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

Hydrogen-Bonded Ribbons, Tapes and Sheets as Motifs for Crystal Engineering 111
Based on Herbstein’s results using long chain guests, Zimmerman proposed
to prevent interpenetration of the trimesic acid networks by including a large
and relatively non-flexible guest molecule such as pyrene in the cavities. Indeed
the pyrene is incorporated in the cavity as well as some ethanol solvent molecules
(Fig. 13). The hydrogen bonded dimer in 2 is actually expanded by the presence
of ethanol molecules, although the formation of the hexamer prevails in
the sheet formation [48].
In the context of generating porosity, Zaworotko’s group has used a modular
approach in order to propagate the symmetry of trimesic acid. This strategy
involves the use of hydrogen bonding spacers between units of 2 to expand the
size of the cavities. In this case secondary amines were reacted with 2 to form
salts 15 and 16 (Fig. 14). The resulting solid lattices were observed in the crystal
b
a
= trimesate anion
= ammonium spacer
15
16
15
H 3TMA = trimesic acid (2)
Fig. 14 a, b. Schematic representation of the modular strategy for increasing cavity size in 2.
b Hydrogen bonding pattern in salts 15 and 16
16