Charge delocalization of 1,4-benzenedicyclometalated ruthenium: A comparison between tris-bidentate and bis-tridentate complexes

A dimetallic biscyclometalated ruthenium complex, [(bpy) ₂Ru(dpb)Ru(bpy) ₂] ²⁺ (bpy = 2,2′- bipyridine; dpb = 1,4-di-2-pyridylbenzene), with a tris-bidentate coordination mode has been prepared. The electronic properties of this complex were studied by electrochemical and spectroscopic analysis and DFT/TDDFT calculations on both rac and meso isomers. Complex [(bpy) ₂Ru(dpb)Ru(bpy) ₂] ²⁺ has a similar 1,4-benzenedicyclometalated ruthenium (Ru-phenyl-Ru) structural component with a previously reported bis-tridentate complex, [(tpy)Ru(tpb)Ru(tpy)] ²⁺ (tpy = 2,2′;6′,2″- terpyridine; tpb = 1,2,4,5-tetra-2-pyridylbenzene). The charge delocalizations of these complexes across the Ru-phenyl-Ru array were investigated and compared by studying the corresponding one-electron-oxidized species, generated by chemical oxidation or electrochemical electrolysis, with DFT/TDDFT calculations and spectroscopic and EPR analysis. These studies indicate that both [(bpy) ₂Ru(dpb)Ru(bpy) ₂] ³⁺ and [(tpy)Ru(tpb)Ru(tpy)] ³⁺ are fully delocalized systems. However, the coordination mode of the metal component plays an important role in influencing their electronic properties.