Chromyl fluoride

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Chromyl fluoride
Chromyl-fluoride-2D.svg
Names
IUPAC name
Difluoro(dioxo)chromium
Other names
Chromyl Fluoride, Chromium Difluoride Dioxide
Identifiers
3D model (JSmol)
ChemSpider
EC Number
  • 232-137-9
PubChem CID
UNII
  • InChI=1S/Cr.2FH.2O/h;2*1H;;/q+2;;;;/p-2 X mark.svgN
    Key: FRLBLFFATGQISB-UHFFFAOYSA-L X mark.svgN
  • InChI=1/Cr.2FH.2O/h;2*1H;;/q+2;;;;/p-2/rCrF2O2/c2-1(3,4)5
    Key: FRLBLFFATGQISB-UNDMLHRZAG
  • O=[Cr](=O)(F)F
Properties
CrO2F2
Molar mass 121.991 g·mol−1
AppearanceViolet-red crystals
Melting point 31.6 °C (88.9 °F; 304.8 K)
Boiling point 30 °C (86 °F; 303 K) [1] Sublimes
Structure
monoclinic
P21/c, No. 14
C2v
4
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Oxidant
Related compounds
Related compounds
 chromyl chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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. [2]

Contents

Structure

The liquid and gaseous CrO2F2 have a tetrahedral geometry with C2v symmetry, much like chromyl chloride. [3] Chromyl fluoride dimerizes via fluoride bridges (as O2Cr(μ-F)4CrO2) in the solid state, crystallizing in the P21/c space group with Z = 4. The Cr=O bond lengths are about 157  pm, and the Cr–F bond lengths are 181.7, 186.7, and 209.4 pm. Chromium resides in a distorted octahedral position with a coordination number of 6. [4]

History and preparation

Pure chromyl fluoride was first isolated in 1952 as reported by Alfred Engelbrecht and Aristid von Grosse. [5] It was first observed as red vapor in the early 19th century upon heating a mixture of fluorspar (CaF2), chromates, and sulfuric acid. These red vapors were initially thought to be CrF6, although some chemists assumed a CrO2F2 structure analogous to CrO2Cl2. [5] The first moderately successful synthesis of chromyl fluoride was reported by Fredenhagen who examined the reaction of hydrogen fluoride with alkali chromates. A later attempt saw von Wartenberg prepare impure CrO2F2 by treating chromyl chloride with elemental fluorine. [6] Another attempt was made by Wiechert, who treated HF with dichromate, yielding impure liquid CrO2F2 at −40 °C.

Engelbrecht and von Grosse's synthesis of CrO2F2, and most successive syntheses, involve treating chromium trioxide with a fluorinating agent: [5]

CrO3 + 2 HF → CrO2F2 + H2O

The reaction is reversible, as water will readily hydrolyze CrO2F2 back to CrO3.

The approach published by Georg Brauer in the Handbook of Preparative Inorganic Chemistry [1] drew on von Wartenberg's approach [6] of direct fluoridation:

CrO2Cl2 + F2 → CrO2F2 + Cl2

Other methods include treatment with chlorine fluoride, carbonyl fluoride, or some metal hexafluorides:

CrO3 + 2 ClF → CrO2F2 + Cl2 + O2
CrO3 + COF2 → CrO2F2 + CO2
CrO3 + MF6 → CrO2F2 + MOF4 (M = Mo, W)

The last method involving the fluorides of tungsten and molybdenum are reported by Green and Gard to be very simple and effective routes to large quantities of pure CrO2F2. [2] They reported 100% yield when the reactions were conducted at 120 °C. As expected from the relative reactivities of MoF6 and WF6, the molybdenum reaction proceeded more readily than did the tungsten. [7]

Reactions

Chromyl fluoride is a strong oxidizing agent capable of converting hydrocarbons to ketones and carboxylic acids. It can also be used as a reagent in the preparation of other chromyl compounds. [2] Like some other fluoride compounds, CrO2F2 reacts with glass and quartz, so silicon-free plastics or metal containers are required for handling the compound. Its oxidizing power in inorganic systems has also been explored. [8] Chromyl fluoride can exchange fluorine atoms with metal oxides.

