Utilisation of Silver Cryptate [222] /Silver System as a Potential Reference for the Determination of the Solvation Transfer Coefficients of Ions. Stability of Cryptates in a Solvent Medium

Abstract

The formal potential of Ag 222] /Ag(s) system is supposed to be independent of the solvent, taking in account the 222] ligand structure and the corresponding cryptate. This extrathermodynamic hypothesis is confronted to the one usually considered, water, methanol, D. M. S. O., acetonitrile and tetramethylurea being the used solvents. It seems possible to generalize this hypothesis to other cations and cryptands. The stability constants of cryptate 222] of the evaluation of p^K _Ag222]⁺ constants, Nernst's law being respected. The argentometric titration of ligand 222] in presence of Na⁺, Li⁺, Tl⁺, Cd²⁺, Ni²⁺ ions allows to evaluate the p^K of corresponding cryptates in D. M. S. O. and methanol. Tl 222]⁺/Tl system follows Nernst's law in methanol and D. M. S. O. The dissociation constants have been evaluated from polarographic measurements in acetonitrile. The electrochemical systems are not rigorously fast, which does not allow an accurate determination of those constants by that method. Still it gives an order of magnitude.