Ionic solvation. Part 6.—Standard potential of Ag/Ag+cryptand (222, 221 and 211) electrode in aprotic media

Abstract

It has been shown that the cryptate and the liquid junction potential (NLJP) assumptions used together lead to the conclusion that the standard potential of the M/M⁺L electrode (M⁺ is the metal cation and L is the cryptand molecule) is similar in different aprotic solvents, according to the formula E°(M/M⁺L, solvent 1)=E°(M/M⁺L, solvent 2)+A, where A is a function of the cryptate and cryptand transfer energies, ΔG°_t, and of the liquid junction potential, E_LJ between solvents: A=[ΔG^°_t(L, S₁→ S₂)–ΔG^°_t(M⁺L, S₁→ S₂)]/F–E_LJ.

The Ag⁺222, Ag⁺221 and Ag⁺211 systems have been examined in ten aprotic solvents. It has been found that, in general, the combination of the NLJP and cryptate assumptions is not valid (A≠ 0). It may happen that A= 0, as is the case for the Ag⁺222, DMSO → PC system, but in some cases A is as large as 60–77 mV.

The stability constants of the silver(I) cryptates and free energies of transfer of the silver(I) cation between the solvents have been obtained. The Ag/Ag⁺ cryptand electrode has been proposed as a reference one.