Abstract: The stability constants of some ternary mixed-ligand complexes, Pt(Phen)(CA)⁺, where Phen=1,10-phenanthroline and CA- =carboxylate, were determined by means of potentiometric pH titration in aqueous solutions(I=0.1 mol/L, KNO₃;25 ℃), and the stability of them was compared with that of the corresponding binary complexes.It was revealed that the ternary complexes containing phenylalkane carboxylates ligands(PCA^-) are much more stable than those formed with formate and acetate.The results indicate that there exist the intramolecular aromatic-ring interactions between the phenanthroline ring of Phen and the phenyl moiety of ligand PCA^- in the ternary mixed-ligand Pt(Phen)(PCA)^- complexes.The extent of the stacking interactions, which depends on the number of methylene groups between the phenyl moieties and the coordinated phenylalkane carboxylate groups, was calculated.The best-fitted stack was obtained for the complexes with 2-phenylacetate and 3-phenylpropionate as the ligands.

Key words: Platinum(Ⅱ), Mixed-ligand complex, Aromatic-ring stacking, Stability constant