| Abstract
| - A homogeneous series of mixed-valence compounds [R-Fc(4-py)Ru(NH3)5]3+ were synthesized and characterized. Their IT bands are solvent and substituent dependent and found to vary almost exclusively with the energetic difference between the donor and acceptor sites. An empirical equation incorporating Gutmann solvent donor numbers (DN) and Hammett substituent constants (σ), Eop = 0.82 + 0.019 (DN) + 0.44σ eV, was found to finely tune Eop of this series within 94% accuracy.
- A homogeneous series of heterobimetallic complexes of [R-Fc(4-py)Ru(NH3)5](PF6)2 (R = H, Et, Br, acetyl;Fc(4-py) = 4-ferrocenylpyridine) have been prepared and characterized. The mixed-valence species generated insitu using ferrocenium hexafluorophosphate as the oxidant show class II behavior, and the oxidized sites areruthenium centered. ΔE1/2, E1/2(FeIII/FeII) − E1/2(RuIII/RuII), an upper limit for ΔG° that is an energetic differencebetween the donor and acceptor sites, changes sharply and linearly with Gutmann solvent donor number (DN)and Hammett substituent constants (σ). The solvent-dependent and substituent-dependent intervalence transferbands were found to vary almost exclusively with ΔE1/2. The activation energy for the optical electron transferversus ΔE1/2 plot yields a common nuclear reorganization energy (λ) of 0.74 ± 0.04 eV for this series. Theequation that allows one to incorporate the effect of both solvent donicity and substituents on optical electrontransfer is Eop = λ + ΔG°, where ΔG° = (ΔG°)intrinsic + (ΔG°)solventdonicity + (ΔG°)substituenteffect. (ΔG°)intrinsicwith a numerical value of 0.083 ± 0.045 eV was obtained from the intercept of the ΔE1/2 of [H-Fc(4-py)Ru(NH3)5]2+,3+,4+ versus DN plot. (ΔG°)solventdonicity was obtained from the average slopes of the ΔE1/2 of [R-Fc(4-py)Ru(NH3)5]2+,3+,4+ versus DN plot, and (ΔG°)substituenteffect was obtained from the average slopes of thecorresponding ΔE1/2 versus σ plot. The empirical equation allows one to finely tune Eop of this series to Eop =0.82 + 0.019(DN) + 0.44σ eV at 298 K, and the discrepancy between the calculated and experimental data isless than 6%.
|
