Mixed-valence complexes solvent effects

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

One-electron oxidation of complexes [(bipy)2ClRu(II)LRu(II)Cl(bipy)2] where L is an unsaturated N-donor bridge yields mixed-valence complexes with FT bands.Effects of changing solvent polarity on the bands can be explained " using a dielectric continuum model which, with modification, can account for... 

Interestingly, an unusual mixed-valence state of a stacked tetrathiafulvalene (TTF) dimer was observed within the coordination host 1 at ambient temperature in an aqueous solution [10], When excess TTF was added to an aqueous solution of 1, the colorless solution became dark green in color because of the formation of a 1 D (TTF)2 complex (Fig. 4.3a). Electrochemical studies revealed that an initial one-electron oxidation occurred at -150 mV that led to the mixed-valence dimer, whereas a second one-electron oxidation at -300 mV afforded the cation radical dimer. The mixed-valence state was also indicated by the appearance of a broad absorption band in the near-infrared region ( max = -2000 nm) of the UV-vis spectrum (Fig. 4.3b). The host framework effectively forced the two molecules of TTF into close proximity in the cavity. As a result, the labile mixed-valence dimer was protected from oxygen and solvent molecules. 

---