NMR, IR, MS and elemental analysis, respectively. The X-ray single crystal analysis reveals that the macrocycle 3 has a folding structure, and 4 shows a twisted unfolding structure. The study for the reaction of the macrocyclic compound 3 or 4 with a series of the rare earth ions is performed by UV-Vis absorption spectra technique, and the results show that the macrocycle 3 displayed a selective recognition for La 3+ ion. Moreover, the JOB plot exhibited a 1∶1 (host∶guest) stoichiometry between the host 3 and La 3+ , and the binding constant (K) was determined using UV-vis titration method, K=7.59×10 3 .
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