GROUND-STATE INTERACTIONS BETWEEN RUTHENIUM(II)-DIIMINE COMPLEXES ANDPHENOL AND MONOCHLOROPHENOLS IN AQUEOUS-SOLUTION

Ground-state interactions between Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridin e) or Ru(bpz)(3)(2+) (bpz = 2,2'-bipyrazine) and phenol (PhOH) or mono chlorophenols (ClPhOH) have been investigated in aqueous (D2O) solutio n by NMR. The upfield shifts of the resonances and the NOE difference spectra of the complexes in the presence of the phenols indicate the p resence of offset face-to-face pi-stacking interactions between the ph enol and the aromatic ligands. Electron withdrawal from the phenol rin g by the monochloro substituent and less effective solvation by aqueou s (compared to acetonitrile) media favor the interaction. The formatio n constant for the 1:1 Ru(bpy)(3)(2+)-PhOH complex is estimated to be similar to 0.01 M-1; K is smaller for Ru(bpz)(3)(2+) than for Ru(bpy)( 3)(2+), and it increases for both complexes in the order PhOH < 4-ClPh OH < 3-CIPhOH < 2-CIPhOH.