Cobalt(II) fluoride

Cobalt(II) fluoride
IUPAC name Cobalt(II) fluoride
Other names cobalt difluoride
Identifiers
CAS number	10026-17-2 Y
PubChem	24820
ChemSpider	23205 Y
EC number	233-061-9
RTECS number	GG0770000
Jmol-3D images	Image 1
SMILES F[Co]F
InChI InChI=1S/Co.2FH/h;2*1H/q+2;;/p-2 Y Key: YCYBZKSMUPTWEE-UHFFFAOYSA-L Y InChI=1/Co.2FH/h;2*1H/q+2;;/p-2 Key: YCYBZKSMUPTWEE-NUQVWONBAL
Properties
Molecular formula	CoF2
Molar mass	96.93 g/mol
Appearance	Red crystalline solid
Density	4.46 g/cm3 (anhydrous) 2.22 g/cm3 (tetrahydrate)
Melting point	1217 °C, 1490 K, 2223 °F
Boiling point	1400 °C, 1673 K, 2552 °F
Solubility in water	1.4 g/100 mL (25 °C)
Solubility	soluble in HF insoluble in alcohol, ether, benzene
Structure
Crystal structure	tetragonal (a,hydrous) orthorhombic (tetrahydrate)
Hazards
NFPA 704	0 3 2
LD50	oral (rat): 150 mg/kg
Related compounds
Other anions	cobalt(II) oxide, cobalt(II) chloride
Other cations	iron(II) fluoride, nickel(II) fluoride
Related compounds	cobalt trifluoride
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Cobalt(II) fluoride is a chemical compound with the formula (CoF₂). It is a pink crystalline solid compound. The formula is given for both the red tetragonal crystal, (CoF₂), and the tetrahydrate red orthogonal crystal, (CoF₂ •4H₂O). CoF₂ is used in oxygen-sensitive fields, namely metal production. In low concentrations, it has public health uses. CoF₂ is sparingly soluble in water. The compound can be dissolved in warm mineral acid, and will decompose in boiling water. Yet the hydrate is water soluble, especially the di-hydrate CoF₂ •2H₂ O and tri-hydrate CoF₂ •3H₂O forms of the compound. The hydrate will also decompose with heat.

Preparation

Cobalt(II) fluoride can be prepared from anhydrous cobalt(II) chloride or cobalt(II) oxide in a stream of hydrogen fluoride:

CoCl₂ + 2HF → CoF₂ + 2HCl

CoO + 2HF → CoF₂ + H₂ O

It is produced in the reaction of cobalt (III) fluoride with water.

The tetrahydrate cobalt(II) fluoride is formed by dissolving cobalt(II) in hydrofluoric acid. The anhydrous fluoride can be extracted from this by dehydration. Other synthesis can occur at higher temperatures. It has been shown that at 500 °C fluorine will combine with cobalt producing a mixture of CoF₂ and CoF₃.

Uses

Cobalt(II) fluoride can be used as a catalyst to alloy metals. It is also used for optical deposition, of which it tremendously improves optical quality. Cobalt(II) fluoride is available in most volumes in an ultra high purity composition. High purity compositions improve optical qualities and its usefulness as a standard. The compound may be used in dental care^{[citation needed]}, since fluoride is also used in dental care.

Analysis

To analyze this compound, Cobalt (II) fluoride can be dissolved in nitric acid. The solution is then diluted with water until appropriate concentration for AA or ICP spectrophotometry for the cobalt. A small amount of salt can be dissolved in cold water and analyzed for fluoride ion by a fluoride ion-selective electrode or ion chromatography.

Chemical Properties

CoF₂ is a weak Lewis acid. Cobalt(II) complexes are usually octahedral or tetrahedral. As a 19-electron species it is a good reducing agent, fairly oxidizable into an 18-electron compound. Cobalt(II) fluoride can be reduced by hydrogen at a 300 °C.

External links

• National Pollutant Inventory - Cobalt fact sheet
• National Pollutant Inventory - Fluoride and compounds fact sheet
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