![]() 2D model of the tetrafluoroammonium ion
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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nitrogen atom have been replaced by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]
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]
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]
The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride at 120 °C: [5]
The reaction of nitrogen trifluoride with fluorine and boron trifluoride at 800 °C yields the tetrafluoroborate salt: [6]
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.
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]
Reaction of NF+
4SbF−
6 with
alkali metal nitrates yields
fluorine nitrate, FONO
2.
[4]
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]
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]
![]() 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]
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]
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]
The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride at 120 °C: [5]
The reaction of nitrogen trifluoride with fluorine and boron trifluoride at 800 °C yields the tetrafluoroborate salt: [6]
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.
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]
Reaction of NF+
4SbF−
6 with
alkali metal nitrates yields
fluorine nitrate, FONO
2.
[4]
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]
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]