Chalcogen bond-driven self-assembly of a 4-tert-butylcalix[4]arene-ebselen conjugate

The structural and self-assembling traits of a molecular system are intricately linked to the complex interplay of weak non-covalent interactions that exist within the molecule (intramolecular) and with other molecules (intermolecular). In this work, we report the interplay of intra- and intermolecular chalcogen bonds (i.e., Se⋯O) on the conformational and self-assembly attributes of a 4-tert-butylcalix[4]arene-ebselen conjugate (or compound 1). Compound 1 was crystallised into two distinct conformational polymorphs: 1' (sc, sc) and 1″ (sc, ap). Crystallographic studies have shown that both polymorphs assume 1D polymeric chains in which the repeat units are glued via Se⋯O chalcogen bonding. The differential scanning calorimetry profile of amorphous solid 1 indicated a clear glass transition and subsequent melting, with the corresponding glass transition temperature (T_g) and melting temperature (T_m). Powder X-ray diffraction studies on amorphous samples (obtained from CHCl₃) and crystalline samples (obtained from CHCl₃ : MeOH) revealed that MeOH plays a structure-directing role in the self-assembly process. Computational and crystallographic studies show that a weak chalcogen bond between the ethereal O and Se plays a conformational control role, whereas a strong chalcogen bond between the amide O and Se governs self-assembly.