The
achiral molecule 2-cyano-4,6-dimethylpyrimidine (Me2pmCN)
meets simple criteria that predict a supramolecular arrangement
capable of exhibiting plastic bending. Indeed, crystals grown by sublimation
bend readily without breaking under manual manipulation at room temperature.
Compression of a crystal perpendicular to the bending direction easily
“squashes” the crystal, a mechanical response akin to
metal-like malleability. Single crystal X-ray diffraction (XRD) study
reveals net alignment of the molecular dipoles propagating along the
21 screw axis in the monoclinic space group P21. Columnar π-stacked arrays of the planar molecules
extend in [100], the long axis of the crystals. Weak interactions
between the columnar structures account for the observed mechanical
behavior. Variable temperature powder XRD and differential scanning
calorimetry measurements of the plastic crystals indicate a solid-to-solid
phase transition from one crystalline phase to another at 80.7 °C
prior to melting at 83.3 °C.
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