Mixed-valence state of symmetric diruthenium complexes: synthesis, characterization, and electron transfer investigation.

Complexes of the type {[(pyS)Ru(NH(3))(4)](2)-μ-L}(n), where pyS = 4-mercaptopyridine, L = 4,4'-dithiodipyridine (pySSpy), pyrazine (pz) and 1,4-dicyanobenzene (DCB), and n = +4 and +5 for fully reduced and mixed-valence complexes, respectively, were synthesized and characterized. Electrochemical data showed that there is electron communication between the metal centers with comproportionation constants of 33.2, 1.30 × 10(8) and 5.56 × 10(5) for L = pySSpy, pz and DCB, respectively. It was also observed that the electronic coupling between the metal centers is affected by the π-back-bonding interaction toward the pyS ligand. Raman spectroscopy showed a dependence of the intensity of the vibrational modes on the exciting radiations giving support to the assignments of the electronic transitions. The degree of electron communication between the metal centers through the bridging ligands suggests that these systems can be molecular wire materials.