Crystals at a Carrefour on the Way through the Phase Space: A Middle Path

Abstract

Multiple supramolecular functionalities of cyclic α-alkoxy tellurium-trihalides (including Te---O, Te---X (X = Br, I) and Te---π(C=C) supramolecular synthons) afford rich crystal packing possibilities, which consequently results in polymorphism or Z’ > 1 crystal structures. Example of three crystal forms of cyclohexyl-ethoxy-tellurium-trihalides, one of which combines the packing of two others, affords a unique model to observe the supramolecular synthon evolution at the early stages of crystallization, when crystals on the way find themself at a carrefour between the evolutionally close routes, but fail to choose between two energetically close packing patterns, so taking the “middle path”, which incorporates both of them (and results in two crystallographically independent molecules). In general, this allows a better understanding of the existing structures, and an instrument to search for the new polymorphic forms.

Intermolecular Interactions Drive the Unusual Co-Crystallization of Different Calix[4]arene Conformations

“…Based on the peaks observed in the 13 C NMR, it was postulated that the cone conformation, 1c, was present [22,23], which is in line with previous conclusions drawn by van Loon et al into a structurally similar calix [4]diquinone structure [13]. The presence of the two conformers 1a and 1b in the crystal structure, and 1c in solution would suggest that 1 can readily interconvert between the conformations, most likely by an oxygen through the annulus mechanism, [24] and that solid state effects drive crystallization in the present form. This solution phase flexibility is in line with previous reports that calix [4]diquinones are generally more flexible than structurally similar 25,27-dialkoxycalix [4]arenes [11].…”

Quantitative Investigation of Intermolecular Te···A (A = π/Te/H) Interactions in Organotellurium Compounds from the Cambridge Structural Database

“…In tris (iodo)-(8-ethoxycyclo-oct-4-enyl)-tellurium ( OPUXAB ), the presence of a red spot between the interacting atoms Te and C, on the blue surface mapped with d norm , indicates the presence of an interaction with a contact distance ( d = 3.547 Å) less than the sum of their van der Waals radii (Figure (c)).…”

“…These spots suggest the presence of two symmetric Te•••π ChBs, with a contact distance (d = 3.532(6) Å) shorter than the sum of their van der Waals radii, as illustrated in Figure 9(b). Additionally, a light red spot appearing over another σ-hole signifies the formation of a Te•••Te ChB (d = 3.973(1) Å).In tris(iodo)-(8-ethoxycyclo-oct-4-enyl)-tellurium (OPUX-AB34 ), the presence of a red spot between the interacting atoms Te and C, on the blue surface mapped with d norm , indicates the presence of an interaction with a contact distance (d = 3.547 Å) less than the sum of their van der Waals radii (Figure9(c)).In 2,2′-ditellane-1,2-diylbis(5-bromo-4-methylpyridine) (XUTKED35 ), two deep red spots are observed between the interacting atoms Te and C on the blue surface, mapped with d norm , and they indicate the presence of two symmetric…”

Long-range supramolecular synthon polymorphism: a case study of two new polymorphic cocrystals of Ph2Te2–1,4-C6F4I2

“…In recent decades, the growing attention to non-covalent interactions has significantly expanded the crystal engineering toolkit 1–9 ‡‡See also CrystEngComm Themed Collections: “Halogen Bonding in Crystal Engineering Editor's collection, 2020”, “Halogen bonding: from self-assembly to materials and biomolecules, 2013”. and has sparked increased interest in cocrystals. 10–15 Directional, specific and tunable non-covalent interactions (especially σ- and π-hole 16,17 ones) make it possible to directly influence the packing of molecular cocrystals, expanding the structural landscape 17–22 of their components and allowing a deeper understanding of the fundamental molecular mechanisms of crystal formation. 23 In particular, this has led to a new level of consideration of the phenomenon of polymorphism.…”

“…23 In particular, this has led to a new level of consideration of the phenomenon of polymorphism. 19,24–26…”