| Abstract
| - Four compounds have been studied which contain ferrocene or octamethylferrocene donors linked by CH2 bridgesto cobaltocenium or pentamethylcobaltocenium acceptors. The electronic spectra of these compounds cannot beaccounted for by superposition of those of the constituent metallocenes; in each case, a low-energy solvatochromicabsorption is observed, the energy of which parallels the difference in electrode potentials between the iron andcobalt centers. This absorption is assigned to FeII-to-CoIII charge transfer; analysis using Hush theory givesdelocalization parameters V and α in the ranges 46−130 meV and 0.019−0.069, respectively, indicating muchstronger coupling between the metal centers than in structurally similar ferrocene/ferrocenium systems.
- Compounds in which ferrocene and cobaltocenium are linked by a methylene group show FeII-to-CoIII intervalence charge-transfer (IVCT) transitions in the visible, trends in the energies of which parallel electrochemical trends. Delocalization parameters are estimated to be in the ranges V = 46−130 meV and α = 0.019−0.069. These findings contrast with previous work on structurally similar ferrocenium/ferrocene mixed-valence species where no IVCT bands are found.
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