Cobalt(II) bromide

Structure of cobalt(II) bromide tetrahydrate

Crystal structure of cobalt(II) bromide

Anhydrous cobalt(II) bromide in a vial
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.242
EC Number
  • 232-166-7
RTECS number
  • GF9595000
UNII
UN number 3077
  • InChI=1S/2BrH.Co/h2*1H;/q;;+2/p-2 checkY
    Key: BZRRQSJJPUGBAA-UHFFFAOYSA-L checkY
  • InChI=1/2BrH.Co/h2*1H;/q;;+2/p-2
    Key: BZRRQSJJPUGBAA-NUQVWONBAJ
  • [Co](Br)Br
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
+13000·10−6 cm3/mol
Structure
Rhombohedral, hP3, SpaceGroup = P-3m1, No. 164
octahedral
Hazards
GHS labelling:
GHS07: Exclamation markGHS08: Health hazardGHS09: Environmental hazard
Danger
H302, H312, H315, H317, H319, H332, H334, H335, H350
P201, P202, P261, P264, P270, P271, P272, P280, P281, P285, P301+P312, P302+P352, P304+P312, P304+P340, P304+P341, P305+P351+P338, P308+P313, P312, P321, P322, P330, P332+P313, P333+P313, P337+P313, P342+P311, P362, P363, P403+P233, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
2
0
1
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
406 mg/kg (oral, rat)
Safety data sheet (SDS) Fisher Scientific
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.

Properties

When anhydrous, cobalt(II) bromide appears as green crystals. It is hygroscopic and eventually 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.

The tetrahydrate is molecular, with the formula trans-[CoBr2(H2O)4].[4]

Preparation and reactions

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

Co(OH)2 + 2HBr → CoBr2·6H2O

The classical coordination compound bromopentaamminecobalt(III) bromide is prepared by oxidation of an aqueous solution of cobalt(II) bromide and ammonia.[5]

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.[6] Bromide is also mildly toxic.

References

  1. ↑ Perry, Dale L. (2011). Handbook of Inorganic Compounds (2nd ed.). Boca Raton: Taylor & Francis. p. 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. ↑ Waizumi, Kenji; Masuda, Hideki; Ohtaki, Hitoshi (1992). "X-ray Structural Studies of FeBr2·4H2O, CoBr2·4H2O, NiCl2·4H2O and CuBr2·4H2O. Cis/Trans Selectivity in Transition Metal(II) Dihalide Tetrahydrate". Inorganica Chimica Acta. 192 (2): 173–181. doi:10.1016/S0020-1693(00)80756-2.
  5. ↑ Diehl, Harvey; Clark, Helen; Willard, H. H.; Bailar, John C. (1939). "Bromopentamminocobalti Bromide". Inorganic Syntheses. Inorganic Syntheses. Vol. 1. p. 186. doi:10.1002/9780470132326.ch66. ISBN 978-0-470-13232-6.
  6. ↑ "Cobalt Bromide (OUS)" (PDF). Archived from the original (PDF) on 2007-06-25. Retrieved 2008-04-10.
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