Names | |
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IUPAC name manganese tetrafluoride | |
Other names manganese(IV) fluoride | |
Identifiers | |
3D model (JSmol) | |
ChemSpider | |
PubChem CID | |
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Properties [1] [2] | |
MnF4 | |
Molar mass | 130.93 g mol−1 |
Appearance | blue solid |
Density | 3.61 g cm−3 (calc.) [3] |
Melting point | 70 °C (158 °F; 343 K) decomposes |
reacts violently | |
Structure | |
tetragonal, tI80 [3] [4] | |
I41/a (No. 88) [Note 1] | |
a = 1263 pm, c = 604.9 pm | |
Related compounds | |
Other cations | Manganese(II) fluoride Manganese(III) fluoride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Manganese tetrafluoride, MnF4, is the highest fluoride of manganese. It is a powerful oxidizing agent and is used as a means of purifying elemental fluorine. [2] [5]
Manganese tetrafluoride was first unequivocally prepared in 1961 [Note 2] by the reaction of manganese(II) fluoride (or other MnII compounds) with a stream of fluorine gas at 550 °C: the MnF4 sublimes into the gas stream and condenses onto a cold finger. [1] [7] This is still the commonest method of preparation, although the sublimation can be avoided by operating at increased fluorine pressure (4.5–6 bar at 180–320 °C) and mechanically agitating the powder to avoid sintering of the grains. [2] [8] The reaction can also be carried out starting from manganese powder in a fluidized bed. [9] [10]
Other preparations of MnF4 include the fluorination of MnF2 with krypton difluoride, [11] or with F2 in liquid hydrogen fluoride solution under ultraviolet light. [12] Manganese tetrafluoride has also been prepared (but not isolated) in an acid–base reaction between antimony pentafluoride and K2MnF6 as part of a chemical synthesis of elemental fluorine. [13]
Manganese tetrafluoride is in equilibrium with manganese(III) fluoride and elemental fluorine:
Decomposition is favoured by increasing temperature, and disfavoured by the presence of fluorine gas, but the exact parameters of the equilibrium are unclear, with some sources saying that MnF4 will decompose slowly at room temperature, [14] [15] others placing a practical lower temperature limit of 70 °C, [2] [16] and another claiming that MnF4 is essentially stable up to 320 °C. [17] The equilibrium pressure of fluorine above MnF4 at room temperature has been estimated at about 10−4 Pa (10−9 bar), and the enthalpy change of reaction at +44(8) kJ mol−1. [18] [Note 3]
Manganese tetrafluoride reacts violently with water and even with sodium-dried petroleum ether. It immediately decomposes on contact with moist air. [1]
Reaction with alkali metal fluorides or concentrated hydrofluoric acid gives the yellow hexafluoromanganate(IV) anion [MnF6]2−. [17]
The main application of manganese tetrafluoride is in the purification of elemental fluorine. Fluorine gas is produced by electrolysis of anhydrous hydrogen fluoride (with a small amount of potassium fluoride added as a support electrolyte) in a Moissan cell. The technical product is contaminated with HF, much of which can be removed by passing the gas over solid KF, but also with oxygen (from traces of water) and possibly heavy-metal fluorides such as arsenic pentafluoride (from contamination of the HF). These contaminants are particularly problematic for the semiconductor industry, which uses high-purity fluorine for etching silicon wafers. Further impurities, such as iron, nickel, gallium and tungsten compounds, can be introduced if unreacted fluorine is recycled. [5]
The technical-grade fluorine is purified by reacting it with MnF3 to form manganese tetrafluoride. As this stage, any heavy metals present will form involatile complex fluorides, while the HF and O2 are unreactive. Once the MnF3 has been converted, the excess gas is vented for recycling, carrying the remaining gaseous impurities with it. The MnF4 is then heated to 380 °C to release fluorine at purities of up to 99.95%, reforming MnF3, which can be reused. [2] [5] By placing two reactors in parallel, the purification process can be made continuous, with one reactor taking in technical fluorine while the other delivers high-grade fluorine. [5] Alternatively, the manganese tetrafluoride can be isolated and transported to where the fluorine is needed, at lower cost and greater safety than pressurized fluorine gas. [2] [8]
