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Cobalt(II) bromide

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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 InfoCard100.029.242Edit this at Wikidata
EC Number
  • 232-166-7
RTECS number
  • GF9595000
UNII
UN number3077
  • 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 mass218.7412 g/mol (anhydrous)
326.74 g/mol (hexahydrate)
AppearanceBright green crystals (anhydrous)
Red-purple crystals (hexahydrate)
Density4.909 g/cm3 (anhydrous)
2.46 g/cm3 (hexahydrate)
Melting point678 °C (1,252 °F; 951 K) (anhydrous)[1][2]
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)
Solubility77.1 g/100 mL (ethanol, 20 °C)
58.6 g/100 mL (methanol, 30 °C)
soluble inmethyl 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)
Flash pointNon-flammable
Lethal dose or concentration (LD, LC):
406 mg/kg (oral, rat)
Safety data sheet (SDS)Fisher Scientific
Related compounds
Otheranions
cobalt(II) fluoride
cobalt(II) chloride
cobalt(II) iodide
Othercations
iron(II) bromide
nickel(II) bromide
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa).
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Chemical compound

Cobalt(II) bromide refers toinorganic compounds with the formulaCoBr2·(H2O)n. The anhydrous form (n = 0) is a green solid and the hexahydrate (n = 6) is a red solid.[3] These compounds find some use ascatalysts.[4]

Structure

[edit]

The anhydrous compound has acadmium iodide structure. The tetrahydrate is molecular, with the formulatrans-[CoBr2(H2O)4].[5]

Preparation and reactions

[edit]

Cobalt(II) bromide form by treating an aqueous suspension ofcobalt(II) carbonate withhydrobromic acid according to the following idealized equation:[3]

CoCO3 + 2 HBr + 5 H2O → CoBr2(H2O)6 + CO2

Anhydrous cobalt(II) bromide ishygroscopic. Air exposure eventually forms the hexahydrate in air,[6] 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

The anhydrous compound forms by heating any of the hydrates to >150 °C in a vacuum:

CoBr2(H2O)6 → CoBr2 + 6 H2O

The resulting solid can be purified byvacuum sublimation at > 500 °C.[3]

Further heating to 130 °C produces the anhydrous form:

CoBr2·2H2O → CoBr2 + 2 H2O

At higher temperatures, cobalt(II) bromide reacts withoxygen, formingcobalt(II,III) oxide andbromine vapor.[citation needed]

Thecoordination compoundbromopentaamminecobalt(III) bromide is prepared by oxidation of an aqueous solution of cobalt(II) bromide and ammonia.[7]

2 CoBr2 + 8 NH3 + 2 NH4Br + H2O2 → 2 [Co(NH3)5Br]Br2 + 2 H2O

Triphenylphosphine complexes of cobalt(II) bromide have been used as acatalysts in organic synthesis.[8]

Safety

[edit]

Exposure to large amounts of cobalt(II) can causecobalt poisoning.[9] Bromide is also mildly toxic.

References

[edit]
  1. ^Cobalt Bromide Supplier & Tech InfoAmerican Elements
  2. ^WebElements Periodic Table of the Elements
  3. ^abcO. Glemser (1963). "Cobalt(II) bromide". In G. Brauer (ed.).Handbook of Preparative Inorganic Chemistry, 2nd Ed. Vol. 2. NY, NY: Academic Press. p. 1517.
  4. ^Le Gall, Erwan; Martens, Thierry (2012). "Multicomponent Synthesis of Tertiary Diarylmethylamines: 1-((4-Fluorophenyl)(4-methoxyphenyl)methyl)piperidine".Organic Syntheses.89: 283.doi:10.15227/orgsyn.089.0283.
  5. ^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.
  6. ^Perry, Dale L. (2011).Handbook of Inorganic Compounds (2nd ed.). Boca Raton: Taylor & Francis. p. 130.ISBN 978-1-4398-1461-1.OCLC 587104373.
  7. ^Diehl, Harvey; Clark, Helen; Willard, H. H.; Bailar, John C. (1939). "Bromopentamminocobalti Bromide".Inorganic Syntheses. Vol. 1. p. 186.doi:10.1002/9780470132326.ch66.ISBN 978-0-470-13232-6.{{cite book}}:ISBN / Date incompatibility (help)
  8. ^Gund, Tamara M.; Thielecke, Wilfried; R. Schleyer, Paul v. (1973). "Diamantane: Pentacyclo[7.3.1.14,12.02,7.06,11]Tetradecane".Organic Syntheses.53: 30.doi:10.15227/orgsyn.053.0030.
  9. ^"Cobalt Bromide (OUS)"(PDF). Archived fromthe original(PDF) on 2007-06-25. Retrieved2008-04-10.
Cobalt(I)
Cobalt(II)
Cobalt(0,III)
Cobalt(II,III)
Cobalt(III)
Cobalt(III,IV)
Cobalt(IV)
Cobalt(V)
Salts and covalent derivatives of thebromide ion
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