INTRAMOLECULAR RELAXATION DYNAMICS AND INFRARED-SPECTRA OF DIAZA MACROCYCLIC COMPLEXES WITH NA+ AND AG+ IN PROPYLENE CARBONATE

Ultrasonic relaxation spectra and infrared spectra (N-H stretch) are reported for the macrocycles 1,10-diaza-18-crown-6 (Kryptofix 22), monoaza-18-crown-6, and 18-crown-6 (18C6) and their complexes with Na+ and Ag+ in the solvent propylene carbonate (PC) at 25-degrees-C. The relaxation spectra are attributed to intramolecular conversions on the microsecond to nanosecond time scale between various conformers of the macrocyclic ligands. When Na+ is present, a shift of the relaxation frequencies for Kryptofix 22 and the appearance of a new relaxation process at f < 1 MHz with monoaza-18C6 are recorded. Infrared spectra suggest the existence of more than one configuration of the ligand, this being evident both with and without Na+ in PC. For Ag+ complexes of diaza-18C6 in PC, the formation constant is too high for the two observed relaxation processes to be consistent with a previously envisaged three species mechanism involving the complete rotation of the nitrogens, one of them carrying Ag+. Rather the three species are visualized as conformers of the same endo-endo species. The IR spectra seem to confirm this view.