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Chromyl fluoride

Names
IUPAC name Difluoro(dioxo)chromium
Other names Chromyl Fluoride, Chromium Difluoride Dioxide
Identifiers
CAS Number	7788-96-7
3D model (JSmol)	Interactive image
ChemSpider	10329781
EC Number	232-137-9
PubChem CID	53471881
UNII	UB519P5O68
InChI InChI=1S/Cr.2FH.2O/h;2*1H;;/q+2;;;;/p-2Key: FRLBLFFATGQISB-UHFFFAOYSA-L InChI=1/Cr.2FH.2O/h;2*1H;;/q+2;;;;/p-2/rCrF2O2/c2-1(3,4)5Key: FRLBLFFATGQISB-UNDMLHRZAG
SMILES O=(=O)(F)F
Properties
Chemical formula	CrO2F2
Molar mass	121.991 g·mol
Appearance	Violet-red crystals
Melting point	31.6 °C (88.9 °F; 304.8 K)
Boiling point	30 °C (86 °F; 303 K) Sublimes
Structure
Crystal structure	monoclinic
Space group	P21/c, No. 14
Point group	C2v
Formula units (Z)	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 , 100 kPa). N verify (what is  ?) Infobox references

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.

Structure

The liquid and gaseous CrO₂F₂ have a tetrahedral geometry with C_2v symmetry, much like chromyl chloride. 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.

History and preparation

Pure chromyl fluoride was first isolated in 1952 as reported by Alfred Engelbrecht and Aristid von Grosse. 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. 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. 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:

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 drew on von Wartenberg's approach 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. 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.

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. 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. 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.

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

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:

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:

CrO₂F₂ + KrF₂ → CrOF₄ + 0.5 O₂ + Kr

References

1. ^ Brauer, Georg (1963) . "Chromyl Fluoride – CrO
   ₂F
   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. ^ 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. ^ Engelbrecht, A.; von Grosse, A. (1952) "Pure Chromyl Fluoride," J. Am. Chem. Soc. 74(21), 5262–5264, doi:10.1021/ja01141a007.
6. ^ von Wartenberg, H. (1941) "Über höhere Chromfluoride (CrF
   ₄, CrF
   ₅ und CrO
   ₂F
   ₂)" , Z. Anorg. Allg. Chem. , 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. ^ 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.

• Chromium(VI) compounds
• Chromium–halogen compounds
• Oxidizing agents
• Oxyfluorides
• Chromium–oxygen compounds