Bromopentaamminecobalt(III) bromide

Bromopentaamminecobalt(III) bromide

Identifiers
CAS Number	14283-12-6
Properties
Chemical formula	[Co(NH3)5Br]Br2
Molar mass	383.798 g/mol
Appearance	Purple
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Bromopentaamminecobalt(III) bromide is a cobalt coordination compound with the formula [Co(NH₃)₅Br]Br₂. It is a purple, water-soluble solid.

Synthesis and reactions

The title compound is prepared by oxidation of a solution of cobalt(II) salts in aqueous ammonia.^[1]

2 CoBr₂ + 8 NH₃ + 2 NH₄Br + H₂O₂ → 2 [Co(NH₃)₅Br]Br₂ + 2 H₂O

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 and dithionate.^[2]

The complex undergoes aquation, meaning that bromide is displaced by water:

[Co(NH₃)₅Br]Br₂ + H₂O → [Co(NH₃)₅(H₂O)]Br₃

This process is catalyzed by platinum.^[3]

References

1. Diehl, Harvey; Clark, Helen; Willard, H. H. (1939). "Bromopentamminocobalti Bromide". Inorganic Syntheses. 1: 186. doi:10.1002/9780470132326.ch66.
2. Jörgensen, S. M. (1879). "Beiträge zur Chemie der Kobaltammoniakverbindungen. II. Ueber die Bromopurpureokobaltsalze". Journal für Praktische Chemie. 19: 49. doi:10.1002/prac.18790190110.
3. Archer, M. D.; Spiro, M. (1970). "Heterogeneous Catalysis in Solution. Part VIII. Catalysis of the Aquation of the Bromopentaamminecobalt(III) Ion by Metallic Platinum". Journal of the Chemical Society (1): 78–81.

Further reading

• Loehlin, James H. "The Study of a Cobalt Complex-A Laboratory Project." Journal of Chemical Education. ACS Publications, Dec. 1982. Web.
• Williams, Gregory M.; Olmsted, John; Brekda, Andrew P, December 1989.“Coordination Complexes of Cobalt.” Journal of Chemical Education 66 number 12.