Abstract：The synthesis of macrocyclic ligands appended with fluorescent or chromogenic chelators is a promising approach to developing metal-ion chemosensors because of the ion selectivity of macrocyclic ligands and the fluorescence or chromogenic response of the appended chelating groups. In the present paper, 1,10-dioxa-4,7,13,16-tetraaza-18-crown-6(L1) and 4,7,13,16-tetra(2-hydroxy-5-nitrobenzyl)-1,10-dioxa-4,7,13,16-tetraaza-18-crown-6(L2) were synthesized and characterized via elemental analysis and 1H NMR spectrum. The complexation properties of L2 for H+, Ce3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+ and Yb3+ were studies by UV-Vis method in H2O-DMSO (φ=1/4) mixed solvent, and the stability constants of the complexes were determined. The results obtained indicate that the absorption peak of azacrown ether L2 at 314 nm was shifted toward long wavelength with increasing pH from 1.85 in the investigated solution. A new absorption peak appeared at 400 nm while increasing pH to 7.4, and the wavelength of peak position and absorption intensity were increased gradually with increasing pH. When rare earth ions were added to the solution, the absorption peak of L2 above 400 nm was shifted toward short wavelength, and absorption intensity was increased obviously in comparison with L2 alone. Thus the formation of the complex was verified, and it was formed at pH＞7.0. The stability constants of the complexes obtained show that stability of the complexes depends upon the match between cavity dimension of L2 and size of the rare earth ions. There was a decrease in stability of complex with decreasing the radius of rare earth ion in the order of Ce3+＞Nd3+＞Sm3+＞Eu3+＞Gd3+＞Tb3+＞Dy3+＞Yb3+.
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