THERMODYNAMICS OF COMPLEX-FORMATION OF AG(I) .9. INVESTIGATIONS OF AG(I) THIOUREA THIOACETAMIDE HALIDE-SYSTEMS IN AQUEOUS-SOLUTION

Mononuclear complex formation in the systems Ag(I)-thiourea-thioacetam ide-halide (Cl-, Br-, I-) has been investigated in aqueous solution at constant ionic strength, mu = 1 for KNO3, and different temperatures. Predominance diagrams for two-ligand Ag(I)-thiourea-thioacetamide-hal ide and three-ligand Ag(I)-thiourea-thioacetamide-halide systems are s hown at 25-degrees-C. The suitability of the exponential model Y = A B exp(-CX) for describing free energy relationships between the subst ratum-to-ligand mutual chemical affinities Y and the overall thermodyn amic stabilities X of the reacting substrata is stressed. Compensative enthalpy-entropy relationships have been found both in the overall an d the stepwise complex formation. It is confirmed that favourable enth alpy and unfavourable entropy changes do not necessarily follow soft-s oft interactions in aqueous solution. In the formation of monocoordina te AgL, thiourea and thioacetamide are enthalpically and entropically sharply discriminated in spite of the ligands having the same donor at om.