Czech-German Cooperation Project: Structure studies on inner and outer functionalized icosahedral and bicapped square-antiprismatic boron clusters

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This is an application for a joint Czech/German collaboration project. The Czech part has been submitted to Czech Science Foundation by Dr. Drahomir Hnyk, Institute of Inorganic Chemistry of the Academy of Science of the Czech Republic. The project aims at the structure determination of functionalized carbaborane-cluster molecules, namely functionalized dicarba-closo-decaboranes (1,2-C2B8H10) and 1,2-dicarba-closo-dodecaborane (1,2-C2B10H12) with some of the terminal hydrogen atoms substituted by EH units (where E = S, Se, Te). These compounds will be used by the Prague group as architecturally rigid building blocks as parts of self assembled monolayer (SAM) based materials. The knowledge of structural data of the underlying molecules is of importance for the application of these compounds in this area. The determination of molecular structures of such boron-cluster molecules by the standard method of structural chemistry, X-ray diffraction (XRD), is often difficult due to limited crystallization ability of the compounds. Therefore we want to apply gas electron diffraction (GED) for this purpose and study the unperturbed structure of the molecules in the gaseous state. The Bielefeld group is one of a few centers worldwide running equipment for GED. Besides pure structure determination, these compounds are ideal candidates for further development of new strategies in GED data analysis. This will also be part of this project. These developments aim at higher precision, reliability and reproducibility of the structural data. This new refinement strategy, introduced by Dr. Vishnevskiy in our group, uses regularization during least-squares refinements by a full set of calculated restraints and allows adjusting the weight of theoretical input into analysis of experimental data. For the first time we want to combine this approach with structural information gained by other methods like microwave spectroscopy. It will also be tried to apply specialized forms of crystallization (in-situ crystallization) to obtain suitable specimen for XRD experiments. In combination with gas-phase data of free molecules this will give information on the molecular structure distortions by changing the phase. These will also allow studying the charge density distribution of the functionalized carborane clusters, and consequently gaining insight into further molecular properties relevant for their use in SAM-based material chemistry.