SYNTHESIS AND PROPERTIES OF 5-CHLORO-8-HYDROXYQUINOLINE-SUBSTITUTED AZACROWN ETHERS - A NEW FAMILY OF HIGHLY METAL ION-SELECTIVE LARIAT ETHERS

New 5-chloro-8-hydroxyquinoline (CHQ)-substituted aza-18-crown-6 (4), diaza-18-crown-6 (1), diaza-21-crown-7 (2), and diaza-24-crown-8 (3) l igands, where CHQ was attached through the 7-position, and aza-18-crow n-6 (11) and diaza-18-crown-6 (10) macrocycles, where CHQ was attached through the 2-position, were prepared. Thermodynamic quantities for c omplexation of these CHQ-substituted macrocycles with alkali, alkaline earth, and transition metal ions were determined in absolute methanol at 25.0 degrees C by calorimetric titration. Two isomers, 1 and 10, w hich are different only in the attachment positions of the CHQ to the parent macroring, exhibit remarkable differences in their affinities t oward the metal ions. Compound 1 forms very stable complexes with Mg2, Ca2+, Cu2+, and Ni2+ (log K = 6.82, 5.31, 10.1, and 11.4, respective ly), but not with the alkali metal ions. Ligand 10 displays strong com plexation with K+ and Ba2+ (log K = 6.61 and 12.2, respectively) but n ot with Mg2+ or Cu2+. The new macrocycles and their complexes have bee n characterized by means of UV-visible and H-1 NMR spectra and X-ray c rystallography. New peaks in the UV spectrum of the Mg2+-1 complex cou ld allow an analytical determination of Mg2+ in very dilute solutions in the presence of other alkali and alkaline earth metal cations. H-1 NMR spectral and X-ray crystallographic studies indicate that ligand 1 0 forms a cryptate-like structure when coordinated with K+ and Ba2+, w hich induces an efficient overlap of the two hydroxyquinoline rings. S uch overlapping forms a pseudo second macroring that results in a sign ificant increase in both complex stability and cation selectivity.