Cobalt(II) bromide

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Cobalt(II) bromide
Cadmium-iodide-3D-layers.png
Identifiers
CAS number 7789-43-7 YesY
PubChem 24610
ChemSpider 23012 YesY
RTECS number GF9595000
Jmol-3D images Image 1
Properties
Molecular formula CoBr2, CoBr2.6H2O, CoBr2.2H2O
Molar mass 218.7412 g/mol (anhydrous)
326.74 g/mol (hexahydrate)
Appearance Bright green crystals (anhydrous)
Red-purple crystals (hexahydrate)
Density 4.909 g/cm3 (anhydrous)
2.46 g/cm3 (hexahydrate)
Melting point 678 °C (anhydrous)
47 °C (hexahydrate)
Solubility in water anhydrous:
66.7 g/100 mL (59 °C)
68.1 g/100 mL (97 °C)
hexahydrate:
113.2 g/100 mL (20 °C)
Solubility 77.1 g/100 mL (ethanol, 20 °C)
58.6 g/100 mL (methanol, 30 °C)
soluble in methyl acetate, ether, alcohol, acetone
Structure
Crystal structure Rhombohedral, hP3, SpaceGroup = P-3m1, No. 164
Coordination
geometry
octahedral
Hazards
MSDS Fisher Scientific
EU Index Not listed
R-phrases R36, R37, R38
S-phrases S26, S37, S39, S45, S28A
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
LD50 406 mg/kg (oral, rat)
Related compounds
Other anions cobalt(II) fluoride
cobalt(II) chloride
cobalt(II) iodide
Other cations iron(II) bromide
nickel(II) bromide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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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]