A NEW HIGHLY SELECTIVE MACROCYCLE FOR K- EFFECT OF FORMATION OF A PSEUDO 2ND MACRORING THROUGH COMPLEXATION( AND BA2+ )

A new macrocyclic compound capable of forming a pseudo second macrorin g upon complexation has been characterized. The compound, 5-chloro-8-h ydroxyquinoline (CHQ)-substituted diaza-18-crown-6 (1), exhibits uniqu e complexing properties. log K values for the formation of K+ and Ba2 complexes with 1 in methanol are larger than those for tie K+ and Ba2 + complexes with all other lariat ethers. The log K value for the 1-Ba 2+ complex is the same magnitude as that of the cryptand [2.2.2]-Ba2complex. Selectivity factors for Ba2+ over other alkalineearth cations and for K+ over Na+ in methanol are > 10(7) and similar to 10(3), res pectively, which are the highest factors ever reported for lariat ethe rs. 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, H-1 NMR spectral, and X-ray crystallographic studies indicate that a pseudo second macroring is formed through pi-pi interaction be tween the two CHQ rings upon complexation with K+ and Ba2+. This effec t results in a cryptate-like structure and therefore highly stable com plexes with high selectivity for these cations.