Conductometric study of the complex formation of Rb+, Cs+, NH4 +, K+, Tl+ and Ag+ ions with several crown ethers in acetonitrile-dimethylsulfoxide and acetonitrile-dimethylformamide binary mixtures

Abstract

A conductance study of the interaction between Cs+, Rb+, NH4<br />+, K+, T1+ and Ag+ ions and<br />18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexyl-18-crown-6 (DC18C6),<br />dicyclohexyl-24-crown-8 (DC24C8), dibenzo-24-crown-8 (DB24C8) in different binary<br />mixtures of acetonitrile (AN) with dimethylsulfoxide (DMSO) and dimethylformamide (DMF)<br />at 25 °C has been carried out. Formation constants of the resulting 1:1 complexes were<br />determined from the conductance-mole ratio data and found frequently vary in the order<br />DC18C6 > 18C6 > B18C6 > DC24C8 > DB24C8 for Rb+ ion and DC18C6 > DC24C8 > 18C6<br />> B18C6 > DB24C8 for NH4<br />+ ion, DC24C8 > DC18C6 > 18C6 > B18C6 ≈ DB24C8 for Cs+<br />ion, DC18C6<br />> DC24C8 > 18C6 > B18C6 > DB24C8 for K+ ion, DC24C8 > DC18C6 > 18C6 > B18C6 ><br />DB24C8 for Tl+ ion and DC24C8 > DC18C6 > 18C6 > DB24C8 > B18C6 for Ag+ ion. It was<br />found that the stability of the resulting complexes increased by increasing acetonitrile mole<br />fraction in the solvent mixtures. The interactions of the solvent molecules with metal ions and<br />ligands show an important role for the complex formation process. Therefore, in addition to<br />influences of the solvent, the effects of the number of members in the macrocycle, nature of the<br />substituents in the polyether ring and cavity size are discussed.