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,
With nitro groups
Two polymorphs of (E,E)-N,N'-bis(4-nitrobenzylidene)benzene-1,4-diamine have been identified. In each case, the molecules lies across a crystallographic inversion centre. the supramolecular structure of the first polymorph features stacking based on pi...pi interactions assisted by weak hydrogen bonds involving the nitro groups. The second polymorph displays a perpendicular arrangement of molecules linked via the nitro groups, combined with weak CH...O hydrogen bonds. Both crystal structures are compared with that of the carbon analogue (E,E)-1,4-bis[(4-nitrophenyl)ethenyl]benzene.
Collas, A.; Zeller, M.; Blockhuys, F. Acta Cryst. C 2011, 67, o171-o174.
With methoxy groups
The solid-state structures of three push-pull acceptor-pi-donor (A-pi-D) systems differing only in the nature of the pi-spacer have been determined. (E)-1-nitro-4-[2-(3,4,5-trimethoxyphenyl)ethenyl]benzene and its 'bridge-flipped' imine analogues, (E)-3,4,5-trimethoxy-N-(4-nitrobenzylidene)aniline and (E)-4-nitro-N-(3,4,5-trimethoxybenzylidene)aniline, display different kinds of supramolecular networks, viz. corrugated planes, a herringbone pattern and a layered structure, respectively, all with zero overall dipole moments. Only the latter crystallizes in a noncentrosymmetric space group and is, therefore, a potential material for second-harmonic generation (SHG).
Collas, A.; Blockhuys, F. Acta Cryst. C 2011, 67, o364-o369.