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

Supramolecular Synthons and Pattern Recognition
Ashwini Nangia · Gautam R. Desiraju
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
E-mail: grdch@uohyd.ernet.in
The aims of crystal engineering are the understanding of intermolecular interactions and
their application in the design of crystal structures with specific architectures and properties.
In general, all types of crystal structures may be considered but this article is limited to
organic molecular solids. Because of the molecular basis of organic chemistry, the obvious
question arises as to whether there are simple connections between the structures of molecules
and the crystals that they form. Answers to such questions may be found through a better
and more comprehensive understanding of the interactions that control crystal packing.
These interactions include strong and weak hydrogen bonds. Patterns of interactions, such as
would be useful in a predictive sense, can be obtained by manual inspection or more rigorously
with the use of crystallographic databases. Such patterns are termed supramolecular
synthons and they depict the various ways in which complementary portions of molecules
approach one another. The identification of synthons is then a key step in the design and
analysis of crystal structures. Such ideas are also important in the understanding of phenomena
such as biological recognition and drug-enzyme binding. Pattern identification also
leads to the possibility of comparison of crystal structures. The use of the supramolecular
synthon concept facilitates such efforts and in this regard it may be mentioned that synthons
combine topological characteristics with chemical information, thereby offering a simplification
that is optimal to drawing such comparisons.
Keywords: Hydrogen bond, Supramolecular synthesis, Molecular recognition, Structure comparison,
Structure prediction.
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
2 Crystals as Supermolecules . . . . . . . . . . . . . . . . . . . . . . . 59
3 Supramolecular Synthons and Networks . . . . . . . . . . . . . . . . 60
4 From Organic Synthesis to Crystal Engineering . . . . . . . . . . . . 63
4.1 Connection Between Molecular and Crystal Structure . . . . . . . . 65
4.2 Goals and Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 The Cambridge Structural Database (CSD) . . . . . . . . . . . . . . 71
6 Multipoint Recognition Patterns . . . . . . . . . . . . . . . . . . . . 73
Topics in Current Chemistry, Vol. 198
© Springer Verlag Berlin Heidelberg 1998