2,2'-Azobis(pyridine) (abpy) as a multiply reducible tetradentate ligand. EPR evidence for the configurational dependence of intramolecular electron transfer in the stereoisomeric tris-chelate ruthenium complexes Ru(abpy)n(bpy)3-nm (n = 2, 3; m = 2+ to 3-). Inorganic Chemistry, (32)15:3362--3368, 1993. [PUMA: azabispyridine bipyridine electrochem isomer isomer;electronic redn ruthenium spectra]