Two novel 8-hydroxyquinoline connected dioxotetraamines have been designed and synthesized, and have been characterized by elemental analysis, IR, mass spectra and 1H NMR. The two ligands L1 and L2 have two chelating groups. Each can react with a transition metal ion forming complexes. Potentiometric titrations have been performed in 0.1 mol/L NaNO3 at 25_C giving the 1:1 stability constants. Coupled with UV spectroscopy the affinity of 8-hydroxyquinoline and dioxotetraamines to transition metal ions were compared and the possible structure of the metal complex species in solution was discussed. The results show that as to Mn2+, Zn2+ and Co2+, 8-hydroxyquinoline is a stronger chelating reagent than dioxo[13] or [14]tetraamine macrocycles and at 1:1 molar ratio (M:L), the former binds in 100% to the metal ions, while the dioxotetraamines can be only partially or not coordinated.
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