), functioning as a hexadentate [[ligand]] -->
18-Crown-6 has a high affinity for the hydronium ion HO, as it can fit inside the crown ether.  Thus, reaction of 18-crown-6 with strong acids gives the cation . For example, interaction of 18-crown-6 with HCl gas in toluene with a little moisture gives an ionic liquid layer with the composition , from which the solid  can be isolated on standing.  Reaction of the ionic liquid layer with two molar equivalents of water gives the crystalline product .