Chemistry:Cobalt(II) bromide

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Cobalt(II) bromide
Crystal structure of cobalt(II) bromide
Cobalt(II) bromide.jpg
Anhydrous cobalt(II) bromide in a vial
3D model (JSmol)
EC Number
  • 232-166-7
RTECS number
  • GF9595000
UN number 3077
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)
66.7 g/100 mL (59 °C)
68.1 g/100 mL (97 °C)
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
+13000·10−6 cm3/mol
Rhombohedral, hP3, SpaceGroup = P-3m1, No. 164
Safety data sheet Fisher Scientific
GHS pictograms GHS07: HarmfulGHS08: Health hazardGHS09: Environmental hazard
GHS Signal word Danger
H302, H312, H315, H317, H319, H332, H334, H335, H350
P201, P202, P261, P264, P270, P271, P272, P280, P281, P285, P301+312, P302+352, P304+312, P304+340, P304+341, P305+351+338, P308+313, P312, P321, P322, P330, P332+313, P333+313, P337+313, P342+311
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
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).
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Infobox references

Cobalt(II) bromide (CoBr2) is an inorganic compound. In its anhydrous form, it is a green solid that is soluble in water, used primarily as a catalyst in some processes.


When anhydrous, cobalt(II) bromide appears as green crystals. It is hygroscopic and forms the hexahydrate in air,[1] which appears as red-purple crystals. The hexahydrate loses four water 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.[2][3] At higher temperatures, cobalt(II) bromide reacts with oxygen, forming cobalt(II,III) oxide and bromine vapor.


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)

Reactions and uses

The classical coordination compound bromopentaamminecobalt(III) bromide is prepared by oxidation of a solution of cobalt(II) bromide in aqueous ammonia.[4]

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.


Exposure to large amounts of cobalt(II) can cause cobalt poisoning.[5] Bromide is also mildly toxic.


  1. Perry, Dale L. (2011). Handbook of Inorganic Compounds (2nd ed.). Boca Raton: Taylor & Francis. pp. 130. ISBN 978-1-4398-1461-1. OCLC 587104373. 
  2. Cobalt Bromide Supplier & Tech Info American Elements
  3. WebElements Periodic Table of the Elements
  4. Diehl, Harvey; Clark, Helen; Willard, H. H.; Bailar, John C. (1939). "Bromopentamminocobalti Bromide". Inorganic Syntheses. Inorganic Syntheses. 1. pp. 186. doi:10.1002/9780470132326.ch66. ISBN 978-0-470-13232-6. 
  5. "Archived copy".