ABSTRACT
Dynamic IR peak coalescence and simulations based on the optical Bloch equations have been used previously to predict the rates of intramolecular electron transfer in a group of bridged mixed valence dimers of the type [Ru3(O)(OAc)6(CO)L]-BL-[Ru3(O) (OAc)6(CO)L]. However, limitations of the Bloch equations for the analysis of dynamical coalescence in vibrational spectra have been described. We have used ultrafast 2D-IR spectroscopy to investigate the vibrational dynamics of the CO spectator ligands of several dimers in the group. These experiments reveal that no electron site exchange occurs on the time scale required to explain the observed peak coalescence. The high variability in FTIR peak shapes for these mixed valence systems is suggested to be the result of fluctuations in the charge distributions at each metal cluster within a single-well potential energy surface, rather than the previous model of two-site exchange.
ABSTRACT
Ruthenium clusters of the type [Ru3(µ3-O)(OAc)6(CO)(L)(nic)], where L = 4-dimethylaminopyridine (dmap) and nic = isonicotinic acid, form hydrogen-bonded mixed-valence dimers upon a single electron reduction. Electrochemical responses show two overlapping reduction waves, indicating the presence of a thermodynamically stable mixed-valence dimer with considerable electronic coupling across the hydrogen bond. Electronic spectra of the singly reduced hydrogen-bonded mixed-valence dimer reveal two intervalence charge transfer bands in the near-infrared region consistent with a Robin-Day class II system. These bands are assigned as metal-to-metal and metal-to-bridge charge transfer, and their behavior is best described by a semiclassical three state model. Infrared spectroscopy suggests localized behavior indicating electron transfer between the two clusters is slower than 10(10) s(-1).
