Lithium-7 NMR study of the exchange kinetics of the lithium ion with cryptand C221 in methanol solution. Temperature dependence of the exchange mechanism

摘要: Abstract The exchange kinetics of Li+C221 cryptate in methanol solution was studied by lithium-7 NMR line-shape analysis at a wide range temperature. Depending on the temperature, two different mechanisms were found to coexist extents. A dissociative pathway dominates high temperatures (from 5 25°), while bimolecular mechanism prevails lower −30 −60°C). At temperature 5°C, both and contribute metal exchange. For pathway, activation parameters calculated as: Ea=22±2 kJ mol−1; ΔH‡ =20±2 ΔS‡=−144±8 J mol−1 K−1. While for they are: Ea=9.9±0.4 ΔH‡=8.0±0.4 ΔS‡ =−146±2