Complexation of alkali metal cations by calix[4]arene-bis-crown-6 in methanol, acetonitrile and propylene carbonate

The interactions of Li+, Na+, K+, Rb+, and Cs+ with the ''double-crown calix,'' calix[4]arene-bis-crown-6, have been studied in methanol, acetonitrile, and propylene carbonate at 25 degrees C using precise conductivity measurements. For Li+ and Na+ in solutions containing this calix[4]arene, only I:1 cation:ligand complexes are formed which permit the determination of the thermodynamic complexation formation constants, K-f. The conductivity data strongly suggest that 2:1 cation-calixarene complexes form with K+, Rb+, and Cs+. The existence of 2:1 complexes was experimentally confirmed for the potassium systems by a mass spectroscopic method.