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Cobalt(II) bromide

326.74 g/mol (hexahydrate) Red-purple crystals (hexahydrate) 2.46 g/cm3 (hexahydrate) 66.7 g/100 mL (59 °C) 68.1 g/100 mL (97 °C) hexahydrate: 113.2 g/100 mL (20 °C) 58.6 g/100 mL (methanol, 30 °C) soluble in methyl acetate, ether, alcohol, acetone 47 °C (hexahydrate) | NFPA-H = 2 | NFPA-F = 0 | NFPA-R = 1 | NFPA-S = cobalt(II) chloride cobalt(II) iodide nickel(II) bromide

Cobalt(II) bromide refers to inorganic compounds with the formula . The anhydrous form (n = 0) is a green solid and the hexahydrate (n = 6) is a red solid. These compounds find some use as catalysts.{{cite journal |title=Multicomponent Synthesis of Tertiary Diarylmethylamines: 1-((4-Fluorophenyl)(4-methoxyphenyl)methyl)piperidine |journal=Organic Syntheses |date=2012 |volume=89 |page=283 |doi=10.15227/orgsyn.089.0283|first1=Erwan |last1=Le Gall|first2=Thierry|last2=Martens

Structure

The anhydrous compound has a cadmium iodide structure. The tetrahydrate is molecular, with the formula trans-[CoBr2(H2O)4].

Preparation and reactions

Cobalt(II) bromide form by treating an aqueous suspension of cobalt(II) carbonate with hydrobromic acid according to the following idealized equation: :

Anhydrous cobalt(II) bromide is hygroscopic. Air exposure eventually forms the hexahydrate in air, 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: : The resulting solid can be purified by vacuum sublimation at 500 °C.

Further heating to 130 °C produces the anhydrous form: :CoBr2·2H2O → CoBr2 + 2 H2O

At higher temperatures, cobalt(II) bromide reacts with oxygen, forming cobalt(II,III) oxide and bromine vapor.

The coordination compound bromopentaamminecobalt(III) bromide is prepared by oxidation of an aqueous solution of cobalt(II) bromide and ammonia. :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. Bromide is also mildly toxic.

References

References

  1. [http://www.americanelements.com/cobr.html Cobalt Bromide Supplier & Tech Info] [[American Elements]]
  2. [http://www.webelements.com/webelements/compounds/text/Co/Br2Co1-7789437.html WebElements Periodic Table of the Elements]
  3. (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.
  4. (1963). "Handbook of Preparative Inorganic Chemistry, 2nd Ed.". Academic Press.
  5. Perry, Dale L.. (2011). "Handbook of Inorganic Compounds". Taylor & Francis.
  6. (1939). "Inorganic Syntheses".
  7. (1973). "Diamantane: Pentacyclo[7.3.1.14,12.02,7.06,11]Tetradecane". Organic Syntheses.
  8. "Cobalt Bromide (OUS)".
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cobalt(ii)-compounds bromides metal-halides
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