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

a conductance study of the interaction between cs+, rb+, nh4+, k+, t1+ and ag+ ions and18-crown-6 (18c6), benzo-18-crown-6 (b18c6), dicyclohexyl-18-crown-6 (dc18c6),dicyclohexyl-24-crown-8 (dc24c8), dibenzo-24-crown-8 (db24c8) in different binarymixtures of acetonitrile (an) with dimethylsulfoxide (dmso) and dimethylformamide (dmf)at 25 °c has been carried out. formation constants of the resulting 1:1 complexes weredetermined from the conductance-mole ratio data and found frequently vary in the orderdc18c6 > 18c6 > b18c6 > dc24c8 > db24c8 for rb+ ion and dc18c6 > dc24c8 > 18c6> b18c6 > db24c8 for nh4+ ion, dc24c8 > dc18c6 > 18c6 > b18c6 ≈ db24c8 for cs+ion, dc18c6> dc24c8 > 18c6 > b18c6 > db24c8 for k+ ion, dc24c8 > dc18c6 > 18c6 > b18c6 >db24c8 for tl+ ion and dc24c8 > dc18c6 > 18c6 > db24c8 > b18c6 for ag+ ion. it wasfound that the stability of the resulting complexes increased by increasing acetonitrile molefraction in the solvent mixtures. the interactions of the solvent molecules with metal ions andligands show an important role for the complex formation process. therefore, in addition toinfluences of the solvent, the effects of the number of members in the macrocycle, nature of thesubstituents in the polyether ring and cavity size are discussed.