Bromopentaamminecobalt(III) bromide is the dibromide salt of the cobalt
coordination compound
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...
with the formula
o(NH3)5Brsup>2+. It is a purple, water-soluble solid. The analogous
chloropentaamminecobalt(III) chloride is also well known.
Synthesis and reactions
The title compound is prepared by oxidation of a solution of cobalt(II) salts in aqueous ammonia.
:2 CoBr
2 + 8 NH
3 + 2 NH
4Br + H
2O
2 → 2
o(NH3)5Brr
2 + 2 H
2O
It was first reported in the 1870s, before the structure or even formulae were understood for such complexes. This early work showed that only two thirds of the bromide groups were exchangeable with other anions such as
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
and
dithionate
The dithionate (or metabisulfate) anion, , is a sulfur oxoanion derived from dithionic acid, H2S2O6. Its chemical formula is sometimes written in a semistructural format, as 3SSO3sup>2−. It is the first member of the polythionates.
The sul ...
.
The complex undergoes
aquation, meaning that bromide is displaced by water:
:
o(NH3)5Brr
2 + H
2O →
o(NH3)5(H2O)r
3
This process is catalyzed by platinum.
References
Further reading
*Loehlin, James H. "The Study of a Cobalt Complex-A Laboratory Project." Journal of Chemical Education.
*{{cite journal , title = Coordination complexes of cobalt: inorganic synthesis in the general chemistry laboratory , journal = Journal of Chemical Education , year = 1989 , author1 = Williams, Gregory M, author2 = Olmsted, John, III, author3 = Preksa, Andrew P., III , doi = 10.1021/ed066p1043, volume = 66 , issue = 12 , pages = 1043–5, bibcode = 1989JChEd..66.1043W
Bromides
Cobalt complexes
Cobalt(III) compounds
Ammine complexes
Bromo complexes