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 (${\mathrm{\Delta \; E}}_q\text{≃ 2.0}$ and 0.4 mm/sec) while the last system only exhibited one quadrupole‐split doublet (ΔE_q = 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.