BINDING OF LITHIUM ION ISOTOPES WITH REDOX-ACTIVE MACROCYCLIC AND MACROBICYCLIC CROWN ETHERS

Three anthraquinone-containing crown ether macrocycles and one macrobicycle were reduced coulometrically to their corresponding anion radicals under vacuum. The resulting anion radical solutions in CH2Cl2 were stirred with an excess of a solid (LiClO4LiClO4)-Li-6-Li--7 mixture of known isotropic composition in order to form the appropriate Li+ complexes. After equilibration, the solution was separated from the excess solid and the (Li-6+]/[Li-7+] ratio was determined by atomic absorption spectrometry. The values were converted into the corresponding separation factors (alpha) after division by the original composition ratio of the solid mixture. The values were in the range 1.04-1.18. Except for one compound, 2, all of the reduced systems studied exhibited a much larger a value than the 1.057 reported for 12.crown-4 at 0-degrees-C in a liquid-liquid extraction system.