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

Hydrogen-Bonded Ribbons, Tapes and Sheets as Motifs for Crystal Engineering 117
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Fig. 21. Tapes formed by complementary monomers 25 and 27
ality orientation. In monomers 28 and 29 (Fig. 22), the symmetry of the hydrogen
bonding groups is destroyed. As a consequence, the monomers can only
complement each other in a cyclic pattern. However, they are also self-complementary
and as a consequence recrystallization of the 1:1 complex rendered
crystals of compound 29 only, as seen in Fig. 22 [61].
2-Aminopyrimidine (30) has two hydrogen bond donors and two hydrogen
bond acceptors, which are all used in its crystal structure pattern (Fig. 23) [62].
Etter and Adsmond recognized that carboxylic acids have the appropriate
hydrogen bond functionality to form dimers with 30. Several mono- and di-carboxylic
acids were selected in this study to show the hydrogen bonding preference
of 30 to carboxylic acids rather than to itself [51]. The ribbons formed in
the crystal structure of 31, which is a 1:1 complex formed by 30 and succinic
acid, shows the extension of the motif formed by 30 (Fig. 23).
Our group has explored the hydrogen bond complementarity of carboxylic
acids and 2-amidopyridines. A series of bis(amidopyridine) derivatives 32
were synthesized to explore the recognition properties of dicarboxylic acids
33 (Fig. 24). When the dicarboxylic acid is of the correct size, a discrete hostguest
complex is formed (Fig. 24a). However, when the dicarboxylic acid is
increased in length the hydrogen-bonding ribbon motif is observed
(Fig. 24b–d) [18]. Furthermore, the relative orientation of the dicarboxylic
and bis(amidopyridine) derivatives could be controlled by varying their relative
length.
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