Long-Range Supramolecular Synthon Isomerism: Insight from a Case Study of Vinylic Tellurium Trihalides Cl(Ph)C=C(Ph)TeX₃ (X = Cl, I)

A slight modification of the synthetic procedure resulted in a new (Cc) polymorph of vinylic tellurium-trichloride Z-Cl(Ph)C=C(Ph)TeCl₃ (1, β-form) which is stabilized by Te· · · Cl chalcogen bonds, assembling its molecules into the zigzag chains. Such a packing motive is in contrast to the known (Pca2₁ ) polymorph of Z-Cl(Ph)C=C(Ph)TeCl₃ (1, α-form, CCDC refcode: BESHOW), which is built upon Te· · · π(Ph) chalcogen bonded chains. We noted a similar case of [Te· · · halogen] vs. [Te· · · π(Ph)] supramolecular synthon polymorphism in its triiodide congener Z-Cl(Ph)C=CPh(TeI₃ ) (2, α and β-polymorphic forms). Quantum chemical calculations of the intermolecular interaction and lattice energies for 1α–β and 2α–β supported the assumption that α is thermodynamic while β is a kinetic form. Kinetic forms 1β and 2β are isostructural (Cc), while the thermodynamic forms 1α (Pca2₁ ) and 2α (P2₁ /c) are not and feature an unusual example of long-range supramolecular synthon module isomerism. In other words, 1α–2α pairs demonstrate very similarly to isostructural Te· · · πPh ChB stabilized chains, which are further packed differently relative to each other, following different angular geometry of type-I Cl· · · Cl and type-II I· · · I halogen bonding. These structural considerations are backed by quantum chemical calculations that support the proposed hierarchy of primary and secondary supramolecular synthons and the assignment of α and β as thermodynamic and kinetic forms, respectively.