198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

120 R.E. Meléndez · A.D. Hamilton
3.3
Other Strong Hydrogen Bonds
Etter et al. showed the formation of a cyclic hexamer when 1,3-hexanedione (34)
is cocrystallized with benzene or deuterated benzene. The beauty of this work is
that the hexamer aggregate is only formed when the guest solvent molecules are
present. The crystal structure of 1,3-hexanedione forms a tape in the absence of
guest (Fig. 25) [63].
Aoyama et al. have also developed the use of N-H◊◊◊O hydrogen bonds to
generate sheet structures [64]. They also take advantage of the p-stacking interactions
of the molecules to control the supramolecular architecture of the solid.
Compounds 35 and 36 cocrystallize to give a sheet held together by strong
hydrogen bonding (Fig. 26). These controlled crystal lattices possess some
selectivity in their inclusion of small molecules [65] and have even been shown
to catalyze bimolecular Diels-Alder reactions within the pores [66] (more details
are given in the article by Y. Aoyama in this volume).
Amidinium cations are interesting functional groups for the purpose of
crystal engineering. Hosseini et al. have applied amidinium 37 in the design of
tapes using the fumarate dianion 38 as a spacer [67]. In the crystal structure the
tapes are linked together by fumaric acid spacers therefore propagating into
sheets (Fig. 27).
a
b
34
Fig. 25 a, b. Compound 34 forms: a tapes in the absence of guest; b cyclic hexamers in the
presence of guest such as benzene