Lanthanide complexes of 5-nitrophenol and its 1,3-Xylyl crown derivatives, 15-crown-4 and 18-crown-5, in aqueous solution

Abstract The stabilities of the one-one complexes of some lanthanide ions with p -nitrophenolate and its 1,3-xylyl crown derivatives, 15-crown-4 (I) and 18-crown-5 (II) , have been determined in aqueous solution at 25 °C by potentiometric measurements of the hydrogen ion concentration. Both the two cyclic ligands form complexes which are stronger than those of the p -nitrophenol, indicating that the ethereal chains are involved in the complex formation. A consideration of the stability constants as a function of the atomic number of the lanthanides obtained for the two cyclic ligands I and II suggests that in these coordination systems the phenoxide oxygen atom is the primary binding site while the ethereal oxygen atoms act as secondary binding sites with the metal ion probably located outside the cavity of the macroring.