Influence of the Piepho-mode on charge ordering in mixed-valence biferrocenium salts: Mössbauer spectra Original Research Article

A model of phase transitions in biferrocenium salts is proposed. For the first time for dimeric clusters, the role of the a-bridge-b stretching mode (Piepho-mode) in the charge-ordered phase stabilization is examined. Depending of the sign of the interaction parameter this mode is shown to contribute to `extraʹ electron localization or delocalization. First and second order phase transitions are elucidated to be possible. Within the framework of the proposed model different types of Mössbauer spectra resembling the experimental situation are obtained.