673. doi:10.1021/ja00092a018. ISSN 0002-7863.