NMR-STUDY OF THE LIGAND INTERCHANGE OF HEXACYCLEN AND HEXAMETHYLHEXACYCLEN COMPLEXES WITH TL-PERCENT METHANOL SOLUTION( ION IN 70)

The exchange kinetics of Tl+ complexes with hexacyclen and hexamethylh exacyclen were studied in 70% methanol solution by proton NMR line-sha pe analysis. In Tl+-hexacyclen system, a dissociative mechanism is fou nd to be predominant at higher temperatures, while a bimolecular pathw ay may become more important at lower temperatures. In contrast, the T l+-hexamethylhexacyclen system solely prefers a dissociative exchange mechanism in entire temperature range studied. The corresponding excha nge rates and the activation parameters E-a, Delta H-double dagger, De lta S-double dagger and Delta G(double dagger) for the exchange have b een determined, and the possible parameters controlling the exchange r ates and mechanisms are discussed.