The electrochemical behavior and the absorption spectra, emission spectra, and luminescent lifetimes of the mixed-ligand complexes Rh(phpy)2phen+, Rh(thpy)2phen+, Rh(phpy)2biq+, and Rh(thpy)2biq+ (where phen is 1,10-phenanthroline, biq is 2,2'-biquinoline, and phpy" and thpy" are the ortho-C-deprotonated forms of 2-phenylpyridine and 2-(2-thienyl)pyridine) have been studied. The results obtained have been compared with those previously available for the analogous Rh(phpy)2bpy+ and Rh(thpy)2bpy+ complexes (bpy = 2,2'-bipyridine), the [Rh(phpy)2Cl]2 dimer, the homoleptic Rh(phen)33+ species, and the orthometalated Pt(phpy)2-(CH2C1)C1 and Pt(thpy)2(CH2Cl)Cl complexes. The results obtained indicate that, as reported previously by Ohsawa et al., the NN-coordinating ligands are easier to reduce than the NC-orthometalating ligands. The absorption spectra, however, show that the lowest energy MLCT band involves the NC-orthometalating ligands rather than the easier to reduce NN-coordinating ligands.Finally, the luminescence spectra show that the lowest energy excited state is predominantly ligand centered (on the NC-orthometalating ligands when NN = bpy or phen and on the NN-coordinating ligands when NN = biq) in nature. These results show that in these complexes there are several closely spaced levels of different orbital nature and confirm that a localized description of their electronic structure can only be an approximation.
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