Infrared study of the Class II/Class III boundary in mixed-valence dinuclear ruthenium complexes

The cyanamide stretching frequencies of the mixed-valence complexes [{Ru(NH 3)(5)}(2)(mu -L)](3+), trans,trans-[{Ru(NH3)(4)(py)}(2)(mu -L)](3+) (py = p yridine), and mer,mer-[{Ru(NH3)(3)(bpy)}(2)(mu -L)](3+) (bpy = 2,2'-bipyrid ine), where L is the 1,4-dicyanamidobenzene dianion and its substituted der ivatives in nitromethane, acetonitrile, and dimethyl sulfoxide, were examin ed to determine the effects of inner- and outer-sphere perturbation on elec tron delocalization. The solvent-dependent infrared spectra of [{Ru(NH3)(5) }(2)(mu -Me(2)dicyd)](3+), where Me(2)dicyd(2-) is the 2,5-dimethyl-1,4-dic yanamidobenzene dianion, yield evidence for a transformation from localized to delocalized behavior; and confirm the effect of outer-sphere perturbati on on the mixed-valence state. The IR spectrum of trans,trans-[{Ru(NH3)(4)( py)}(2)(mu -Me(2)dicyd)](3+) in acetonitrile is consistent with Class III p roperties, and this complex's properties can be regarded as benchmarks for delocalization in our systems. It is shown that this complex obeys the gene ral condition for delocalization in symmetric mixed-valence complexes, 2H = lambda, and possesses an experimental free energy of resonance exchange De ltaG'(r) = 1250 cm(-1) and resonance exchange integral H = 3740 cm(-1).