Crystal Growth & Design
Article
essentially rigid, planar species that cannot adopt conforma-
tional chirality nor does it fit the description of a banana-
shaped44 or bent-core45 achiral molecule. The columnar arrays
are not helical or propeller-like. The origin of the chirality arises
from a combination of different tilt angles of the two molecules
in the asymmetric unit and a 21 screw axis in the direction
aligning the molecular dipoles.
ACKNOWLEDGMENTS
■
K.E.P. acknowledges the Natural Sciences and Engineering
Research Council (NSERC) of Canada for a Discovery Grant
(DG), the government of Canada for a Tier II Canada Research
Chair (Chemistry of Molecular Materials), and the Canada
Foundation for Innovation John R. Evans Leaders (CFI-JELF)
Fund and the Ontario Research Fund (ORF) for funding the
PXRD infrastructure. D.V.S. thanks the Canada Foundation for
Innovation (CFI) for funding the single crystal X-ray diffraction
facility and NSERC for funding for the DSC Analyzer.
CONCLUSION
■
Me2pmCN crystallizes as colorless needles in the space group
P21. These needles exhibit plastic bending properties at
ambient temperature, a phenomenon that can be correlated
to the observed crystal-packing motif. Moderate π-stacking
interactions, which serve to create columns of molecules in
[100], are significantly stronger than very weak intercolumnar
interactions in at least one direction. The mutually
perpendicular stronger and weaker interactions in the crystal
structure enable bending without breaking in response to
pressure applied perpendicular to the long axis of the crystal.
An unusual mechanical response to compression along the
length of the crystal (perpendicular to (100)) is observed,
wherein a crystal can be “squashed”, similar to crumpling an
empty soda can. Interestingly, DSC data suggest a lack of
significant change in microscopic crystalline morphology upon
mechanical manipulation. Multiple measurements of visually
flawless single crystals, highly bent crystals, crushed crystals,
and gently ground samples all exhibit a comparable DSC
response, indicating a high temperature crystal-to-crystal phase
transition followed by melting. The alignment of molecular
dipole moments within the crystal also suggests a possible
piezoelectric response to mechanical pressure. This will be
investigated as it relates to the plastic mechanical properties of
the crystal.
ABBREVIATIONS
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DSC, differential scanning calorimetry; XRD, X-ray diffraction;
PXRD, powder X-ray diffraction; CIF, crystallographic
information file; CCD, charge coupled device; DMSO,
dimethyl sulfoxide; Me2pmCN, 2-cyano-4,6-dimethylpyrimi-
dine; vdWr, van der Waals radii
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ASSOCIATED CONTENT
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AUTHOR INFORMATION
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Corresponding Authors
ORCID
Notes
The authors declare no competing financial interest.
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Cryst. Growth Des. XXXX, XXX, XXX−XXX