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) ligands, where CHQ was attached through the 7-position, and aza-18-crown-6 (11) and diaza-18-crown-6 (10) macrocycles, where CHQ was attached through the 2-position, were prepared. Thermodynamic quantities for complexation 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, which are different only in the attachment positions of the CHQ to the parent macroring, exhibit remarkable differences in their affinities toward the metal ions. Compound 1 forms very stable complexes with Mg(2+), Ca(2+), Cu(2+), and Ni(2+) (log K = 6.82, 5.31, 10.1, and 11.4, respectively), but not with the alkali metal ions. Ligand 10 displays strong complexation with K(+) and Ba(2+) (log K = 6.61 and 12.2, respectively) but not with Mg(2+) or Cu(2+). The new macrocycles and their complexes have been characterized by means of UV-visible and (1)H NMR spectra and X-ray crystallography. New peaks in the UV spectrum of the Mg(2+)-1 complex could allow an analytical determination of Mg(2+) in very dilute solutions in the presence of other alkali and alkaline earth metal cations. (1)H NMR spectral and X-ray crystallographic studies indicate that ligand 10 forms a cryptate-like structure when coordinated with K(+) and Ba(2+), which induces an efficient overlap of the two hydroxyquinoline rings. Such overlapping forms a pseudo second macroring that results in a significant increase in both complex stability and cation selectivity.

A new macrocyclic compound capable of forming a pseudo second macroring upon complexation has been characterized. The compound, 5 -chloro-8-hydroxy quinoline (CHQ)-substituted diaza-18-crown-6 (1), exhibits unique complexing properties, log K values for the formation of K+ and Ba2+ complexes with 1 in methanol are larger than those for the K+ and Ba2+ complexes with all other lariat ethers. The log K value for the 1-Ba2+ complex is the same magnitude as that of the cryptand [2.2.2]-Ba2+ complex. Selectivity factors for Ba2+ over other alkalineearth cations and for K+ over Na+ in methanol are > 10* 1234567 and ~103, respectively, which are the highest factors ever reported for lariat ethers. Moreover, the selectivity of 1 for Ba2+ over other alkaline-earth cations is larger than that of any other cryptand studied to date. UV-visible, NMR spectral, and X-ray crystallographic studies indicate that a pseudo second macroring is formed through -interaction between the two CHQ rings upon complexation with K+ and Ba2+. This effect results in a cryptate-like structure and therefore highly stable complexes with high selectivity for these cations. 2H20 (Spectrum), SrBr2 (Spectrum), and BaBr2 (Johnson Matthey).

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