PROTONATION AND METAL COMPLEXATION STUDIES ON SOME OXA-DIAZA-MACROCYCLIC LIGANDS

Some 9- and 10-membered oxa-diaza macrocyclic ligands and their N-acetate derivatives have been synthesized and their protonation patterns studied by 1H NMR and potentiometric techniques. The stability constants of the complexes formed by these ligands with several alkaline-earth and first-series transition metal ions, zinc, cadmium and lead, were determined by potentiometry and the values were compared with those formed with the analogous 9-membered tri-aza macrocyclic ligands and with 12-membered oxa-triaza ligands. The substitution of one nitrogen by an oxygen atom in the backbone of the macrocyclic ring has pronounced effects both on the kinetics of the complexation reactions (faster equilibration) and on the stability of the metal complexes formed (decreased stability). The differences in this last case are analysed for two pairs of cyclic amines ([9]aneN3/[9]aneN2O and [12]aneN4/[12]aneN3O) with the first transition metal ions and for the corresponding N-acetate derivatives with the first transition and alkaline-earth metal ions. © 1990.