Molecular Recognition, Complementarity and Self-Assembly

7 The Three-Dimensional Template Effect, Supramolecular Chemistry and Molecular Topology 

Some of the simplest selective systems are based on hydrogen bonding interactions between molecules. Carboxylic acids hydrogen bond to form dimers (Fig. 7-24), although this process is relatively unselective in the absence of other interactions. The interaction is described as self-complementary - the carboxylic acid functionality contains both the carbonyl oxygen atom as a donor and the hydrogen atom as the acceptor. 

If two or more such carboxylic acid groups are present in a molecule, intricate solid-state structures may be assembled, as seen in the ribbon-like solid state structure of terephthalic acid (7.41). 

With carboxylic acids, the simple dimeric species are reasonably persistent in solution (and the gas phase), but the more extended structures are generally limited to the solid state. Hydrogen bonding between carbonyl oxygen atoms and amino N-H groups has 

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