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.

Properties

When anhydrous, cobalt(II) bromide appears as green crystals. It is hygroscopic 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: Further heating to 130 °C produces the anhydrous form: The anhydrous form melts at 678 °C. 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].

Preparation and reactions

Cobalt(II) bromide can be prepared as a hydrate by the reaction of cobalt hydroxide with hydrobromic acid: The classical coordination compound bromopentaamminecobalt(III) bromide is prepared by oxidation of an aqueous solution of cobalt(II) bromide and ammonia. 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.