Temperature coefficients of Ag/Ag+ and Ag/Ag+–cryptand 222 electrode potentials, thermodynamics of Ag+–cryptand 222 complex formation and molar transfer properties for Ag+ cations into aprotic media

Abstract

Temperature coefficients of the stability constants, d log K(Ag⁺222)/dT, of Ag⁺ complexes with cryptand 222, Ag⁺222 cryptate (Ag⁺222) have been derived from potentiometric titrations at different temperatures in acetone (Ac), acetonitrile (AN), propanenitrile (PN), butanenitrile (BuN), benzonitrile (BN), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidinone (NMP), dimethyl sulfoxide (DMSO), propylene carbonate (PC) and tetramethylene sulfone (sulfolane, TMS). The temperature coefficients of the standard electrode potentials, dE⁰/dT, for the Ag/Ag⁺ and Ag/Ag⁺222 couples have been derived from potentiometric measurements in a non-isothermal cell, where the reference electrode was kept at a constant temperature of 25 °C. It has been found that while the dE⁰/dT value for the Ag/Ag⁺ couple depends strongly upon the solvent, the corresponding temperature coefficient for the Ag/Ag⁺222 cryptate electrode is similar in all the solvents studied and can be approximated as dE⁰(Ag/Ag⁺222)/dT= 0.69 mV K^–1 with a standard error of 0.03 mV K^–1. Single-ion entropies of the Ag⁺ cation transfer from acetonitrile have been derived both from dE⁰(Ag/Ag⁺)/dT, applying the assumption of negligible thermal diffusion potential between cold and hot parts of the non-isothermal cell as well as from d log K(Ag⁺222)/dT, applying the ‘cryptate extrathermodynamic assumption’. Gibbs energies, enthalpies and entropies of silver(I) complexation by cryptand 222 agree well with literature data obtained employing different techniques.