Crystallography (ref.1), (ref.2), is one of the most powerful technique for studying the structure of solid matter at the atomic scale. The determination of the atomic structure of a crystal is most often carried out by single crystal X-ray diffraction. This technique makes it possible to obtain the exact position of the atoms within a material. In the case of molecular materials, we have access not only to the three-dimensional structure of the molecule, but also to its environment (interactions with neighboring molecules).
Structural x-ray diffraction analysis on single crystals therefore provides invaluable information in various fields of science: physics, chemistry, biology, medicine, and so on. Thus, for example, it has been involved in the discoveries of the double helix structure of DNA (Nobel of Medicine in 1962) and other important biochemical substances (Nobel of chemistry in 1964). The crystallography reveals the intimate structure of the organized material and allows to explain the properties of these and to imagine new materials.
Indeed, the field of crystal engineering concerns "the design and synthesis of molecular solid state structures with desired properties, based on an understanding and use of intermolecular interactions". For example, researchers have developed, with the control of hydrogen bond (HB) or halogen bonds (XB), porous materials (molecular tectonics) that can be used to carry out a catalytic reaction or to perform the separation of molecules. (Ref 1, Ref 2, Ref 3, Ref 4, Ref 5, Ref 6) They also used these same interactions to design new drugs by studying the crystal structure of receptor-ligand complexes. (ref.1, ref.2, ref.3)