The Effective Electron‐Transfer Distance in Dinuclear Ruthenium Complexes Containing the Unsymmetrical Bridging Ligand 3,5‐Bis(2‐pyridyl)‐1,2,4‐triazolate

Electroabsorption (Stark effect) measurements on the intervalence charge‐transfer (IVCT) transitions in the diastereoisomers of [{Ru(bpy) 2 } 2 (μ‐bpt – )] 4+ [bpy = 2,2′‐bipyridine, bpt – = 3,5‐bis(2‐pyridyl)‐1,2,4‐triazolate] in n ‐butyronitrile glass at 77 K reveal effective charge‐transfer distances of 5.92 ± 0.03 Å for the ΔΛ/ΛΔ form and 5.44 ± 0.04 Å for the ΔΔ/ΛΛ form. These values correspond to approximately 95 and 88 %, respectively, of the geometrical metal–metal distance of 6.185(10) Å, obtained from the X‐ray crystal structure of the cation in the related complex (ΔΛ)‐[{Ru(Me 2 bpy) 2 } 2 (μ‐bpt – )](PF 6 ) 3 . The results are consistent with a localized Class II classification for the mixed‐valence systems [{Ru(pp) 2 } 2 (μ‐bpt – )] 4+ , where pp = bpy, Me 2 bpy = 4,4′‐dimethyl‐2,2′‐bipyridine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)