Gemischtvalente Bimetallocen-Verbindungen: spektroskopische Eigenschaften und intermolekulare Wechselwirkungen
This work is concerned with mixed valence bimetallocenes along with the analysis of characteristic interactions connected with the phenomenon of mixed valence. Singly and doubly bridged homo- and heteronuclear bimetallocenes are synthesized and analyzed to determine their electronic, vibronic and elastic interactions. Mößbauer as well as optical spectroscopy are used as a powerful tool to probe these interactions. Density functional theoretical calculations support the interpretation of these optical properties and the analysis of relevant vibrational data. Using Mößbauer spectroscopy the temperature dependent charge localization-delocalization process of mixed valence biferrocenium compounds is monitored. This process can be influenced due to elastic interactions by doping crystals with analogous heterobimetallic ferrocenyl-cobaltocenium dimers which do not show temperature dependent charge distribution behaviour. Electronic absorption spectra of the singly and doubly bridged ferrocenyl-cobaltocenium and ferrocenylene-cobaltocenylenium salts are presented and fully assigned. Low energy IVCT-like (IVCT= Intervalent Charge Transfer) metal-metal charge transfer transitions give information according to the electronic interaction of the subunits. Interestingly a stronger electronic interaction was found for the singly bridged compound which could be explained in terms of the respective electronic and geometric structures. Optical spectra of solutions and crystallites of the homobimetallic compounds biferrocenium-triiodide and 1´-1´´´-diethylbeferrocenium-triiodide reveal the presence of a known low-energy transition in the NIR range but also an additional transition in the MIR range that has not been reported yet. These absorptions are assigned to different IVCT transitions based on the molecular orbital scheme. In order to analyze these absorptions a four-state Vibronic Coupling Configuration Interaction (VCCI) model based on the well known PKS model is developed and applied to simulate these spectra, giving electronic and vibronic coupling parameters. A temperature dependent asymmetry is used to describe the temperature dependence of the solid state spectra. This asymmetry influences the temperature dependent charge delocalization process of mixed valence biferrocenium salts.