With alkoxy groups
The crystal structures of E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,5-dimethoxybenzene,
have been determined. A weak intramolecular hydrogen bond between
protons on the olefinic link and the ortho-methoxy groups on
the adjacent benzene rings has been commented on. In general, however,
the crystal packing for these structures is primarily determined by
weak methoxy-pi interactions.
Their numbers change with the structure and length of the side chains
and with the accommodation of the extended chains in the lattice. A
discussion on the effects of these interactions on the possibility of
lattice formation explains why these four compounds crystallize and
several similar ones with different alkoxy side chains do not.
Vande Velde, C.M.L.; Chen, L.J.; Baeke, J.K.; Moens, M.; Dieltiens,
P.; Geise, H.J.; Zeller, M.; Hunter, A.D.; Blockhuys, F. Cryst.
Growth Des. 2004, 4, 823-830.
molecular symmetry is coincident with crystallographic inversion
symmetry. A three-dimensional network is generated containing both
CH...pi and CH...O
interactions. A comparison of the geometry of this molecule and the
structure of a number of 2,4,6-trimethoxy-substituted analogues is
Vande Velde, C.M.L.; Geise, H.J.; Blockhuys, F. Acta Cryst. C 2005,
crystallizes with one-half of a molecule in the asymmetric unit. A
three-dimensional network is generated by methoxy-pi and CH...pi interactions. The conformation of
the C-C bond exocyclic to the central benzene ring is different from
that of every other known derivative. A comparison of the geometry of (E,E)-2,5-dipropoxy-1,4-bis[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene
with other 2,4,6-trimethoxy-substituted PPV oligomers, in particular
the isopropoxy-substituted compound, is provided.
Vande Velde, C.M.L.; Baeke, J.K.; Geise, H.J.; Blockhuys, F. Acta
Cryst. C 2005, 61, o284-o287.
forms a packing that consists of an intricate network of both CH...O
hydrogen bonds and methoxy-pi interactions. The packing schemes of all
distyrylbenzenes are compared and explained on the basis of the
observations made made on E,E-1,4-bis[2-(2,4,6-trimethoxyphenyl)ethenyl]-2,3,5,6-tetramethoxybenzene.
In general, intramolecular CH...O contacts are
greatly preferred over intermolecular ones. Intermolecular
CH...O contacts are more common than intermolecular
methoxy-pi interactions. The
latter are adopted only when the number of free methoxy groups, not
involved in intramolecular CH...O contacts, is small enough.
Vande Velde, C.M.L.; Geise, H.J.; Blockhuys, F. Cryst. Growth
Des. 2006, 6, 241-246.
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,