Cobalt(II) bromide

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.

Cobalt(II) bromide

Anhydrous cobalt(II) bromide in a vial
Identifiers
CAS Number
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.242
EC Number
  • 232-166-7
PubChem CID
RTECS number
  • GF9595000
UNII
UN number 3077
CompTox Dashboard (EPA)
Properties
Chemical 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 (1,252 °F; 951 K) (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
Magnetic susceptibility (χ)
 +13000·10−6 cm3/mol
Structure
Crystal structure
 Rhombohedral, hP3, SpaceGroup = P-3m1, No. 164
Coordination geometry
 octahedral
Hazards
Safety data sheet Fisher Scientific
GHS pictograms
GHS Signal word Danger
GHS hazard statements
 H302, H312, H315, H317, H319, H332, H334, H335, H350
GHS precautionary statements
 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)
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).
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Infobox references

Properties

When anhydrous, cobalt(II) bromide appears as green crystals, while the hexahydrate appears as red-purple 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 Archived 2008-02-19 at the Wayback Machine
  5. Pilgaard Solutions: Cobalt Archived 2009-01-22 at the Wayback Machine
  6. Diehl, Harvey; Clark, Helen; Willard, H. H.; Bailar, John C. (1939). "Bromopentamminocobalti Bromide". Inorganic Syntheses. Inorganic Syntheses. 1. p. 186. doi:10.1002/9780470132326.ch66. ISBN 978-0-470-13232-6.
  7. "Archived copy" (PDF). Archived from the original (PDF) on 2007-06-25. Retrieved 2008-04-10.CS1 maint: archived copy as title (link)