The yellow hexafluoromanganate(2−) of alkali metal and alkaline earth metal cations have been known since 1899, and can be prepared by the fluorination of MnF2 in the presence of the fluoride of the appropriate cation. [12] [20] [21] [22] They are much more stable than manganese tetrafluoride. [13] Potassium hexafluoromanganate(IV), K2MnF6, can also be prepared by the controlled reduction of potassium permanganate in 50% aqueous hydrofluoric acid. [23] [24]
The pentafluoromanganate(1−) salts of potassium, rubidium and caesium, MMnF5, can be prepared by fluorination of MMnF3 or by the reaction of [MnF4(py)(H2O)] with MF. [22] [24] The lemon-yellow heptafluoromanganate(3−) salts of the same metals, M3MnF7, have also been prepared. [25]
When potassium hexafluoromanganate is doped into potassium fluorosilicate it forms a narrow band red phosphor. [26]
Manganese(III) fluoride (also known as Manganese trifluoride) is the inorganic compound with the formula MnF3. This red/purplish solid is useful for converting hydrocarbons into fluorocarbons, i.e., it is a fluorination agent. It forms a hydrate and many derivatives.
Silver(II) fluoride is a chemical compound with the formula AgF2. It is a rare example of a silver(II) compound. Silver usually exists in its +1 oxidation state. It is used as a fluorinating agent.
Xenon difluoride is a powerful fluorinating agent with the chemical formula XeF
2, and one of the most stable xenon compounds. Like most covalent inorganic fluorides it is moisture-sensitive. It decomposes on contact with water vapor, but is otherwise stable in storage. Xenon difluoride is a dense, colourless crystalline solid.
Sulfur tetrafluoride is the chemical compound with the formula SF4. It is a colorless corrosive gas that releases dangerous HF upon exposure to water or moisture. Despite these unwelcome characteristics, this compound is a useful reagent for the preparation of organofluorine compounds, some of which are important in the pharmaceutical and specialty chemical industries.
Selenium tetrafluoride (SeF4) is an inorganic compound. It is a colourless liquid that reacts readily with water. It can be used as a fluorinating reagent in organic syntheses (fluorination of alcohols, carboxylic acids or carbonyl compounds) and has advantages over sulfur tetrafluoride in that milder conditions can be employed and it is a liquid rather than a gas.
Copper(I) fluoride or cuprous fluoride is an inorganic compound with the chemical formula CuF. Its existence is uncertain. It was reported in 1933 to have a sphalerite-type crystal structure. Modern textbooks state that CuF is not known, since fluorine is so electronegative that it will always oxidise copper to its +2 oxidation state. Complexes of CuF such as [(Ph3P)3CuF] are, however, known and well characterised.
Plutonium hexafluoride is the highest fluoride of plutonium, and is of interest for laser enrichment of plutonium, in particular for the production of pure plutonium-239 from irradiated uranium. This pure plutonium is needed to avoid premature ignition of low-mass nuclear weapon designs by neutrons produced by spontaneous fission of plutonium-240.
Palladium(II) fluoride, also known as palladium difluoride, is the chemical compound of palladium and fluorine with the formula PdF2.
Chromyl fluoride is an inorganic compound with the formula CrO2F2. It is a violet-red colored crystalline solid that melts to an orange-red liquid.
Vanadium(V) fluoride is the inorganic compound with the chemical formula VF5. It is a colorless volatile liquid. It is a highly reactive compound, as indicated by its ability to fluorinate organic substances.
Neptunium(VI) fluoride (NpF6) is the highest fluoride of neptunium, it is also one of seventeen known binary hexafluorides. It is an orange volatile crystalline solid. It is relatively hard to handle, being very corrosive, volatile and radioactive. Neptunium hexafluoride is stable in dry air but reacts vigorously with water.
