Cobalt(II) bromide

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.

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) 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

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.^{[citation needed]}

Safety

Exposure to large amounts of cobalt(II) can cause cobalt poisoning.^[6] Bromide is also mildly toxic.