Lithium-7 NMR Study of the Exchange Kinetics of the Lithium Ion With Crypt and C221 in Nitromethane and Dimethylformamide Solutions

Abstract

The exchange kinetics of Li + C221 cryptate in nitromethane (NM) and dimethylformamide (DMF) solutions was studied by lithium-7 NMR line-shape analysis at a wide range of temperature. Depending on the nature of solvent, two different exchange mechanisms were found to exist. At entire temperature range studied, a bimolecular mechanism dominates in NM, while a dissociative pathway prevails in DMF solution. In NM solution, the activation parameters were calculated as: E a = 9.3 ± 0.3 kJ mol" 1 ; ΔΗ* = 8.9 ± 0.4 kJ mol" 1 ; AS* = -150 ± 1 J mol" 1 K" f . While, in DMF solution, they are: E a = 9.2 ± 0.1 kJ mol" 1 ; ΔΗ* = 8.9 ± 0.4 kJ mol" 1 ; AS* = -169 ± 1J mol" 1 K" 1 .