Cation Binding Properties of Benzo-type Crown Ethers. Effect of Ring Size upon Complexation Phenomena

The cation-binding by a series of benzo-type crown ethers with different ring size has been performed by the solvent extraction of monovalent metal picrates (Na^+, K^+, Rb^+, Cs^+, Ag^+, and TI^+) between water and dichlolomethane. The effect of ring size and symmetry of the crown ethers upon the cation binding ability is discussed. The results are compared with those of commercially available crown ethers (dibenzo-18-crown-6 and 18-crown-6) and it was found that the less-symmetrical benzo-crown ethers have lower cation binding ability while unique cation selectivity for thallium (I) has been observed.