A POTENTIOMETRIC AND CALORIMETRIC STUDY OF THE THERMODYNAMICS OF FORMATION OF SOME OF THE COMPLEXES OF THE d10METAL IONS SILVER(I), MERCURY(II), AND CADMIUM(II) WITH THIODIGLYCOL, THIOUREA, AND THE SULPHITE ION

Abstract

Abstract The standard free energy, enthalpy, and entropy changes of complex formation of the d 10 metal ions Ag(I), Hg(H), and Cd(II) with the S-donor-atom ligands thiodiglycol, thiourea, and sulphite were investigated at 298.15 ± 0.05 K. The free-energy changes δGi ° were calculated from stability constants βi, which were determined by silver- and mercury-electrode potentiometry, if suitable literature data were not available. Enthalpy changes δHi°, were measured with a titration calorimeter, and entropy changes δSi ° were calculated from the relation δGi °=δHi ° TδSi °. The standard state, denoted by the superscript ° in δG δH, and TδS°, refers, in most cases, to a hypothetical 1 M solution in which the ionic strength, μ, is 0.5 M. It is demonstrated that a large proportion of the extra stabilization of the HgL n complexes compared with the corresponding AgLn complexes is a result of a more favourable entropy contribution. The entropies of complexation are interpreted in terms of the Powell, Latimer, an...