INFLUENCE OF THE PIEPHO-MODE ON CHARGE ORDERING IN MIXED-VALENCE BIFERROCENIUM SALTS - MOSSBAUER-SPECTRA

A model of phase transitions in biferrocenium salts is proposed. For t he first time for dimeric clusters, the role of the a-bridge-b stretch ing mode (Piepho-mode) in the charge-ordered phase stabilization is ex amined. Depending of the sign of the interaction parameter this mode i s shown to contribute to 'extra' electron localization or delocalizati on. First and second order phase transitions are elucidated to be poss ible, Within the framework of the proposed model different types of Mo ssbauer spectra resembling the experimental situation are obtained. (C ) 1998 Elsevier Science B.V.