Driving the Localized-to-Delocalized Transition in Unsymmetrical Dinuclear Ruthenium Mixed-Valence Complexes

Abstract

The degree of delocalization in the symmetrical complexes [{Ru(bpy)2}2(μ-dpb′)]5+ and [{Ru(bpy)2}2(μ-dpb)]5+ (dpb = 2,3-bis(2-pyridyl)-1,4-benzoquinoxaline; dpb′ = dipyrido(2,3-a;3′,2′-c)benzophenazine; bpy = 2,2′-bipyridine) is diminished by the substitution of the terminal bpy ligands at one end of the complex. The results of a classical analysis for the diastereoisomeric forms of the series of complexes [{Ru(bpy)2}(μ-BL){Ru(pp)2}]5+ (pp = bpy, Me2bpy (4,4′-dimethyl-2,2′-bipyridine), Me4bpy (4,4′,5,5′-tetramethyl-2,2′-bipyridine)) indicate that a greater degree of ground-state delocalization exists in the complexes incorporating the bridging ligand dpb′ compared with the dpb analogue. A two-state analysis in which ΔE 0 (the redox asymmetry) is varied at constant H ab (the electronic coupling) and λ (the reorganizational energy) does not adequately describe the properties of the systems due to the importance of a third electronic state corresponding to the bridging ligand.

Probing the Transition between the Localised (Class II) and Localised‐to‐Delocalised (Class II–III) Regimes by Using Intervalence Charge‐Transfer Solvatochromism in a Series of Mixed‐Valence Dinuclear Ruthenium Complexes

“…The energy differences between the IVCT bands for the diastereoisomers incorporating unfused bridging ligands may be regarded as redox asymmetry contributions to the electron transfer barrier in Equation (1), and denoted by DE struct . [15,16] While structural distortions are likely to be present in the series of complexes incorporating the unfused bridging ligands, and are observed in the solid-state structures of meso-[{RuA C H T U N G T R E N N U N G (bpy) 2 …”

“…These include solvent reorganisational contributions, [12] ion-pairing and temperature effects, [13] redox asymmetry contributions due to stereochemically induced structural distortions [14,15] and spin-orbit coupling contributions, [16] which are manifested by different electrochemical and IVCT properties for the diastereoisomeric forms of the same complex.…”