Conductance study of ion-pairing of alkali tetraphenylborate and picrate complexes with some substituted macrocyclic polyethers in acetonitrile

Abstract

The conductance of sodium and potassium tetraphenylborate and picrate complexes with bis(4-tert-butylbenzo)-18-crown-6 (mtbDBC) in acetonitrile solutions at 25°C was analysed according to the Fuoss-Hsia equation. Values of the limiting conductances, Λ 0, and ion-pair dissociation constants, K D , are reported. Tetraphenylborate complexes are more dissociated than the corresponding picrate complexes, as are also mtbDBC complexes compared to those of dtbDBC. A large ion-pair association of dtbDBC complexes can be attributed not only on less cation complex stability, but also to the lack of solvation of these large complex ions. The results obtained are compared with those obtained for the conductance of sodium and potassium tetraphenylborates and picrates in acetonitrile, with the data relative to the complexes of polyether dibenzo-18-crown-6, and are discussed in terms of the polyether interactions with alkali cation which are controlled by their size, solvent interactions with alkali cation and polyether complexed cation, size and charge density of the anion, and the steric hindrance effects caused by the butyl substituents in the polyether molecule.