Studies of the Intramolecular Aromatic-ring Stacking Interactions in the Ternary Platinum（Ⅱ） Complexes

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. 1mol/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.