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 (H(5)O(2))(2)(12-crown-4)(2)]AuCl(4)](2) (1), (H(7)O(3))(15-crown-5)]AuCl(4)] (2), (H(5)O(2))(benzo-15-crown-5)(2)]AuCl(4)] (3), (H(3)O)(18-crown-6)]AuCl(4)] (4), (H(5)O(2))(dibenzo-24-crown-8)]AuCl(4)] (5), (H(5)O(2))(4-nitrobenzo-15-crown-5)(2)]AuCl(4)] (6), (H(3)O)(4-nitrobenzo-18-crown-6)]AuCl(4)] (7), (H(11)O(5))(tetrachlorodibenzo-18-crown-6)(2)]AuCl(4)] (8), and (H(7)O(3))(dinitrodibenzo-30-crown-10)]AuCl(4)] (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 HAuCl(4).