Fluorine forms a great variety of chemical compounds, within which it always adopts an oxidation state of −1. With other atoms, fluorine forms either polar covalent bonds or ionic bonds. Most frequently, covalent bonds involving fluorine atoms are single bonds, although at least two examples of a higher order bond exist. Fluoride may act as a bridging ligand between two metals in some complex molecules. Molecules containing fluorine may also exhibit hydrogen bonding. Fluorine's chemistry includes inorganic compounds formed with hydrogen, metals, nonmetals, and even noble gases; as well as a diverse set of organic compounds. For many elements the highest known oxidation state can be achieved in a fluoride. For some elements this is achieved exclusively in a fluoride, for others exclusively in an oxide; and for still others the highest oxidation states of oxides and fluorides are always equal.
The global market for chemicals from fluorine was about US$16 billion per year as of 2006. The industry was predicted to reach 2.6 million metric tons per year by 2015. The largest market is the United States. Western Europe is the second largest. Asia Pacific is the fastest growing region of production. China in particular has experienced significant growth as a fluorochemical market and is becoming a producer of them as well. Fluorite mining was estimated in 2003 to be a $550 million industry, extracting 4.5 million tons per year.
Tetrafluoroberyllate or orthofluoroberyllateBeF2−
4 is an anion containing beryllium and fluorine. The fluoroanion has a tetrahedral shape, with the four fluorine atoms surrounding a central beryllium atom. It has the same size and outer electron structure as sulfate. Therefore, many compounds that contain sulfate have equivalents with tetrafluoroberyllate. Examples of these are the langbeinites, and Tutton's salts.
Difluorophosphate or difluorodioxophosphate or phosphorodifluoridate is an anion with formula PO
2F−
2. It has a single negative charge and resembles perchlorate (ClO−
4) and monofluorosulfonate (SO3F−) in shape and compounds. These ions are isoelectronic, along with tetrafluoroaluminate, phosphate, orthosilicate, and sulfate. It forms a series of compounds. The ion is toxic to mammals as it causes blockage to iodine uptake in the thyroid. However it is degraded in the body over several hours.
1,1,1,2-tetrafluorodisulfane, also known as 1,2-difluorodisulfane 1,1-difluoride or just difluorodisulfanedifluoride (FSSF3) is an unstable molecular compound of fluorine and sulfur. The molecule has a pair of sulfur atoms, with one fluorine atom on one sulfur, and three fluorine atoms on the other. It has the uncommon property that all the bond lengths are different. The bond strength is not correlated with bond length but is inversely correlated with the force constant (Badger's rule). The molecule can be considered as sulfur tetrafluoride in which a sulfur atom is inserted into a S-F bond.
1,3-Difluoro-trisulfane-1,1-difluoride is an inorganic molecular substance with the structure SF3SSF, consisting of sulfur in a low oxidation state with fluorine. The compound consists of a chain of three sulfur atoms, with three fluorine atoms bonded to the sulfur on one end and the fourth fluorine bonded to the sulfur on the other end. It has a melting point of -62 °C and a boiling point of 94 °C. As a gas, it is unstable and breaks up to form SSF2 and SF4.
Terbium(IV) fluoride is an inorganic compound with a chemical formula TbF4. It is a white solid that is a strong oxidizer. It is also a strong fluorinating agent, emitting relatively pure atomic fluorine when heated, rather than the mixture of fluoride vapors emitted from cobalt(III) fluoride or cerium(IV) fluoride. It can be produced by the reaction between very pure terbium(III) fluoride and xenon difluoride, chlorine trifluoride or fluorine gas:
The hexafluoroarsenate anion is a chemical species with formula AsF−6. Hexafluoroarsenate is relatively inert, being the conjugate base of the notional superacid hexafluoroarsenic acid.
Seleninyl fluoride is an oxyfluoride of selenium with the chemical formula SeOF2.