Cobalt(II) bromide

Cobalt(II) bromide

Structure of cobalt(II) bromide tetrahydrate
Crystal structure of cobalt(II) bromide
Anhydrous cobalt(II) bromide in a vial
Identifiers
CAS Number	7789-43-7  Y
3D model (JSmol)	Interactive image
ChemSpider	23012  Y
ECHA InfoCard	100.029.242
EC Number	232-166-7
PubChem CID	24610
RTECS number	GF9595000
UNII	7M7RX75BAL  Y
UN number	3077
CompTox Dashboard (EPA)	DTXSID50894158
InChI InChI=1S/2BrH.Co/h2*1H;/q;;+2/p-2 Y Key: BZRRQSJJPUGBAA-UHFFFAOYSA-L Y InChI=1/2BrH.Co/h2*1H;/q;;+2/p-2 Key: BZRRQSJJPUGBAA-NUQVWONBAJ
SMILES [Co](Br)Br
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) [1] [2] 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
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H312, H315, H317, H319, H332, H334, H335, H350
Precautionary statements	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)	2 0 1
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	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). Y  verify  (what is  YN ?) Infobox references

Cobalt(II) bromide refers to inorganic compounds with the formula CoBr₂·(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 as catalysts. ^[4]

Structure

The anhydrous compound has a cadmium iodide structure. The tetrahydrate is molecular, with the formula trans-[CoBr₂(H₂O)₄]. ^[5]

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: ^[3]

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

Anhydrous cobalt(II) bromide is hygroscopic. 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 by vacuum 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 with oxygen, forming cobalt(II,III) oxide and bromine vapor.^{[ citation needed ]}

The coordination compound bromopentaamminecobalt(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 a catalysts in organic synthesis. ^[8]

Safety

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

References

1. Cobalt Bromide Supplier & Tech Info American Elements
2. WebElements Periodic Table of the Elements
3. O. 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.
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 from the original (PDF) on 2007-06-25. Retrieved 2008-04-10.