NEW POTASSIUM-SELECTIVE AND CESIUM-SELECTIVE IONOPHORIC BIS(CROWN ETHER)S DERIVED FROM XANTHENE-4,5-DICARBOXYLIC ACID

A series of bis(crown ether)s based-upon a xanthene-4,5-dicarboxylic a cid skeleton was prepared and their ionophoric properties toward alkal i metal cations were investigated. Bis(crown ether)s bearing 15-crown- 5 and 18-crown-6 moieties exhibited pronounced extraction efficiencies toward K+ and Cs+ ions, respectively, and the extraction constant est imated by solvent extraction studies was as high as 10(9) for the 2-K and 3-Cs+ systems. Using UV titration of potassium picrate with 2 in THF, the complex was found to have a structure of a completely encapsu lated guest in the host. In transport experiments, the bis(crown ether )s showed no significant selectivity pattern compared with extraction results, again implying the strong complexation of bis(crown ether)s. Ion-selective electrode studies also demonstrated that the selective i onophoric properties of 2 toward K+ were reminiscent of the natural an tibiotic valinomycin except for a somewhat slow response.