Thermodynamics of substituted rhodanine IV: Potentiometric studies of 3-(p-tolylsulphonamido)rhodanine transition metal complexes.

Proton-ligand dissociation and metal-ligand stability constants of 3-(p-Tol ylsulphonamido)rhodanine (TSR) with some transition metal ions were calcula ted potentiometrically in 0.1 M KCl and 20%(v/v) ethanol-water mixture. The order of stability constants was found to be: Th4+ > UO22+ > Gd3+ > Ce3+ > La3+ > Mn2+ < Co2+ < Ni2+ < CU2+ > Zn2+ The dissociation constants pK(H) o f TSR and the stability constants log K of their complexes were determined at different temperatures (303, 308 and 318 K). The corresponding thermodyn amic parameters (Delta G, Delta H and Delta S) were derived and discussed. The dissociation process is non-spontaneous. endothermic and entropically u nfavourable. The formation of the metal complexes have been Found to be spo ntaneous, exothermic or endothermic (depend on the metal) and entropically favourable. The stoichiometries of these complexes were determined spectrop hotometrically and indicated the formation of 1:1 and 1:2 (metal:lignad) co mplexes.