Oxonium Ions from Aqua Regia:  Isolation by Hydrogen Bonding to Crown Ethers

The preparation and structures of a variety of oxonium ion tetrachloroaurate(III) salts isolated from aqua regia are reported. The new compounds are [(H5O2)2(12-crown-4)2][AuCl4]2 (1), [(H7O3)(15-crown-5)][AuCl4] (2), [(H5O2)(benzo-15-crown-5)2][AuCl4] (3), [(H3O)(18-crown-6)][AuCl4] (4), [(H5O2)(dibenzo-24-crown-8)][AuCl4] (5), [(H5O2)(4-nitrobenzo-15-crown-5)2][AuCl4] (6), [(H3O)(4-nitrobenzo-18-crown-6)][AuCl4] (7), [(H11O5)(tetrachlorodibenzo-18-crown-6)2][AuCl4] (8), and [(H7O3)(dinitrodibenzo-30-crown-10)][AuCl4] (9). A significant correlation between the degree of proton hydration and crown ether size is observed. Aryl crown ethers are nitrated in concentrated aqua regia, but nonnitrated products may be obtained in a dilute solution of aqua regia by reaction with aqueous HAuCl4.