The weak hydrogen bond in supramolecular chemistry

This chapter reviews the weak hydrogen bond in supramolecular chemistry by focusing on the relevance of these interactions in the analysis, design, and synthesis of the structures of molecular assemblies, most notably crystals. Supramolecular chemistry signifies chemistry beyond the molecule and deals with implications of the fact that molecules can recognise one another via intermolecular interactions, typically in condensed media. This field has grown into two distinct branches: the study of supermolecules in solution and in the solid state, mainly in crystal structures. The most important distinction between these two situations is not structural but lies in the lifetime of the interactions − supramolecular association in the crystal is time-stable whereas in solution it is not. The present chapter mainly concentrates on solid-state supramolecular systems, and discusses the role of weak hydrogen bonds in inclusion complexes such as crown ethers, oligoaryl hosts, and cyclodextrins (cycloamyloses). The promises and problems of crystal engineering are also considered, together with drug design and biological recognition.