Thermodynamic stabilities of lanthanides-2-thiophenylhydrazodimedone complexes in dioxane-water media

The thermodynamic parameters for the formation of 1 : 1 and 1 : 2 complexes between lanthanide cations and 2-thiophenylhydrazodimedone (2-TPHD) have been determined by potentiometric titrations in 75% (v/v) dioxane-water solution of 0.1 M (KNO3) ionic strength. The stepwise Gibbs energies of metal complexes varied in the sequence, ΔG1 > ΔG2 and the stepwise enthalpies ΔH1 > ΔH2, and thus the stepwise entropies markedly increase in the order, ΔS1 >ΔS2. The non-linear variation of the thermodynamic parameters of the complex formation has been discussed in terms of differences in the donor ability of dioxane-water solvents. (author). 29 refs., 5 figs., 3 tabs