Te⋯I secondary-bonding interactions in crystals containing tellurium(II), tellurium(IV) and iodide atoms: supramolecular aggregation patterns, nature of the non-covalent interactions and energy considerations

This study delves into the intriguing realm of chalcogen-bonding interactions, specifically focusing on tellurium(II) and/or tellurium(IV) interactions with iodide species within six crystals. Utilising comprehensive computational chemistry calculations and underpinned by crystallographic data retrieved from the Cambridge Structural Database, this research elucidates the supramolecular aggregation, bonding nature and interaction energetics of Te & ctdot;I non-covalent bonds in a series of crystals containing each of tellurium(II), tellurium(IV) and iodide. The investigation encompasses a variety of molecular assemblies, ranging from zero-dimensional to complex three-dimensional architectures. Tellurium(II) atoms formed Te & ctdot;I interactions in six of the crystals but tellurium(IV) participated in Te & ctdot;I interactions in only three crystals despite there being equal numbers of tellurium(II) and tellurium(IV) atoms in the zero- and one-dimensional assemblies. Several computational tools, including Molecular Electrostatic Potential (MEP) surfaces, Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) analyses, provide a nuanced understanding of the electron density topology and charge transfer mechanisms. In some assemblies, where the Te & ctdot;I interactions are similar to 3.2 & Aring;, the interaction energies are very large, i.e. 25.6 to 38.8 kcal mol(-1), suggesting partial covalent character, an observation corroborated by the NBO analysis; longer Te & ctdot;I separations correlate with reduced energies, i.e. 3.1 to 7.0 kcal mol(-1). Crucially, it is noteworthy that the Te & ctdot;I interactions identified in this study are distinctly characterised as chalcogen bonds, rather than halogen bonds.