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.