Cobalt(II) bromide
Chemical compound
From Wikipedia, the free encyclopedia
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]
4.svg) Structure of cobalt(II) bromide tetrahydrate | |
-bromide-xtal-packing-3D-bs-17.png) Crystal structure of cobalt(II) bromide | |
_bromide.jpg) Anhydrous cobalt(II) bromide in a vial | |
| Identifiers | |
|---|---|
3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.029.242 |
| EC Number |
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PubChem CID |
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| RTECS number |
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| UNII | |
| UN number | 3077 |
CompTox Dashboard (EPA) |
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| 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)[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) | |
| 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: | |
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| 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 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).
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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.