Intervalence transfer in biferricenium and biferricenylenium cations

Iron-57 Mössbauer spectra were obtained (300 and 4.2°K) for the singly oxidized ``mixed-valence'' molecules, biferricenium triiodide and biferricenylenium triiodide. The first compound showed two quadrupole-split doublets (Δ Eq≃ 2.0 and 0.4 mm/sec) while the last system only exhibited one quadrupole-split doublet (ΔEq = 1.7 mm/sec). Intervalence-transfer electronic absorption was detected for the biferricenium system at 5100 cm−1 and for the biferricenylenium system at 6790 cm−1. A discussion of the thermal rate of intervalence transfer in these systems is given.