Cobalt(III) fluoride

Cobalt(III) fluoride
Names
Other names
Cobalt trifluoride
Cobaltic fluoride
Cobalt fluoride
Cobaltic trifluoride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.045
EC Number 233-062-4
UNII
Properties
CoF3
Molar mass 115.928 g/mol
Appearance brown powder
Density 3.88 g/cm3
Melting point 927 °C (1,701 °F; 1,200 K)
reacts
+1900.0·10−6 cm3/mol
Structure
hexagonal
Hazards
NFPA 704
Flammability code 0: Will not burn. E.g., waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorusSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
3
2
Related compounds
Other anions
 cobalt(III) oxide, cobalt(III) chloride
Other cations
 iron(III) fluoride, rhodium(III) fluoride
Related compounds
 cobalt(II) fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cobalt(III) fluoride is the inorganic compound with the formula CoF3. A dihydrate is also known. The anhydrous compound is a hygroscopic brown solid. It is used to synthesize organofluorine compounds.[1]

Preparation

CoF3 is prepared in the laboratory by treating CoCl2 with fluorine at 250 °C:[2]

CoCl2 + 3/2 F2 → CoF3 + Cl2

In this redox reaction, Co2+ and Cl− are oxidized to Co3+ and Cl2, respectively, while F2 is reduced to F−. Cobalt(II) oxide (CoO) and cobalt(II) fluoride (CoF2) can also be converted to cobalt(III) fluoride using fluorine.

Structure and reactions

The compound crystallizes in the aluminium trifluoride motif. Each fluoride is a doubly bridging ligand. The cobalt centers are octahedral.

CoF3 decomposes upon contact with water to give oxygen:

4 CoF3 + 2 H2O → 4 HF + 4 CoF2 + O2

It reacts with fluoride salts to give the anion [CoF6]3−, which is also features high-spin, octahedral cobalt(III) center.

Applications

CoF3 is a powerful fluorinating agentUsed as slurry, CoF3 converts hydrocarbons to the perfluorocarbons:

2 CoF3 + R-H → 2 CoF2 + R-F + HF

CoF2 is the byproduct.

Such reactions are sometimes accompanied by rearrangements or other reactions.[1] The related reagent KCoF4 is more selective.[3]

Gaseous CoF3

In the gas phase, CoF3 is calculated to be planar in its ground state, and has a 3-fold rotation axis (symmetry notation D3h). The Cr3+ ion has a ground state of 3d6 5D. The fluoride ligands split this state into, in energy order, 5A', 5E", and 5E' states. The first energy difference is small and the 5E" state is subject to the Jahn-Teller Effect, so this effect needs to be considered to be sure of the ground state. The energy lowering is small and does not change the energy order.[4] This calculation was the first treatment of the Jahn-Teller Effect using calculated energy surfaces.

References

  1. 1 2 Coe, P. L. (2004). "Cobalt(III) Fluoride". Encyclopedia of Reagents for Organic Synthesis. J. Wiley. doi:10.1002/047084289X.rc185.
  2. ↑ Priest, H. F. "Anhydrous Metal Fluorides" Inorganic Syntheses McGraw-Hill: New York, 1950; Vol. 3, pages 171-183. doi:10.1002/9780470132340.ch47
  3. ↑ Coe, P. L. "Potassium Tetrafluorocobaltate(III)" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X.rp251.
  4. ↑ Yates, J. H.; Pitzer, R. M. (1979). "Molecular and Electronic Structure of Transition Metal Trifluorides". J. Chem. Phys. 70 (9): 4049–4055. doi:10.1063/1.438027.
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