FACILITATED ION TRANSFER-REACTIONS ACROSS OIL WATER INTERFACES - PARTII - USE OF THE CONVOLUTED CURRENT FOR THE CALCULATION OF THE ASSOCIATION CONSTANTS AND FOR AN AMPEROMETRIC DETERMINATION OF THE STOICHIOMETRY OF MLJZ+ COMPLEXES/

Cyclic voltammetric experiments for reversible ion transfers across th e aqueous/organic interface facilitated by a neutral macrocyclic ligan d are presented for complexation reactions of 1:1 to 1:4 ion-to-ligand stoichiometries. The convoluted current is taken into account to deri ve general theoretical equations relating the half-wave potential to t he initial concentrations of both the metal Mz+ and the ligand L. Anal ytical relationships are obtained for both limiting cases of ligand an d, respectively, metal excess and for any type of reaction mechanisms. Likewise, considerations on the convoluted current provide a conditio n on the transition point between the diffusion regimes where either t he metal or the ligand limits the transfer, which constitutes an amper ometric determination of the complex stoichiometry. It is shown that t he half-wave potential depends on the various over-all association con stants, on the partition coefficient of the ligand and on the initial concentrations of both Mz+ and L. This dependence is the same for the TIC, TOC and TID mechanisms, but differs in the case of the ACT mechan ism. The theoretical predictions are corroborated by the results deduc ed from various calculated voltammograms and are verified experimental ly for the transfer of Pb2+ assisted by the thioether ligand 1,4,7,10- tetrathiacyclododecane at the water/1,2-DCE interface. Thanks to the s imulation, it is shown that the experimental current waves are due to 1:1 and 1:2 complex formation and that the first association constant in the organic phase is log K-1(0) approximate-to 5. (C) 1998 Elsevier Science S.A. All rights reserved.