[7Li] NMR measurements were used to determine the stoichiometry and stability of Li+ complexes with 18-crown-6 and dicyclohexyl-18-crown-6 in nitromethane and acetonitrile solutions. A competitive [7Li] NMR technique was also employed to probe the complexation of Ba2+, Pb2+, Cd2+, and UO22+ ions with the same crown ethers–solvent systems. All the resulting 1 : 1 complexes were more stable in nitromethane than acetonitrile solution. In all cases, the stability of both crown complexes in nitromethane and acetonitrile varied in the order Pb2+ > Ba2+ > Li+ > Cd2+ > UO22+.