LIGAND TO METAL CHARGE-TRANSFER TRANSITIONS IN RU(III) AND OS(III) COMPLEXES OF SUBSTITUTED 2,2'-BIPYRIDINES

The variations in the energy and intensity of the low-energy LMCT tran sitions have been examined in the complexes [M(X2-bpy)3]3+ and [M(bpy) n(X2-bpy)3-n]3+ (M = Ru or Os, X = Me, OMe, NH2 and NMe2). In the homo tris-chelates the energy of the low-energy LMCT transition falls with in a narrow range of 1.80 +/- 0.1 V for Ru(III) and 2.20 +/- 0.1 V for Os(III). The LMCT transition occurs at much lower energy in mixed lig and complexes. A quantitative analysis as a function of donor strength and Hammett substituent constants is presented.