Cobalt(II) bromide

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Cobalt(II) bromide
Identifiers
CAS number7789-43-7 YesY
PubChem24610
ChemSpider23012 YesY
RTECS numberGF9595000
Jmol-3D imagesImage 1
Properties
Molecular formulaCoBr2, CoBr2.6H2O, CoBr2.2H2O
Molar mass218.7412 g/mol (anhydrous)
326.74 g/mol (hexahydrate)
AppearanceBright green crystals (anhydrous)
Red-purple crystals (hexahydrate)
Density4.909 g/cm3 (anhydrous)
2.46 g/cm3 (hexahydrate)
Melting point678 °C (anhydrous)
47 °C (hexahydrate)
Solubility in wateranhydrous:
66.7 g/100 mL (59 °C)
68.1 g/100 mL (97 °C)
hexahydrate:
113.2 g/100 mL (20 °C)
Solubility77.1 g/100 mL (ethanol, 20 °C)
58.6 g/100 mL (methanol, 30 °C)
soluble in methyl acetate, ether, alcohol, acetone
Structure
Crystal structureRhombohedral, hP3, SpaceGroup = P-3m1, No. 164
Coordination
geometry
octahedral
Hazards
MSDSFisher Scientific
EU IndexNot listed
R-phrasesR36, R37, R38
S-phrasesS26, S37, S39, S45, S28A
NFPA 704
NFPA 704.svg
0
2
1
Flash pointNon-flammable
LD50406 mg/kg (oral, rat)
Related compounds
Other anionscobalt(II) fluoride
cobalt(II) chloride
cobalt(II) iodide
Other cationsiron(II) bromide
nickel(II) bromide
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C or 77 °F, 100 kPa)
Infobox references
 
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Cobalt(II) bromide
Identifiers
CAS number7789-43-7 YesY
PubChem24610
ChemSpider23012 YesY
RTECS numberGF9595000
Jmol-3D imagesImage 1
Properties
Molecular formulaCoBr2, CoBr2.6H2O, CoBr2.2H2O
Molar mass218.7412 g/mol (anhydrous)
326.74 g/mol (hexahydrate)
AppearanceBright green crystals (anhydrous)
Red-purple crystals (hexahydrate)
Density4.909 g/cm3 (anhydrous)
2.46 g/cm3 (hexahydrate)
Melting point678 °C (anhydrous)
47 °C (hexahydrate)
Solubility in wateranhydrous:
66.7 g/100 mL (59 °C)
68.1 g/100 mL (97 °C)
hexahydrate:
113.2 g/100 mL (20 °C)
Solubility77.1 g/100 mL (ethanol, 20 °C)
58.6 g/100 mL (methanol, 30 °C)
soluble in methyl acetate, ether, alcohol, acetone
Structure
Crystal structureRhombohedral, hP3, SpaceGroup = P-3m1, No. 164
Coordination
geometry
octahedral
Hazards
MSDSFisher Scientific
EU IndexNot listed
R-phrasesR36, R37, R38
S-phrasesS26, S37, S39, S45, S28A
NFPA 704
NFPA 704.svg
0
2
1
Flash pointNon-flammable
LD50406 mg/kg (oral, rat)
Related compounds
Other anionscobalt(II) fluoride
cobalt(II) chloride
cobalt(II) iodide
Other cationsiron(II) bromide
nickel(II) bromide
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C or 77 °F, 100 kPa)
Infobox references

Cobalt(II) bromide (CoBr2) is an inorganic compound. It is a red solid that is soluble in water, used primarily as a catalyst in some processes.

Properties[edit]

When anhydrous, cobalt(II) bromide appears as green crystals. The hexahydrate loses four waters of crystallization molecules at 100 °C forming the dihydrate:

CoBr2.6H2O → CoBr2.2H2O + 4 H2O

Further heating to 130 °C produces the anhydrous form:

CoBr2.4H2O → CoBr2

The anhydrous form melts at 678 °C.[1][2] At higher temperatures, cobalt(II) bromide reacts with oxygen, forming cobalt(II,III) oxide and bromine vapor.

Preparation[edit]

Cobalt(II) bromide can be prepared as a hydrate by the reaction of cobalt hydroxide with hydrobromic acid:

Co(OH)2(s) + 2HBr(aq) → CoBr2.6H2O(aq)

Anhydrous cobalt(II) bromide may be prepared through the direct reaction of elemental cobalt and liquid bromine.[3][4][5]

Reactions and uses[edit]

The classical coordination compound bromopentaamminecobalt(III) bromide is prepared by oxidation of a solution of cobalt(II) bromide in aqueous ammonia.[6]

2 CoBr2 + 8 NH3 + 2 NH4Br + H2O2 → 2 [Co(NH3)5Br]Br2 + 2 H2O

Triphenylphosphine complexes of cobalt(II) bromide have been used as a catalysts in organic synthesis.

Safety[edit]

Exposure to large amounts of cobalt(II) can cause cobalt poisoning.[7] Bromide is also mildly toxic.

References[edit]