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 P 2 1 / 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- d 4 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.