Cobalt(III) fluoride is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemi ...
with the formula .
Hydrates are also known. The anhydrous compound is a hygroscopic brown solid. It is used to synthesize
organofluorine compounds.
The related
cobalt(III) chloride is also known but is extremely unstable.
[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. ] Cobalt(III) bromide and cobalt(III) iodide have not been synthesized.
Structure
Anhydrous
Anhydrous cobalt trifluoride crystallizes in the
rhombohedral
In geometry, a rhombohedron (also called a rhombic hexahedron or, inaccurately, a rhomboid) is a three-dimensional figure with six faces which are rhombi. It is a special case of a parallelepiped where all edges are the same length. It can be use ...
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.
[
]
Hydrates
A hydrate is known. It is conjectured to be better described as .[
There is a report of an hydrate , isomorphic to .][
]
Preparation
Cobalt trifluoride can be prepared in the laboratory by treating with fluorine at 250 °C:[H. F. Priest (1950): "Anhydrous Metal Fluorides". In ''Inorganic Syntheses'', McGraw-Hill, volume 3, pages 171-183. ][
: + 3/2 → +
In this redox reaction, and are oxidized to and , respectively, while is reduced to . Cobalt(II) oxide (CoO) and cobalt(II) fluoride () can also be converted to cobalt(III) fluoride using fluorine.][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. ]
The compound can also be formed by treating with chlorine trifluoride or bromine trifluoride .[
]
Reactions
decomposes upon contact with water to give oxygen:
:4 + 2 H2O → 4 HF + 4 Co + O2
It reacts with fluoride salts to give the anion oF6sup>3−, which is also features high-spin, octahedral cobalt(III) center.
Applications
is a powerful fluorinating agent. Used as slurry, converts hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
s to the perfluorocarbons
Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commerci ...
:
:2 + R-H → 2 Co + R-F + HF
Co is the byproduct.
Such reactions are sometimes accompanied by rearrangements or other reactions.[ The related reagent KCoF4 is more selective.
]
Gaseous
In the gas phase, is calculated to be planar in its ground state, and has a 3-fold rotation axis (symmetry notation D3h). The 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.
References
External links
National Pollutant Inventory - Cobalt fact sheet
{{fluorine compounds
Fluorides
Metal halides
Cobalt(III) compounds
Fluorinating agents