Gooden, Velton M.; Dasgupta, Tara P.; Gordon, Nancy R.; Sadler, Garfield G.
Author Affiliation, Ana.
Department of Chemistry
Properties and kinetics of dihydroxy- and diaminoanthraquinone ruthenium bipyridyl dimers
Inorganica Chimica Acta
Date of Publication
Ru (bpy)2Cl2 (bpy: 2,2' -bipyridine) reacts with 1,4-diaminoanthraquinone (1,4-DAAQ) to produce a dimeric complex which precipitates from solution in its mixed-valence form. Redox couples show that the rutheniums 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 2.8x106 for kcom. Visible absorption bands are broad and may be combinations of transitions. The IT band in acetonitrile shows structure with lmax (log e ) at 845 nm (3.5), 1493 nm (4.11) and 2028 nm (4.04). Preliminary kinetic studies of the S2O8² - oxidation of the 1,4-DHAQ, 1,4-AHAQ and 1,4-DAAQ dimers show a fatser oxidation of the fully reduced form ([2,2]) followed by a slower oxidation of the mixed-valence form ([2,3]). No mechanism could be determined for the faster oxidation. However, the slower oxidation appeared to be first order in both dimer and S2O8² -, and involved ion pairing. Kip was determined to be 13 for the 3+,2- ion pair. Values for ket were found to parallel the second ruthenium oxidation potential 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 1,4-DAAQ dimers, respectively at 25º C.....