Aquation

Aquation is the chemical reaction involving "incorporation of one or more integral molecules of water" with or without displacement of other atoms or groups.^[1] The term is typically employed to refer to reactions of metal complexes where an anion is displaced by water. For example, bromopentaamminecobalt(III) undergoes the following aquation reaction to give a metal aquo complex:^[2]

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

This aquation reaction is catalyzed both by acid and by base. Acid catalysis involves protonation of the bromide, converting it to a better leaving group. Base hydrolysis proceeds by the S_N1cB mechanism, which begins with deprotonation of an ammonia ligand.