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Cobalt(II) bromide

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Title: Cobalt(II) bromide  
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Subject: Cobalt(II) iodide, Metal aquo complex, Cobalt(II) hydroxide, Cobalt, Cobalt(II) chlorate
Collection: Bromides, Cobalt Compounds, Metal Halides
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Cobalt(II) bromide

Cobalt(II) bromide
Identifiers
 YesY
ChemSpider  YesY
Jmol-3D images Image
PubChem
RTECS number GF9595000
Properties
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 (1,252 °F; 951 K) (anhydrous)
47 °C (hexahydrate)
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
Rhombohedral, hP3, SpaceGroup = P-3m1, No. 164
octahedral
Hazards
Safety data sheet Fisher Scientific
R-phrases R36, R37, R38
S-phrases S26, S37, S39, S45, S28A
NFPA 704
0
2
1
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
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 otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 YesY  (: YesY/N?)

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.

Contents

  • Properties 1
  • Preparation 2
  • Reactions and uses 3
  • Safety 4
  • References 5

Properties

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:

CoBr2.2H2O → CoBr2 + 2 H2O

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

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

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

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

References

  1. ^ Cobalt Bromide Supplier & Tech Info American Elements
  2. ^ WebElements Periodic Table of the Elements
  3. ^ WebElements Periodic Table of the Elements | Cobalt | Essential information
  4. ^ Chemical Properties and Reaction Tendencies
  5. ^ Pilgaard Solutions: Cobalt
  6. ^
  7. ^ http://www.chrismanual.com/C/COB.pdf
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