The Increasing Stability of Ternary Platinum(Ⅱ) Complexes by Intramolecular Aromatic-Ring Staking Interaction

The stability constants of the ternary mixed-ligand complexes of Pt(ArL)(NTP)n- (n=2 or 3) have been determined by potentiometric pH titration in aqueous solution (I=0.1 mol/L, KNO3; 25℃), where NTP refers to adenosine 5′-triphosphate (ATP) and uridine 5′-triphosphate (UTP); ArL refers to 1,10-phenanthroline (Phen), 2,2′-bipyridyl (Bpy), and L-tryptophane (Trp). The stability difference between the ternary complexes and the binary complexes has been compared and discussed. The increased stability in the ternary mixed-ligand complexes can be attributed to the cooperative effect of πA-πB and the intramolecular ligand-ligand aromatic-ring stacking interaction. The extent of the intramolecular aromatic-ring stacking interaction in the ternary platinum (Ⅱ) complexes has been calculated, which is in accord with the size of the aromatic rings forming the stack.