PROPERTIES AND KINETICS OF DIHYDROXYANTHRAQUINONE AND DIAMINOANTHRAQUINONE RUTHENIUM BIPYRIDYL DIMERS

Ru(bpy)(2)Cl-2 (bpy: 2,2'-bipyridine) reacts with 1,4-diaminoanthraqui none (1,4-DAAQ) to produce a dimeric complex which precipitates from s olution in its mixed-valence form. Redox couples show that the rutheni ums are easier to oxidize than those in the corresponding 1,4-DHAQ (1, 4-dihydroxyanthraquinone) and 1,4-AHAQ (1-amino-4-hydroxyanthraquinone ) dimers and give a value of 2.8 x 10(6) for K-com. Visible absorption bands are broad and may be combinations of transitions. The IT band i n acetonitrile shows structure with lambda(max) (log epsilon) at 845 n m (3.5), 1493 nm (4.11) and 2028 nm (4.04). Preliminary kinetic studie s of the S2O82- oxidation of the 1,4-DHAQ, 1,4-AHAQ and 1,4-DAAQ dimer s show a faster oxidation of the fully reduced form ([2,2]) followed b y a slower oxidation of the mixed-valence form ([2,3]). No mechanism c ould be determined for the faster oxidation. However, the slower oxida tion appeared to be first order in both dimer and S2O82-, and involved ion pairing. K-ip was determined to be 13 for the 3+,2 -ion pair. Val ues for k(et) were found to parallel the second ruthenium oxidation po tential for the dimers, and were found to be 6x10(-4), 8x10(-4) and 1. 1x10(-2) M-1 s(-1) for the 1,4-DHAQ, 1,4-AHAQ and I,4-DAAQ dimers, res pectively, at 25 degrees C. (C) 1998 Elsevier Science S.A.