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-n]m (n = 2, 3; m = 2+ to 3-)

The mononuclear title complexes can exist as stereoisomers due to the unsymmetrically chelating α-azimino functionality of the abpy ligand. Both fac and mer isomers of [Ru(abpy) 3 ] 2+ and two out of the three possible diastcreoisomers of [Ru(abpy) 2 (bpy)] 2+ were isolated via HPLC and identified by virtue of their 1 H NMR spectra. Elcctrochemical potentials for several one-electron reduction steps and UV/vis spectroelectrochemical futures vary to a small but detectable degree for the respective pairs of isomers