High-pressure investigations on binary and ternary acetylides

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This project focuses on high-pressure investigations of binary and ternary acetylides. A recently approved large-volume press (LVP), which is expected to be available at the University of Cologne at the end of 2021, will be used for this purpose. The aim of the project is to synthesise so-called polycarbides, which have already been predicted for almost 10 years on the basis of theoretical work, in mg quantities and to carry out a detailed structural characterisation. Since interesting properties, e.g. superconductivity, are predicted for these polycarbides, these compounds shall also be characterised beyond pure structural analysis (e.g. conductivity measurements). In investigations described so far, diamond anvil cells have been used almost exclusively, which only allow (partly limited) in-situ characterisation. In addition, heating was not used in most experiments, which is why no crystalline products could be obtained due to presumably kinetic inhibitions. These limitations should be overcome with the above-mentioned LVP, as both heating to temperatures above 1500 °C is possible (at 15 GPa) and mg quantities of the products can be obtained to enable further investigations. All investigations so far indicate that the polycarbides are metastable after decompression to ambient pressure.These experiments are accompanied by a cooperation with the Häussermann and Kohlmann groups (Stockholm and Leipzig, respectively), who are setting up a measuring stand for in-situ high-pressure experiments as part of an X-ray angstrom cluster project at the Petra III synchrotron in Hamburg. These complementary measurements would ideally provide the experimental parameters (pressure, temperature) that lead to successful syntheses in the LVP. Moreover, they would also allow the detection of products that would decompose again after decompression in the LVP.In addition to the studies on polycarbides, which would add another interesting facet to the already very rich structural chemistry of carbon (diamond, graphite, fullerenes, carbon nanotubes, graphene), we want to use the aforementioned setup to investigate how the oxidation power of carbon (graphite) changes under pressure. For other main group elements, including hydrogen, it has already been shown that oxidation of elemental platinum up to the +4 oxidation state is possible under pressure. Analogous investigations for carbon are unknown. But with the ternary acetylides Na2PdC2 and Na2PtC2, which we synthesised some time ago, ideal starting compounds would be available for these investigations.