Mixed-Valence States of 1,1"-Bis(2-phenylbutyl)-1,1"-biferrocenium(1+) Triiodides: Effects of the Cation Symmetry and Counter Anion on the Electron-Transfer Rate

The effects of cation symmetry and packing on the mixed-valence state of binuclear ferrocene derivatives are discussed by using chiral isomers and the racemic modification of 1ʹ,1ʹ"-bis(2-phenylbutyl)-1,1"-biferrocenium(1+) triiodide. Although the three chiral isomers showed trapped-valence states at 78 K, only the (R,S) isomer showed a perfect detrapped-valence state at room temperature in the three isomers. The racemic modification consisted of the (R,R) and the (S,S) isomers showed a perfect detrapped-valence state at room temperature. This shows that the packing effect overcomes the effect of cation asymmetry. The electron-transfer rate for each pentaiodide salt was faster than that of the corresponding triiodide salt. A comparison between the (S,S) triiodide and the (S,S) pentaiodide salts reveals an important packing effect. The polymeric pentaiodide skeleton forced the (S,S) cation to have pseudo-inversion center.