THE SYNTHESIS AND CHARACTERIZATION OF MONOMERIC COMPLEXES OF RU(BPY)(2) WITH DIHYDROXYANTHRAQUINONES

The monomeric complexes, Ru(bpy)(2)1,4-DHAQ(+) and Ru(bpy)(2)1,5-DHAQ( +) (bpy=2,2'-bipyridine and DHAQ=dihydroxyanthraquinone), were synthes ized by the reaction of Ru(bpy)(2)Cl-2 . 2H(2)O with an excess of eith er 1,4-DHAQ or I,5-DHAQ. The complexes were purified chromatographical ly and characterized spectroscopically and electrochemically. Comparis ons between the data for these monomers and data from the correspondin g free ligands and ruthenium bipyridyl dimers were made. The lowest en ergy spectral transition in the visible region was assigned as an MLCT transition to the DHAQ based on the red shifting from monomer to the corresponding dimer and the solvatochromism of the transition. In aque ous solution the pK(a) for both the 1,4- and 1,5-DHAQ monomer was dete rmined to be 10.1+/-0.2 and for the 1,8-DHAQ monomer, 10.5+/-0.2. In a ll cases, pK(al) of the uncomplexed dihydroxyanthraquinones was more a cidic measured under the same conditions. From the properties of the c oordinated DHAQs attempts were made to evaluate whether they were sigm a donating or pi accepting.