Double salts with a multifunctional character made from Zintl phases and oxo- as well as halogeno-metalates

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This research project aims for the development of fundamental compounds for new functional materials by means of synthetic solid-state chemistry through the combination of two inorganic components at the molecular ionic level. The focus is on deltahedral, polyanionic germanium and tin clusters comprising nine atoms, that are in combination with a second type of anion such as oxometalates and metal-halide anions form new, hybrid semiconducting solid state materials (double salts). Due to their mutual structural tunability, the combination of both alkali-metal Zintl phases and alkali-metal metal-oxides or metal-halides offers numerous possibilities for the generation and design of new multi-component hybrid materials. Since double salts can appear with variable composition, this compound class has the potential for tunable band gaps. The new material class has application potential in optoelectronics and, in principle, also as a water splitting catalyst.In a first step, synthesis protocols for double salts are systematically developed based on the few known representatives and are applied to various other combinations. The new compounds are structurally characterized by means of X-ray diffraction methods and Raman spectroscopy. Basic electronic properties such as band gaps or magnetic properties, oxidation states of the constituting elements that suggest a possible charge transfer between the units, are determined experimentally. Using quantum chemical calculations, on the one hand, the electronic structures and band gaps are calculated. On the other hand, stable, new, unknown candidates with hybrid character are identified on the basis of structural relationships and tested with regard to thermodynamic stability using theoretical methods. In a further step, selected candidates are specifically synthesized using the synthesis protocols developed. Specifically, in the project applied for here, hybrid compounds are produced which contain the polyanions [Ge9]4–, [Sn9]4– and [M@Sn9] x– as component 1 and metal-oxide or metal-halide anions of the [MO4]x– (M = transition metal) or tetrahedrally coordinated halides (e.g. [SnBr4]2–, [PbBr4]2–, [MX4]x-; X = halogen) or halides of the type [MX6]x- (M = Sn, Pb) as component 2. The structural units of both components are known as alkali-metal compounds, however in combination they are systematically developed here for the first time. Component 2 is already used today in metallic bronzes and in solar cells. The combination enables charge-transfer processes between the building units of the components and better tunable band gaps.