High-Resolution X-ray Diffraction of Te ^II -Centered Chalcogen Bonds: Direct Visualization of σ–Holes and Quantitative Bonding Analysis

Despite the well-established importance of chalcogen bonding in crystal engineering and supramolecular chemistry, experimental charge density data for TeII-centered chalcogen bonds have remained entirely absent, leaving the electronic nature of these interactions uncharacterized at the level of directly measured electron density. Here, we report the first high-resolution X-ray diffraction (HRXRD) study of TeII-centered chalcogen bonds, using cocrystals of bis(2,3,5,6-tetrafluoropyridin-4-yl)telluride (Py2FTe) with 1,4-diazabicyclo[2.2.2]octane (DABCO) as a model system; the isostructural S and Se analogues provide a comparative framework across the chalcogen series. Multipole refinement against the HRXRD data yields three findings reported here: direct experimental visualization of the σ–hole on a TeII site via static deformation electron density maps; unambiguous QTAIM-based classification of the TeII···N chalcogen bond as partially covalent (1 < |V|/G < 2) and the TeII···F contact as purely electrostatic (|V|/G < 1); and a quantitative experimental reference for benchmarking DFT methods, with PBE-D3/jorge-DZP-DKH identified as the recommended protocol for heavy-chalcogen σ–hole systems. These results establish a charge density foundation for the rational design of Te-based supramolecular architectures and provide experimental validation of the partially covalent character of TeII-centered chalcogen bonding.