Tetrafluoroammonium
Encyclopedia
The tetrafluoroammonium cation
(also known as perfluoroammonium) is a positively-charged polyatomic ion with chemical formula
. It is equivalent to the ammonium
ion where the hydrogen
atoms surrounding the central nitrogen
atom have been replaced by fluorine
.. Tetrafluoroammonium ion is isoelectronic
with tetrafluoromethane
and tetrafluoroborate
ion.
The tetrafluoroammonium ion forms salts with a large variety of fluorine-bearing anions. These include the bifluoride anion , tetrafluorobromate , metal pentafluorides ( where X is Ge
, Sn
, or Ti
), hexafluorides ( where X is P
, As
, Sb
, Bi
, or Pt
), heptafluorides ( where X is W
, U
, or Xe
), octafluorides , various oxyfluorides ( where X is W or U; ), and perchlorate
. Attempts to make the nitrate
salt, , were unsuccessful because of quick fluorination: + → + .
, with an estimated nitrogen-fluorine bond length of 124 pm
. All fluorine atoms are in equivalent positions.
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:
The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride
at 120 °C:
The reaction of nitrogen trifluoride with fluorine and boron trifluoride
at 800 °C yields the tetrafluoroborate salt:
salts can also be prepared by fluorination of with krypton difluoride
and fluorides of the form , where M is Sb, Nb, Pt, Ti, or B. For example, reaction of with and yields .
Many tetrafluoroammonium salts can be prepared with methatesis reactions. More information: http://books.google.hu/books?id=xLP_KevavOkC&lpg=PA47&ots=f2nv-FsKKs&dq=tetrafluoroammonium&pg=PA39#v=onepage&q&f=false.
into nitrogen trifluoride, , and oxygen
gas:
Some hydrogen peroxide
is also formed during this process.
Reaction of with alkali metal
nitrates yields fluorine nitrate, .
of aromatic compounds in organic chemistry
.
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
(also known as perfluoroammonium) is a positively-charged polyatomic ion with chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
. It is equivalent to the ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
ion where the hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
atoms surrounding the central nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atom have been replaced by fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
.. Tetrafluoroammonium ion is isoelectronic
Isoelectronicity
Two or more molecular entities are described as being isoelectronic with each other if they have the same number of electrons or a similar electron configuration and the same structure , regardless of the nature of the elements involved.The term valence isoelectronic is used when these molecular...
with tetrafluoromethane
Tetrafluoromethane
Tetrafluoromethane, also known as carbon tetrafluoride, is the simplest fluorocarbon . It has a very high bond strength due to the nature of the carbon–fluorine bond. It can also be classified as a haloalkane or halomethane...
and tetrafluoroborate
Tetrafluoroborate
Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4−...
ion.
The tetrafluoroammonium ion forms salts with a large variety of fluorine-bearing anions. These include the bifluoride anion , tetrafluorobromate , metal pentafluorides ( where X is Ge
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
, Sn
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
, or Ti
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
), hexafluorides ( where X is P
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, As
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, Sb
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
, Bi
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
, or Pt
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
), heptafluorides ( where X is W
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
, U
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, or Xe
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
), octafluorides , various oxyfluorides ( where X is W or U; ), and perchlorate
Perchlorate
Perchlorates are the salts derived from perchloric acid . They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate is also a...
. Attempts to make the nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
salt, , were unsuccessful because of quick fluorination: + → + .
Structure
The geometry of the tetrafluoroammonium ion is tetrahedralTetrahedral molecular geometry
In a tetrahedral molecular geometry a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1 ≈ 109.5° when all four substituents are the same, as in CH4. This molecular geometry is common throughout the first...
, with an estimated nitrogen-fluorine bond length of 124 pm
Picometre
A picometre is a unit of length in the metric system, equal to one trillionth, i.e. of a metre, which is the current SI base unit of length...
. All fluorine atoms are in equivalent positions.
Synthesis
Tetrafluoroammonium salts are prepared by oxidising nitrogen trifluorideNitrogen trifluoride
Nitrogen trifluoride is the inorganic compound with the formula NF3. This nitrogen-fluorine compound is a colorless, toxic, odourless, nonflammable gas. It finds increasing use as an etchant in microelectronics.-Applications:...
with fluorine
Fluorine
Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
in the presence of a strong Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
which acts as a fluoride
Fluoride
Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...
ion acceptor. The original synthesis by Tolberg, Rewick, Stringham, and Hill in 1966 employs antimony pentafluoride
Antimony pentafluoride
Antimony pentafluoride is the inorganic compound with the formula SbF5. This colourless, viscous liquid is a valuable Lewis acid and a component of the superacid fluoroantimonic acid, the strongest known acid...
as the Lewis acid:
- + + →
The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride
Arsenic pentafluoride
Arsenic pentafluoride is a chemical compound of arsenic and fluorine. The oxidation state of arsenic is +5.-Synthesis:Arsenic pentafluoride can be prepared by direct combination of arsenic and fluorine:...
at 120 °C:
- + + →
The reaction of nitrogen trifluoride with fluorine and boron trifluoride
Boron trifluoride
Boron trifluoride is the chemical compound with the formula BF3. This pungent colourless toxic gas forms white fumes in moist air. It is a useful Lewis acid and a versatile building block for other boron compounds.-Structure and bonding:...
at 800 °C yields the tetrafluoroborate salt:
- + + →
salts can also be prepared by fluorination of with krypton difluoride
Krypton difluoride
Krypton difluoride, KrF2, was the first compound of krypton discovered. It is a volatile, colourless solid. The structure of the KrF2 molecule is linear, with Kr−F distances of 188.9 pm...
and fluorides of the form , where M is Sb, Nb, Pt, Ti, or B. For example, reaction of with and yields .
Many tetrafluoroammonium salts can be prepared with methatesis reactions. More information: http://books.google.hu/books?id=xLP_KevavOkC&lpg=PA47&ots=f2nv-FsKKs&dq=tetrafluoroammonium&pg=PA39#v=onepage&q&f=false.
Reactions
Tetrafluoroammonium salts are extremely hygroscopic. The ion is readily hydrolysedHydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
into nitrogen trifluoride, , and oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
gas:
- 2 + 2 → 2 + 2 +
Some hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
is also formed during this process.
Reaction of with alkali metal
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
nitrates yields fluorine nitrate, .
Applications
salts are important for solid propellant gas generators. They are also used as reagents for electrophilic fluorinationElectrophilic fluorination
Electrophilic fluorination is the combination of a carbon-centered nucleophile with an electrophilic source of fluorine to afford organofluorine compounds...
of aromatic compounds in organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
.