Charge and Spin Delocalization in Mixed-Valent Vinylruthenium–Triarylamine-Conjugates with Planarized Triarylamines

We report on three new vinylruthenium–triarylamine (TA) conjugates with planarized TA substituents. The neutral, mono-, and dioxidized forms of the complexes were scrutinized by UV/vis/NIR, IR, and EPR spectroscopies as well as by quantum chemical calculations. By analyzing the intervalence charge-transfer (IVCT) transitions of the mixed-valent radical cations, we obtain information on the extent of electronic coupling between the chemically different redox sites. Completely delocalized Ru-MeTA+ shows a vibrationally structured, non-solvatochromic IVCT band. Decreased blueshifts of the indicative Ru(CO) stretching vibration during the first oxidation and larger A(14N) EPR hyperfine splitting constants in concert with smaller g-values indicate enhanced TA contributions to the singly occupied molecular orbital of the other two complexes Ru-TOTA•+ and Ru-DOTA•+ and hence less symmetrical charge and spin density distributions. This is also reflected by the solvatochromism and the asymmetric shape of the IVCT band with a smaller bandwidth at the low-energy side. Temperature-dependent UV/vis/NIR spectroscopy of mixed-valent Ru-TOTA•+ and Ru-DOTA•+ revealed that the band skewing is due to the vibrational coupling of the IVCT transition to symmetrical vibrations, placing these radical cations near or at the class II/III borderline according to Robin and Day.