Homochiral ion-pairing assisted by π-π stacking between Δ-[Ru(bpy)2(Hcmbpy)]2+ and Δ-Trisphat:: A quantitative investigation

The ion-pairing between the chiral Delta- or Lambda-[Ru(bpy)(2)(Hcmbpy)](2+) (Delta 1 or Lambda 1) and the Delta-Trisphat(-) (Delta 2) (Hcmbpy = 4-carboxy-4'-methyl-2,2-bipyridine and Trisphat = tris(tetrachlorobenzenediolato)phosphate(V)) is investigated in solution by means of H-1 NMR spectroscopy. The Ru-Trisphat ion-pairing adopts two stoichiometries that exchange via a fast dynamic process. The equilibrium constants K and K' are calculated for the 1/1 and 1/2 Ru/Trisphat stoichiometries. The constant values are in agreement with Coulombic attractions assisted by a pi-pi stacking between the bpy ligands of the Ru cation and the aromatic rings of the Trisphat anion. The homochiral pairing is favored as opposed to the heterochiral one, as shown by the respective K' values of 4.46 x 10(5) vs 2.05 x 10(5) M-2. In the homochiral ion pair, the cationic and anionic propellers adequately fit to optimize the pi-stacking interactions and to lead to a dication sandwiched by two anions at the highest Trisphat/Ru ratios.