Crystal engineering is the design and synthesis of molecular solid-state structures with desired properties, based on an understanding and exploitation of intermolecular interactions. The two main strategies currently in use for crystal engineering are based on hydrogen bonding and coordination complexation. These may be understood with key concepts such as the supramolecular synthon and the secondary building unit.
Crystal engineering relies on noncovalent bonding to achieve the organization of molecules and ions in the solid state. Much of the initial work on purely organic systems focused on the use of hydrogen bonds, though with the more recent extension to inorganic systems, the coordination bond has also emerged as a powerful tool. Other intermolecular forces such as π…π, halogen…halogen, and Au…Au interactions have all been exploited in crystal engineering studies, and ionic interactions can also be important. However, the two most commonly used strategies in crystal engineering exploit hydrogen bonds and coordination bonds.
Molecular self-assembly is at the heart of crystal engineering, and it typically involves an interaction between complementary hydrogen-bonding faces or a metal and a ligand. By analogy with the retrosynthetic approach to organic synthesis, Desiraju coined the term "supramolecular synthon" to describe building blocks that are common to many structures and hence can be used to order specific groups in the solid state. The carboxylic acid dimer represents a simple supramolecular synthon, though in practice this is only observed in approximately 30% of crystal structures in which it is theoretically possible. View More
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