In coordination chemistry, anation is the "replacement of the ligand water by an anion in a coordination entity."[1] The term is however used more loosely to include displacement of any neutral ligand by an anion.[2] The reaction is pervasive in coordination chemistry. The reverse reaction, displacement of an anionic ligand by water, is called aquation.


An example is the conversion of the aquo complex [Co(NH3)5(H2O)]3+ with bromide to give pentamminecobalt(III) bromide complex:

[Co(NH3)5(H2O)]3+ + Br → [Co(NH3)5Br]2+ + H2O

The mechanism of such reactions often invoke ion-pairing of the entering anion in the second coordination sphere followed by dissociation of the aquo ligand]].[2]


  1. IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006) "anation". doi:10.1351/goldbook.AT06766
  2. Ghosh, M. C.; Bhattacharya, P.; Banerjee, P., "Anation Reactions of Cobalt(Iii) Complexes", Coordination Chemistry Reviews 1988, 91, 1-34. doi:10.1016/0010-8545(88)80012-2
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.