Polymorphism, structure, guest conformation, and dynamics in the inclusion compound of 1,2-dichloroethane with tris(5-acetyl-3-thienyl) methane : a combined single crystal and powder X-ray diffraction, 13C CP/MAS, and 2H NMR study

Various physicochemical characterization techniques were used to study the structure and guest dynamics of the 1,2-dichloroethane/tris (5-acetyl-3-thienyl) methane (TATM) inclusion compound. This complex was observed to crystallize in two forms, a triclinic P-1 structure and a less usual monoclinic P21/c form. The X-ray structures indicate that the TATM molecules form "bottleneck" channels parallel to the crystallographic c axis in both forms and that the guests exist exclusively in the trans form. Solid-state deuterium NMR spectroscopy was used to study the dynamics of the 1,2-dichloroethane-d4 guest in the triclinic form. The simplest model consistent with the experimental NMR spectra was based on internal rotation about the C-C bond (a trans/gauche conformational equilibrium). As this was not consistent with the X-ray structure, another model was developed where the trans conformer performs 180 flips about an axis through the center of symmetry of the guest and perpendicular to the Cl-C-C-Cl plane. The important point to be taken from this work is that complementary methods are often necessary to discriminate between motional models based on a single technique, and that the simplest model is not necessarily correct.Peer reviewed: YesNRC publication: Ye