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 Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...

in some processes.

Properties

When

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

, cobalt(II) bromide appears as green crystals. It is

hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...

and 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 Further heating to 130 °C produces the anhydrous form: :CoBr₂·2H₂O → CoBr₂ + 2 H₂O The anhydrous form melts at 678 °C. At higher temperatures, cobalt(II) bromide reacts with

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

, forming

cobalt(II,III) oxide Cobalt is a chemical element; it has symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, ...

and

bromine Bromine is a chemical element; it has chemical symbol, symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between th ...

vapor. The tetrahydrate is molecular, with the formula ''trans''- oBr₂(H₂O)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 A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

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 o(NH₃)₅Brr₂ + 2 H₂O Triphenylphosphine complexes of cobalt(II) bromide have been used as a

s in organic synthesis.

Safety

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

References

{{bromides Cobalt(II) compounds Bromides Metal halides