RUI: CAS: Solvent-Free Synthesis of Transition Metal Halide Clusters

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With the support of the Chemical Synthesis program in the Division of Chemistry, Professor Dean Johnston of Otterbein University will develop new synthetic routes to substituted transition metal halide cluster materials that have potential future applications in bioimaging, liquid crystal and optical devices, catalysis, oxygen sensing, and as X-ray contrast agents. This family of clusters is strongly phosphorescent and has unique electrochemical properties, making the clusters potentially useful for a wide range of applications. The central cluster core is very stable, making it an ideal building block for the creation of new chemical constructs that link cluster units to form chains or three-dimensional networks. It is important to note that current solution-based methods for preparing modified clusters are severely limited by the reactivity and solubility of the products, restricting the types of materials that can be generated and isolated. This project seeks to overcome obstacles associated with current synthetic techniques. The research team will use thermal heating and mechanical grinding of metal cluster salts to prepare novel materials with potential applications for optical devices and sensing. Undergraduate students at Otterbein University will engage with this project through summer research experiences and activities integrated into the Inorganic Chemistry laboratory, gaining valuable experience in independent research and the synthesis and characterization of inorganic materials. These research experiences will complement the activities of the Cardinal Science Scholars Program, an NSF-supported program of academic, co-curricular, and non-academic activities demonstrated to increase retention and graduation in science, technology, engineering, and mathematics (STEM).This research project is directed toward the preparation of metal cluster synthons that are intended to serve as building blocks for new molecules and materials and to allow for precise control over connectivity and dimensionality of cluster materials. Greater than ninety-five percent of all known metal halide cluster derivatives are homoleptic, illustrating the difficulty in selective ligand substitution using solution-based synthetic routes. The Johnston research team will prepare metal halide cluster salts where the cation is selected to react with the anionic cluster, using charge balance and the properties of the cation to control the stoichiometry of the reaction. Reactions will be initiated by thermal or mechanochemical means in the absence of solvent, thereby avoiding complications from solvent interference or solubility issues. The reactions and products will be analyzed using thermogravimetric analysis, in-situ Raman spectroscopy, and powder and single-crystal X-ray diffraction methods. The results of this research are expected to provide researchers in the field of inorganic cluster chemistry with synthetic tools and pathways to prepare new cluster-based materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.