Variable Noninnocence of Substituted Azobis(phenylcyanamido)diruthenium Complexes
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The synthetic chemistry of substituted 4,4′-azobis(phenylcyanamide) ligands was investigated, and the complexes [{Ru(tpy)(bpy)}2(μ-L)][PF6]2, where L = 2,2′:5,5′-tetramethyl-4,4′-azobis(phenylcyanamido) (Me4adpc2–), 2,2′-dimethyl-4,4′-azobis(phenylcyanamido) (Me2adpc2–), unsubstituted (adpc2–), 3,3′-dichloro-4,4′-azobis(phenylcyanamido) (Cl2adpc2–), and 2,2′:5,5′-tetrachloro-4,4′-azobis(phenylcyanamido) (Cl4adpc2–), were prepared and characterized by cyclic voltammetry and vis–near-IR (NIR) and IR spectroelectrochemistry. The room temperature electron paramagnetic resonance spectrum of [{Ru(tpy)(bpy)}2(μ-Me4adpc)]3+ showed an organic radical signal and is consistent with an oxidation-state description [RuII, Me4adpc•–, RuII]3+, while that of [{Ru(tpy)(bpy)}2(μ-Cl2adpc)]3+ at 10 K showed a low-symmetry RuIII signal, which is consistent with the description [RuIII, Cl2adpc2–, RuII]3+. IR spectroelectrochemistry data suggest that [{Ru(tpy)(bpy)}2(μ-adpc)]3+ is delocalized and [{Ru(tpy)(bpy)}2(μ-Cl2adpc)]3+ and [{Ru(tpy)(bpy)}2(μ-Cl4adpc)]3+ are valence-trapped mixed-valence systems. A NIR absorption band that is unique to all [{Ru(tpy)(bpy)}2(μ-L)]3+ complexes is observed; however, its energy and intensity vary depending on the nature of the bridging ligand and, hence, the complexes’ oxidation-state description.
