The initial proposal aimed to answer the question, whether sp3-carbonates, i.e. carbonates in which the carbon is tetrahedrally coordinated by four oxygen, are chemically and structurally as diverse as conventional carbonates. We have made significant progress to answer this question, but the major advance was due to the unexpected synthesis of the first inorganic pyrocarbonates, i.e. inorganic carbonates containing [C2O5]-groups, at moderate pressures and temperatures. This opened a new research field and we very successfully synthesized numerous pyrocarbonates. We also synthesized and characterized new conventional carbonates, such as Al-carbonate Al2[CO3]3, the first chemically simple anhydrous carbonate containing a trivalent metal cation that could be quenched to ambient conditions. The overarching goal of the continuation project is to establish a deeper crystal chemical and crystallographic understanding of stabilities and structure-property relations of anhydrous and hydrous sp3- and pyrocarbonates, and to synthesize new conventional anhydrous carbonates with trivalent metal cations. We will obtain the new phases by reactions, not by polymorphic transitions, which typically require much higher pressures and temperatures. The project is based on methodological, and on improvements of analysis software for single crystal diffraction data obtained from μm-sized samples in DACs. We propose to obtain the first anhydrous conventional REE-carbonates containing trivalent metal cations, where REE = La3+, Nd3+, Er3+, Lu3+, to complete our preliminary results on Fe3+- and Cr3+-carbonate and to attempt the synthesis of Sc3+-carbonate. We want to extend our studies of anhydrous alkali-pyrocarbonates, where we have obtained Li2[C2O5] and Na2[C2O5], to potassium, rubidium and cesium-carbonates. Furthermore, we have synthesized and characterized the first hydrous pyrocarbonate, Li[HC2O5], so we propose a systematic investigation of the formation of hydrous pyrocarbonates. Similarly, we have solved the structure of a first hydrous sp3-carbonate (Ba[H4C4O10][H3C4O10][H2CO3][HCO3]). Hence we aim to synthesize further high pressure sp3-carbonates. Finally, we propose to complete studies on systems for which we have obtained preliminary data in the first funding round. We have strong evidence for novel Mg-, Cr3+-, Be-, Ti-, and K-carbonates, but for these systems we either need a few more measurements or more time for the data analysis. Taken together, the expected results will allow us to establish a coherent encompassing model on the formation, stability and properties of conventional and novel carbonates.
DFG Programme
Research Grants
