Conformational trimorphism of bis(2,6-dimesitylphenyl)ditelluride

Abstract

Besides the previously known α-form (monoclinic, P21/c, Z=4) of bis(2,6-dimesitylphenyl)ditelluride, two new polymorphic modifications, namely the β-form (monoclinic, P21/c, Z=8) and the γ-form (triclinic, P1̅, Z=2), were obtained serendipitously during chemical reactions. In all three modifications, the individual molecules possess significantly different conformations and bond parameters, such as Te–Te bond lengths, C–Te–Te bond angles, C–Te–Te–C torsion angles and intramolecular Menshutkin interactions, which is also reflected in their non-covalent interactions with adjacent molecules in the crystal lattice via London dispersion and electrostatic forces. The interplay between intermolecular and intramolecular forces in these conformational polymorphs was investigated using quantum chemical calculations, which reveal that the β-form should be thermodynamically stable at absolute zero. In contrast, crystallization experiments and thermoanalytical investigations indicate that the α-form is stable at high temperatures and therefore, both forms might be related by enantiotropism.

Low and High Z′ Polymorphs of Dibenzyldiphenylsilane: A Hydrocarbon-Patterned Molecular Crystalline System

“…26−29 Studies on polymorphism and high Z′ structures in molecular crystals have mainly been carried out on organic compounds that are capable of forming comparatively strong and directional hydrogen bond networks, 30,31 which is often due to the better reproducibility and predictability of the crystal structures. 32−37 The importance of weak intermolecular interactions as a crucial structure-determining factor for distinct crystal packing arrangements has become particularly evident in the context of conformational polymorphism 31,38,39 and through the observation of uncommon polymorphic systems. 40,41 The latter refers, for example, to polymorphs with conserved hydrogen bonds 40 or to polymorphs that exchange strong hydrogen bonds for weak interactions.…”

“…Crystal structure prediction and the design of functional crystalline materials with special chemical or physical properties (crystal engineering) are still one of the greatest challenges in condensed matter science. , Crystalline polymorphism in molecular crystal structures − is often associated with the phenomenon of multiple molecules in the crystallographic asymmetric unit ( Z′ > 1), − and considerations about the origins of high Z′ structures still give rise to controversial debates. , Polymorphism has always been the subject of considerable attention not only because of a purely intrinsic crystallographic interest but also because of its great importance in pharmaceutical science, − for patent protection in drug manufacturing, and for photofunctional and semiconducting materials. − Its appearance unmistakably reveals the complexity of crystallization processes. − Studies on polymorphism and high Z′ structures in molecular crystals have mainly been carried out on organic compounds that are capable of forming comparatively strong and directional hydrogen bond networks, , which is often due to the better reproducibility and predictability of the crystal structures. − The importance of weak intermolecular interactions as a crucial structure-determining factor for distinct crystal packing arrangements has become particularly evident in the context of conformational polymorphism ,, and through the observation of uncommon polymorphic systems. , The latter refers, for example, to polymorphs with conserved hydrogen bonds or to polymorphs that exchange strong hydrogen bonds for weak interactions . However, molecules that consist entirely or essentially of an aromatic or aliphatic hydrocarbon skeleton have much less frequently been the subject of systematic investigations.…”