Cobalt(III) fluoride

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

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
CoF
3
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 (fire diamond)
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. white phosphorusSpecial hazards (white): no code
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).
N verify (what is YN ?)
Infobox references

The related cobalt(III) chloride is also known but is extremely unstable.[2] Cobalt(III) bromide and cobalt(III) iodide have not been synthesized.

Structure

Anhydrous

Anhydrous cobalt trifluoride crystallizes in the rhombohedral group, specifically according to the aluminium trifluoride motif, with a = 527.9 pm, α = 56.97°. Each cobalt atom is bound to six fluorine atoms in octahedral geometry, with Co–F distances of 189 pm. Each fluoride is a doubly bridging ligand.[3]

Hydrates

A hydrate CoF
3·3.5H2O is known. It is conjectured to be better described as [CoF
3(H
2O)
3]·0.5H2O.[3]

There is a report of an hydrate CoF
3·3.5H2O, isomorphic to AlF
3·3H2O.[3]

Preparation

Cobalt trifluoride can be prepared in the laboratory by treating CoCl
2 with fluorine at 250 °C:[4][3]

CoCl
2 + 3/2 F
2 → CoF
3 + Cl
2

In this redox reaction, Co2+ and Cl− are oxidized to Co3+ and Cl
2, respectively, while F
2 is reduced to F−. Cobalt(II) oxide (CoO) and cobalt(II) fluoride (CoF
2) can also be converted to cobalt(III) fluoride using fluorine.[3]

The compound can also be formed by treating CoCl
2 with chlorine trifluoride ClF
3 or bromine trifluoride BrF
3.[3]

Reactions

CoF
3 decomposes upon contact with water to give oxygen:

4 CoF
3 + 2 H2O → 4 HF + 4 CoF
2 + O2

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


Applications

CoF
3 is a powerful fluorinating agent. Used as slurry, CoF
3 converts hydrocarbons to the perfluorocarbons:

2 CoF
3 + R-H → 2 CoF
2 + R-F + HF

CoF
2 is the byproduct.

Such reactions are sometimes accompanied by rearrangements or other reactions.[1] The related reagent KCoF4 is more selective.[5]

Gaseous CoF
3

In the gas phase, CoF
3 is calculated to be planar in its ground state, and has a 3-fold rotation axis (symmetry notation D3h). The Co3+ 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.[6] This calculation was the first treatment of the Jahn-Teller Effect using calculated energy surfaces.

References
  1. Coe, P. L. (2004). "Cobalt(III) Fluoride". Encyclopedia of Reagents for Organic Synthesis. J. Wiley. doi:10.1002/047084289X.rc185. ISBN 0471936235.
  2. Arthur W. Chester, El-Ahmadi Heiba, Ralph M. Dessau, and William J. Koehl Jr. (1969): "The interaction of cobalt(III) with chloride ion in acetic acid". Inorganic and Nuclear Chemistry Letters, volume 5, issue 4, pages 277-283. doi:10.1016/0020-1650(69)80198-4
  3. W. Levason and C. A. McAuliffe (1974): "Higher oxidation state chemistry of iron, cobalt, and nickel". Coordination Chemistry Reviews, volume 12, issue 2, pages 151-184. doi:10.1016/S0010-8545(00)82026-3
  4. H. F. Priest (1950): "Anhydrous Metal Fluorides". In Inorganic Syntheses, McGraw-Hill, volume 3, pages 171-183. doi:10.1002/9780470132340.ch47
  5. 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.
  6. 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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