The importance of technetium in radiochemistry ranges from radiopharmaceutical applications all the way to nuclear waste. In addition to these application-related fields, the central position of the element in the periodic table makes the chemistry of technetium an essential tool for answering general chemical questions regarding the understanding of reactivity, structure and property relationships between elements of the d-block. In this context, we study the molecular chemistry of technetium systematically. Experiments are conducted using the long-lived, weakly β^- emitting isotope ⁹⁹Tc. As one of the major fission products of uranium, the nuclide accumulates in spent nuclear fuel by decay of initially formed ⁹⁹Mo via ^99mTc making it available in macroscopic amounts. Our research interests span from simple inorganic ligands (e.g. oxido, nitrido or nitrosyl ligands) via classic organometallic ligands (e.g. carbon monoxide, alkyls, aryls, alkenes, alkynes or hydrides) to complex ligand systems that could be promising candidates for applications in nuclear medicine. The objective is to provide well-evidenced insights about the bonding properties, structure and stability of the formed complexes. Explicitly, also model systems enabling a systematic investigation of the interaction between technetium and its ligands in comparison to neighboring elements such as Mn, Re, Mo, W, Fe, Ru or Os are developed. The systematic data and the derived conclusions shall represent reliable references to assist the understanding of the complex speciation of technetium in different application-oriented fields.

A special focus point is the systematic correlation of spectroscopic properties with the structure of technetium compounds. Modern spectroscopic infrastructure such as nuclear magnetic resonance (NMR) spectroscopy, attenuated total reflection infrared spectroscopy (ATR-IR) or advanced X-ray spectroscopy (e.g. XANES/EXAFS) as well as single crystal X-ray diffraction are available directly at INE or at neighboring institutes. They are complemented by density functional theory (DFT) or quantum chemical ab initio calculations. This interdisciplinary approach allows the comparative characterization of technetium compound and to precisely quantify the subtle, but for the chemistry of the element essential, differences of interactions between the metal and its ligands. A key concept is the coupling of single-crystal diffractometry, ⁹⁹Tc NMR spectroscopy and X-ray absorption spectroscopy (e.g. XANES/EXAFS) with theoretical methods. ⁹⁹Tc NMR spectroscopy allows the detection of NMR directly at the transition metal nucleus. The large nuclear spin of 9/2 partially counteracts the significant quadrupolar moment and the ⁹⁹Tc resonances of technetium compounds show comparably narrow lines for a quadrupolar nucleus (10 Hz-20 kHz). The isotopic purity of ⁹⁹Tc used in the experiments and the resulting good NMR receptivity (about 86 relative to ¹H) make ⁹⁹Tc NMR spectroscopy a highly specific method for investigating the chemical environment of diamagnetic technetium compounds.

Studies on the fundamental chemistry of technetium are conducted in a cooperation led by the independent junior research group leader Dr. Maximilian Roca Jungfer through a Liebig fellowship of the Fonds der Chemischen Industrie. The investigations are integrated into different national and international as well as university internal collaborations.

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