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

98 R.E. Meléndez · A.D. Hamilton
the development of a field known as synthetic supramolecular chemistry has
recently begun to emerge. Investigations on the assembly of small organic molecules
in solution and the solid state will be important in expanding these new
notions for the assembly of well-defined supramolecular architectures. The
purpose of this article is to review recent developments in the field of synthetic
supramolecular chemistry for the purpose of crystal engineering. We will place
particular focus on the use of intermolecular interactions to form tape, ribbon,
and sheet structures in the solid state.
2
Crystal Engineering and Molecular Recognition
The term crystal engineering was first coined by Schmidt in connection with his
work on the topochemical reactions of crystalline cinnamic acids in 1971 [1].
However, recently this field has developed rapidly due to its important implications
in materials science. Desiraju defines crystal engineering as “the understanding
of intermolecular interactions in the context of crystal packing and the
utilization of such understanding in the design of new solids with desired
physical and chemical properties” [2]. In this way crystal engineering, first
designed for solid state reactions, has been applied to the creation of solids that
exhibit properties such as nonlinear optical activity, ferroelectricity, piezoelectricity,
triboluminescence, and porosity.
Crystal engineering is based on concepts that have been broadly used in
supramolecular chemistry [3]. Crystals are not just collections of molecules and
their structural properties are different from those of their molecular constituents.
Crystals are a repetitive arrangement of molecules in three dimensions
with an impressive level of precision and have been regarded by Dunitz as
“supermolecules par excellence” [4].
A large amount of effort has been invested in the study of crystal growth [5,
6] and crystal packing [7]. The potential energy of a crystal has been factored
into component parts and has been attributed to various kinds of interactions
including, electrostatic, hydrogen bonding, donor-acceptor, steric repulsions,
and van der Waals attractions.While intermolecular interactions have been classified
in different ways, the most meaningful criteria are their distance dependence
and their directionality. Desiraju has classified intermolecular interactions
in organic solids into two types: medium-range isotropic forces (closepacking)
and long-range anisotropic forces (electrostatic interactions)
[8].Isotropic forces include C◊◊◊C, C◊◊◊H and H◊◊◊H interactions and anisotropic
forces include ionic interactions, strong hydrogen bonds ( O-H◊◊◊O, N-H◊◊◊O),
weak hydrogen bonds (C-H◊◊◊O, C-H◊◊◊N, O-H◊◊◊p) and other forces such as
halogen◊◊◊halogen interactions (see also the article by J.P. Glusker in this volume).
Non-covalent interactions have been extensively used in crystal engineering,
since they are the fundamental cause of the formation of crystals [4]. Hydrogen
bonding, p-p interactions, and p-hydrogen interactions have been used in particular
for this purpose. It is not our intention to describe every feature of the