Interplay between Inter- and Intramolecular Halogen-/Chalcogen-Bonding in Two-Molecule Aggregates Featuring Te^II···I...

The Cambridge Structural Database (CSD) was searched for crystals containing both tellurium(II) and iodine, revealing ten molecular crystals featuring distinct two-molecule aggregates encompassing Te···I interactions. These supramolecular assemblies were classified into three categories based on their geometric characteristics: halogen bonds (HaB), chalcogen bonds (ChB), and Type I interactions. A systematic structural comparison with lighter congeners (substituting Te with Se, S, and I with Br, Cl, and F) highlighted the exclusive propensity of tellurium and iodine to form these specific motifs, often with limited isostructurality across the series. To provide deeper insight into the nature of these noncovalent interactions, Density Functional Theory (DFT) calculations (PBE0-D3/def2-TZVP) were conducted on five representative systems. The computational results, including Molecular Electrostatic Potential (MEP) surfaces, QTAIM, and NBO analyses, revealed that the supramolecular organization is governed by a delicate interplay between the nature of intermolecular Te···I contacts and additional Te···N, O, S, and Te contacts, intramolecular or external, which are classified as ChBs exclusively. The energetic analysis demonstrated that while some aggregates are driven by robust HaBs, others rely on the cooperative effects of weaker ChBs and auxiliary interactions, with substantial orbital charge transfer contributions confirmed by NBO analysis.