Electronic Structural Studies of the Ru3(III,II,II) Mixed-Valent State of Oxo-Centered Triruthenium Clusters

The anionic state of basic ruthenium acetate complexes of the type [Ru3O­(OAc)6]­(CO)­(L1)­(L2) (L = 4-cyanopyridine, pyridine, and N,N-dimethylaminopyridine) feature pronounced optical transitions in the near-infrared region indicative of strongly coupled mixed-valence states. A series of these clusters was prepared and studied spectroscopically in tandem with density functional theory (DFT) computational results to construct an orbital structure–function description of how the electron density is shared between the ruthenium centers in this mixed-valent state. The mixed-valency manifests itself as a combination of the nonbonding atomic orbitals of the equivalent ruthenium centers, with increased energetic splitting between the orbitals with symmetries appropriate for more efficient electronic communication. This DFT-based model agrees with the Marcus–Hush description of mixed-valency, with the added knowledge that specific orbitals contribute to different degrees in the electronic coupling between two redox centers.