Competitive lithium-7 NMR study of the complexation of some alkaline earth and transition metal ions with 18-crown-6 in acetonitrile and its 50 : 50 mixtures with nitrobenzene and nitroethane

摘要

Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with 18-crown-6 (18C6) in pure acetonitrile and its 50:50 (w/w) mixtures with nitrobenzene and nitromethane. A competitive Li-7 NMR method was also employed to probe the complexation of Mg2+, Ca2+, Ba2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+ ions with 18C6 in the same solvent systems. In all solvents, the stability of the resulting 1:1 complexes was found to vary in the order Ba2+ > Ca2+ > Cd2+ > Mg2+ approximate to Cu2+ > Ni2+ > Co2+ > Zn2+. (C) 2000 Elsevier Science Ltd. All rights reserved. [References: 33]