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Cobalt(III) fluoride
Names
	Other names Cobalt trifluoride; Cobaltic fluoride; Cobalt fluoride; Cobaltic trifluoride
Identifiers
CAS Number	10026-18-3 ; 54496-71-8 dihydrate;
3D model (JSmol)	Interactive image;
ChemSpider	59593 ;
ECHA InfoCard	100.030.045
EC Number	233-062-4;
PubChem CID	66208;
UNII	O3R680UKNX ;
CompTox Dashboard (EPA)	DTXSID1064908 ;
	InChI InChI=1S/Co.3FH/h;31H/q+3;;;/p-3 Key: WZJQNLGQTOCWDS-UHFFFAOYSA-K ; InChI=1/Co.3FH/h;31H/q+3;;;/p-3 Key: WZJQNLGQTOCWDS-DFZHHIFOAL;
	SMILES F[Co](F)F;
Properties
Chemical formula	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)
Solubility in water	reacts
Magnetic susceptibility (χ)	+1900.0·10−6 cm3/mol
Structure
Crystal structure	hexagonal
Hazards
NFPA 704 (fire diamond)	3 0 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). verify (what is ?) Infobox references

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

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 CoF₃·3.5H₂O is known. It is conjectured to be better described as [CoF₃(H₂O)₃]·0.5H₂O.^[3]

There is a report of an hydrate CoF₃·3.5H₂O, isomorphic to AlF₃·3H₂O.^[3]

Preparation

Cobalt trifluoride can be prepared in the laboratory by treating CoCl₂ with fluorine at 250 °C:^[4]^[3]

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.^[3]

The compound can also be formed by treating CoCl₂ with chlorine trifluoride ClF₃ or bromine trifluoride BrF₃.^[3]

Reactions

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 agent. Used 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.^[5]

Gaseous CoF₃

In the gas phase, CoF₃ is calculated to be planar in its ground state, and has a 3-fold rotation axis (point group D_3h). 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

^ ^a ^b Coe, P. L. (2004). "Cobalt(III) Fluoride". Encyclopedia of Reagents for Organic Synthesis. J. Wiley. doi:10.1002/047084289X.rc185. ISBN 0471936235.
^ 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
^ ^a ^b ^c ^d ^e ^f 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
^ H. F. Priest (1950): "Anhydrous Metal Fluorides". In Inorganic Syntheses, McGraw-Hill, volume 3, pages 171-183. doi:10.1002/9780470132340.ch47
^ 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.
^ Yates, J. H.; Pitzer, R. M. (1979). "Molecular and Electronic Structure of Transition Metal Trifluorides". J. Chem. Phys. 70 (9): 4049–4055. Bibcode:1979JChPh..70.4049Y. doi:10.1063/1.438027.