CrO2F2 + MO → MF2 + CrO3

Chromyl fluoride will also convert the oxides of boron and silicon to the fluorides. [8]

Chromyl fluoride reacts with alkali and alkaline earth metal fluorides in perfluoroheptane (solvent) to produce orange-colored fluorochromates: [8]

CrO2F2 + 2 MF → M2[CrO2F4]

Chromyl fluoride also reacts with Lewis acids, drawing carboxylate ligands from organic acid anhydrides and producing an acyl fluoride byproduct: [8]

CrO2F2 + 2 (CF3CO)2O → (CF3COO)2CrO2 + 2 CF3COF

Chromyl fluoride forms adducts with weak bases NO, NO2, and SO2.

Chromium oxytetrafluoride is prepared by fluorination of chromyl fluoride with krypton difluoride: [9]

CrO2F2 + KrF2 → CrOF4 + 0.5 O2 + Kr

Related Research Articles

Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.

<span class="mw-page-title-main">Oxygen fluoride</span> Any binary compound of oxygen and fluorine

Oxygen fluorides are compounds of elements oxygen and fluorine with the general formula OnF2, where n = 1 to 6. Many different oxygen fluorides are known:

<span class="mw-page-title-main">Copper(II) fluoride</span> Chemical compound

Copper(II) fluoride is an inorganic compound with the chemical formula CuF2. The anhydrous form is a white, ionic, crystalline, hygroscopic salt with a distorted rutile-type crystal structure, similar to other fluorides of chemical formulae MF2 (where M is a metal). The dihydrate, CuF2·2H2O, is blue in colour.

<span class="mw-page-title-main">Chromyl chloride</span> Chemical compound

Chromyl chloride is an inorganic compound with the formula CrO2Cl2. It is a reddish brown compound that is a volatile liquid at room temperature, which is unusual for transition metal compounds.

<span class="mw-page-title-main">Xenon difluoride</span> Chemical compound

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.

<span class="mw-page-title-main">Selenium tetrafluoride</span> Chemical compound

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.

<span class="mw-page-title-main">Chromium compounds</span> Chemical compounds containing chromium

Chromium compounds are compounds containing the element chromium (Cr). Chromium is a member of group 6 of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.

<span class="mw-page-title-main">Dioxygenyl</span> Chemical compound

The dioxygenyl ion, O+
2, is a rarely-encountered oxycation in which both oxygen atoms have a formal oxidation state of +1/2. It is formally derived from oxygen by the removal of an electron:

<span class="mw-page-title-main">Manganese(IV) fluoride</span> Chemical compound

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.

A hexafluoride is a chemical compound with the general formula QXnF6, QXnF6m−, or QXnF6m+. Many molecules fit this formula. An important hexafluoride is hexafluorosilicic acid (H2SiF6), which is a byproduct of the mining of phosphate rock. In the nuclear industry, uranium hexafluoride (UF6) is an important intermediate in the purification of this element.

In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula AOmXn, where X is a halogen. Known oxohalides have fluorine (F), chlorine (Cl), bromine (Br), and/or iodine (I) in their molecules. The element A may be a main group element, a transition element, a rare earth element or an actinide. The term oxohalide, or oxyhalide, may also refer to minerals and other crystalline substances with the same overall chemical formula, but having an ionic structure.

<span class="mw-page-title-main">Chromium(II) fluoride</span> Chemical compound

Chromium(II) fluoride is an inorganic compound with the formula CrF2. It exists as a blue-green iridescent solid. Chromium(II) fluoride is sparingly soluble in water, almost insoluble in alcohol, and is soluble in boiling hydrochloric acid, but is not attacked by hot distilled sulfuric acid or nitric acid. Like other chromous compounds, chromium(II) fluoride is oxidized to chromium(III) oxide in air.

<span class="mw-page-title-main">Neptunium(VI) fluoride</span> Chemical compound

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.

<span class="mw-page-title-main">Difluorophosphate</span> Chemical compound

Difluorophosphate or difluorodioxophosphate or phosphorodifluoridate is an anion with formula PO2F−2. It has a single negative charge and resembles perchlorate and monofluorosulfonate 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.

