A double origin proposed for the various Mössbauer spectra of biferrocenium salts: charge ordering and molecular bistability Original Research Article

We propose a general explanation for the various Mössbauer spectra of biferrocenium salts, based on the ambiguous character of the HOMO (highest occupied molecular orbital) of the moieties of these mixed-valence salts. This way we both reproduce fusion-type and coexistence-type spectra. Orbital crossovers involved by the model are recognized as an effect of molecular bistability.