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With methoxy groups
Four new methoxy-substituted derivatives of E,E-2,5-bis(2-phenylethenyl)pyrazine
have been synthesized. The supramolecular structures of the resulting
set of five polymorphs have been studied using single-crystal X-ray
diffraction to gauge the influence of the position of the methoxy groups
on the organization of the molecules in the solid state, as part of an
attempt to dispense with the particular polymorphism of the parent
compound. The crystal packing patterns were analyzed in terms of the two
pyrazine-based synthons found in the parent compound's crystal
structure, the pi(pyrazine)...pi(phenyl) stacking synthon, and the
pyrazine hydrogen-bonded synthon, as well as in terms of weak
intermolecular interactions such as CH...O, CH...N, and CH...pi. The
analysis shows that the introduction of methoxy groups in positions
other than only the para position of the peripheral benzene rings
successfully switches off the two synthons seen in the parent compound
and that the new compounds adopt other packing strategies, based on
methoxy...methoxy and –OCH3...pi contacts. Polymorphism, however, remains.
Collas, A.; Bagrowska, I.; Aleksandrzak, K.; Zeller, M.; Blockhuys, F. Cryst. Growth Des. 2011, 11, 1299-1309.
With fluorine atoms
Three derivatives of E,E-1,4-bis[2-(2,3,4,5,6-pentafluorophenyl)ethenyl]benzene,
two of which bear nitrogen atoms in the ethenyl spacers, while in a
third the central benzene ring is replaced by a pyrazine moiety, have
been synthesized. The supramolecular structures of the resulting set of
four compounds have been studied using single-crystal X-ray diffraction
to gauge the influence of the position of the nitrogen atoms on the
organisation of the molecules in the solid state. The crystal packing
patterns were analyzed in terms of intermolecular interactions involving
the fluorine and nitrogen atoms, i.e., CH...F, F...F, F...pi and
CH...N interactions. The analysis shows that in two of the three
solid-state structures the main effect of the nitrogen atoms in an
indirect one: they do not participate in intermolecular contacts
themselves, but activate nearby hydrogen atoms and phenyl rings in
fluorine synthons to form new interactions.
Collas, A.; De
Borger, R.; Amanova, T.; Blockhuys, F. CrystEngComm 2011, 13,
702-710.
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