SPECTROSCOPICAL AND ELECTROCHEMICAL-BEHAVIOR OF NEW MIXED-LIGAND CYCLOMETALATED RH(III) COMPLEXES

The absorption spectra, luminescence spectra, excited‐state lifetimes, and electrochemical behavior of the cyclometalated [Rh(ppz)2bpy]+, [Rh(3‐Cl‐ppz)2(bpy)]+, [Rh(4‐NO2‐ppz)2(bpy)]+, [Rh(ppz)2(biq)]+ and [Rh(4‐NO2‐ppz)2(biq)]+ complexes (ppz−, 3‐Cl‐ppz−, and 4‐NO2‐ppz− are the ortho‐C‐deprotonated forms of 1‐phenylpyrazole, l‐(3‐chlorophenyl)pyrazole and l‐(4‐nitrophenyl)pyrazole, respectively) have been investigated. The results obtained have been compared with those concerning the free protonated ligands and some previously studied mixed‐ligand cyclometalated Rh(III) complexes. Luminescence originates from the lowest ligand‐centered (LC) excited state, which involves the diimine ligands in all cases except for [Rh(4‐NO2‐ppz)2(bpy)]+, where it involves the ortho‐metalating ligand. s. In the absorption spectra, LC and metal‐to‐ligand charge‐transfer (MLCT) bands, involving the diimine and/or the ortho‐metalating ligands, have been assigned, and correlations between spectroscopic and electrochemical data are discussed. Copyright © 1990 Verlag GmbH & Co. KGaA, Weinheim