ION-PAIRING IN THE ANALYSIS OF VOLTAMMETRIC DATA AT THE ITIES - RBTPBAND RBTPBCL IN 1,2-DICHLOROETHANE

The association of rubidium-tetraphenylborate (RbTPB) and rubidium-tet rakis(-chlorophenyl)borate (RbTPBCl) ion pairs in the organic solvent 1,2-dichloroethane (DCE) have been obtained from condutivity and volta mmetric data. Conductivity measurements given K-RbTPBCl = 43 100 M(-1) and yield a lower bound for K-RbTPB (K-RbTPB > 70 000 M(-1). The latt er association constant is at variance with the previously accepted va lue. A method for analysing voltammetric data which allows for the det ermination of the association constants is presented. The positive pol arization limit where the transfer of Rb+ takes place is shifted by ca . 200 mV when changing the anion of the organic base electrolyte from TPB- to TPBCl-. If we interpret this shift in terms of the association constant, then K-RbTPB = 7.4 . 10(7) M(-1). The values of K-RbTPB and K-RbTPCl are discussed in terms of the classical theories by Bjerrum and Fuoss. Finally, we consider if the preferential solvation of p-chl orophenyl rings of TPBI- could account for the observed difference bet ween the values of the association constants.