The electrochemical behavior and the absorption spectra, emission spectra, and luminescent lifetimes of the mixed-ligand complexes Rh(phpy),phen+, Rh(th~y)~phen+, Rh(~hpy)~biq+, and Rh(thpy)*biq+ (where phen is 1,lO-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(ph~y)~bpy+ and Rh(th~y)~bpy+ complexes (bpy = 2,2'-bipyridine), the [Rh(phpy),Cl], dimer, the homoleptic R h ( ~h e n ) ~~+ species, and the orthometalated Pt(phpy),-(CH2CI)C1 and Pt(thpy)2(CH2C1)C1 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 "-coordinating ligands.
Finally, the luminescence spectra show that the lowest energy excited state is predominantly ligand centered (on the NC-orthometalating ligands when N N = bpy or phen and on the NN-coordinating ligands when N N = 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.
specie^,'^ and the Pt(phpy),(CH2Cl)C1 and Pt-(thpy)2(CH2CI)C1 complexes.I5