Cobalt(III) fluoride
Template:Chembox Cobalt(III) fluoride is the inorganic compound with the formula Template:Chem2. 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 Template:Chem2 is known. It is conjectured to be better described as Template:Chem2.[3]
There is a report of an hydrate Template:Chem2, isomorphic to Template:Chem2.[3]
Preparation
Cobalt trifluoride can be prepared in the laboratory by treating [[cobalt(II) chloride|Template:Chem2]] with fluorine at 250 °C:[4][3]
In this redox reaction, Template:Chem2 and Template:Chem2 are oxidized to Template:Chem2 and Template:Chem2, respectively, while Template:Chem2 is reduced to Template:Chem2. Cobalt(II) oxide (CoO) and cobalt(II) fluoride (Template:Chem2) can also be converted to cobalt(III) fluoride using fluorine.[3]
The compound can also be formed by treating Template:Chem2 with chlorine trifluoride Template:Chem2 or bromine trifluoride Template:Chem2.[3]
Reactions
Template:Chem2 decomposes upon contact with water to give oxygen:
- 4 Template:Chem2 + 2 H2O → 4 HF + 4 CoTemplate:Chem2 + O2
It reacts with fluoride salts to give the anion [CoF6]3−, which is also features high-spin, octahedral cobalt(III) center.
Applications
Template:Chem2 is a powerful fluorinating agent. Used as slurry, Template:Chem2 converts hydrocarbons to the perfluorocarbons:
- 2 Template:Chem2 + R-H → 2 CoTemplate:Chem2 + R-F + HF
[[Cobalt(II) fluoride|CoTemplate:Chem2]] is the byproduct.
Such reactions are sometimes accompanied by rearrangements or other reactions.[1] The related reagent KCoF4 is more selective.[5]
Gaseous Template:Chem2
In the gas phase, Template:Chem2 is calculated to be planar in its ground state, and has a 3-fold rotation axis (point group D3h). The Template:Chem2 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 Script error: No such module "citation/CS1".
- ↑ 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. Script error: No such module "doi".
- ↑ 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. Script error: No such module "doi".
- ↑ H. F. Priest (1950): "Anhydrous Metal Fluorides". In Inorganic Syntheses, McGraw-Hill, volume 3, pages 171-183. Script error: No such module "doi".
- ↑ Coe, P. L. "Potassium Tetrafluorocobaltate(III)" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. Script error: No such module "doi"..
- ↑ Script error: No such module "Citation/CS1".