Mössbauer and ESR Spectroscopic Studies on the Mixed-Valence States of 1′,1'″-Dialkyl- and 1′,1'″-Bis(methylbenzyl)biferrocenium Triiodides in Crystalline and Dispersed State

Abstract
Iron atoms in the two different crystal forms of 1′,1'″-dibutylbiferrocenium triiodide showed different temperature-depending mixed-valence states; i.e., an averaged-valence state at higher temperatures and a trapped-valence state at lower temperatures in one crystal form but only a trapped-valence state from 78 K to room temperature in the other crystal form. The temperature-depending mixed-valence states were observed in 1′,1'″-diisobutylbiferrocenium triiodide, whereas only a trapped-valence state was found in 1′,1'″-dipentylbiferrocenium triiodide. Both the 1′,1'″-dibutyl- and 1′,1'″-diisobutylbiferrocenium triiodide showed Mössbauer spectra that were different from those of their crystalline states in a dispersed state. A good correlation of the anisotropy of g-values with the mixed-valence states was observed in the ESR spectra for a series of 1′,1'″-dialkyl- and 1′,1'″-bis(methylbenzyl)biferrocenium triiodides. The difference in the ESR parameters between these compounds in the crystalline state was reduced in the dispersed state.

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