<span class="mw-page-title-main">Fluorocarbonate</span> Class of chemical compounds

A carbonate fluoride, fluoride carbonate, fluorocarbonate or fluocarbonate is a double salt containing both carbonate and fluoride. The salts are usually insoluble in water, and can have more than one kind of metal cation to make more complex compounds. Rare-earth fluorocarbonates are particularly important as ore minerals for the light rare-earth elements lanthanum, cerium and neodymium. Bastnäsite is the most important source of these elements. Other artificial compounds are under investigation as non-linear optical materials and for transparency in the ultraviolet, with effects over a dozen times greater than Potassium dideuterium phosphate.

<span class="mw-page-title-main">Radon compounds</span>

Radon compounds are chemical compounds formed by the element radon (Rn). Radon is a noble gas, i.e. a zero-valence element, and is chemically not very reactive. The 3.8-day half-life of radon-222 makes it useful in physical sciences as a natural tracer. Because radon is a gas under normal circumstances, and its decay-chain parents are not, it can readily be extracted from them for research.

Dioxygen monofluoride is a binary inorganic compound radical of fluorine and oxygen with the chemical formula O2F. The compound is stable only at low temperature. This is one of many known oxygen fluorides.

Hexaoxygen difluoride is a binary inorganic compound of fluorine and oxygen with the chemical formula O6F2. The compound is one of many known oxygen fluorides.

Chromium oxytetrafluoride is the inorganic compound with the formula CrOF4. It is a purple, volatile, diamagnetic solid. The compound is classified as an oxyfluoride. It can be prepared by fluorination of chromyl fluoride with krypton difluoride:

References

  1. 1 2 Brauer, Georg (1963) [1960]. "Chromyl Fluoride –CrO
    2    F
    2    "    . Handbook of Preparative Inorganic Chemistry, Volume 1 (2nd ed.). Stuttgart; New York: Ferdinand Enke Verlag; Academic Press, Inc. pp. 258–259. ISBN   978-0-32316127-5.
  2. 1 2 3 Gard, G. L. (1986) "Chromium Difluoride Dioxide (Chromyl Fluoride)," Inorg. Synth. , 24, 67-69, doi : 10.1002/9780470132555.ch20.
  3. ↑ Hobbs, W. E. (1958) "Infrared Absorption Spectra of Chromyl Fluoride and Chromyl Chloride," J. Chem. Phys. 28(6), 1220-1222, doi : 10.1063/1.1744372.
  4. ↑ Supeł, J.; Abram, U.; Hagenbach, A.; Seppelt, K. (2007) "Technetium Fluoride Trioxide, TcO3F, Preparation and Properties." Inorg. Chem. , 46(14), 5591–5595, doi : 10.1021/ic070333y.
  5. 1 2 3 Engelbrecht, A.; von Grosse, A. (1952) "Pure Chromyl Fluoride," J. Am. Chem. Soc. 74(21), 5262–5264, doi : 10.1021/ja01141a007.
  6. 1 2 von Wartenberg, H. (1941) "Über höhere Chromfluoride (CrF
    4    , CrF
    5     und CrO
    2    F
    2    )" [About higher chromium fluorides (CrF
    4    , CrF
    5     and CrO
    2    F
    2    )], Z. Anorg. Allg. Chem. [in German], 247(1-2), 135–146, doi : 10.1002/zaac.19412470112.
  7. ↑ Green, P. J.; Gard, G. L. (1977) "Chemistry of Chromyl Fluoride. 5. New Preparative routes to CrO2F2," Inorg. Chem. 16(5), 1243–1245, doi : 10.1021/ic50171a055.
  8. 1 2 3 4 Brown, S. D.; Green, P.J.; Gard, G.L. (1975) "The Chemistry of Chromyl Fluoride III: Reactions with Inorganic Systems," J. Fluorine Chem. 5(3), 203-219, doi : 10.1016/S0022-1139(00)82482-3.
  9. ↑ Christe, Karl O.; Wilson, William W.; Bougon, Roland A. (1986). "Synthesis and characterization of CrF4O, KrF2.CrF4O, and NO+CrF5O-". Inorganic Chemistry. 25 (13): 2163–2169. doi:10.1021/ic00233a013.
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