The accurate determination of the interactions that play an important role in
the formation of molecular assemblies is an essential step in the process of
design and synthesis of new (supra)molecular compounds and materials.
The key-techniques for the design of new crystalline materials are
single-crystal and powder diffraction in combination with other methods
like (solid state) NMR, HPLC, IR, DSC, TGA etc. This field of research, design of new (crystalline) materials, with specific properties, on the basis of information on molecular interactions, is called Crystal Engineering. Recently, a new journal, Crystal Engineering, started to report on this rapidly emerging field.
A recent crystal engineering project in Nijmegen involved the study of inclusion compounds of cephalosporin antibiotics. Inclusion compounds, like clathrates, only exist in the solid state. X-ray diffraction (on powders and single crystals) is a very powerful tool to examine this type of compounds and in combination with molecular modelling and chemometrical approaches it was possible to find new non-toxic guest molecules which form complexes with the antibiotics very efficiently and selective. An efficient complexation of host molecules is an important technique in the isolation of chemical compounds from mixtures of molecules.
Research on co-crystallizing compounds is a good strategy for obtaining insight into molecular interactions and molecular recognition. Such insight may be of significant interest for co-crystallization of supramolecular compounds in order to obtain a crystalline state which would otherwise not be accessible. The approach we have chosen for studying a specific group of complexes can easily be applied to other systems and therefore we wish to continue this theme in the future.