REDUCTIVE QUENCHING OF NOVEL MIXED-LIGAND TRIS(BIPYRIDYL)RUTHENIUM(II) COMPLEXES IN AQUEOUS-SOLUTION AND INERT COLLOIDAL SUSPENSIONS

The reductive quenching of the lowest energy electronically excited st ate of four mixed-ligand tris(bipyridyl)ruthenium(II) complexes by ani onic ascorbate and N-phenylglycine electron donors was investigated in aqueous solution at pH greater than or equal to 5.0. The central ruth enium(II) metal atom is coordinated to either two 2,2'-bipyridine (bpy ) or two 4,4'-dicarboxy-2,2'-bipyridine (dcbpy) ligands to render the complexes a net 2+ ([Ru(bpy)(2)(L)](2+)) or 2- ([Ru(dcbpy)(2)(L)](2-)) charge. Reductive quenching was found to proceed with a larger bimole cular rate constant (k(q) = 1.2-7.4 x 10(8) M(-1) s(-1)) than that pre viously measured for the quenching of the parent Ru(bpy)(3)(2+) by asc orbate. Moderate yields (phi(ce), = 0.20-0.40) of the reduced metal co mplex were formed in the process. The reductive quenching of the diani onic complexes in homogeneous solution was compared with that in suspe nsions (pH 5.0) of inert colloidal alumina-coated silica particles, wh ere both:the anionic donor and the chromophore are coadsorbed to the c ationic particles. The apparent bimolecular rate constants were found to be enhanced by more than 1 order of magnitude in these colloidal sy stems, with a concomitant decrease in the yield of redox products esca ping from the solvent cage.