Energy matters

The delicate balance between a variety of energetic factors in molecules and crystal structures is reflected in the molecular and intermolecular geometry determined by X-ray diffraction methods. This balance is most clearly observed in the energetically soft parameters: torsion angles that define conformation and the distances and angles that define intermolecular interactions and molecular aggregation in the crystalline state. This review stresses the importance of the geometry-energy relationship as an aid to our interpretation of individual crystal structures, and discusses the transferability of systematic information derived from crystal structures to other phases and to other application domains, such as drug discovery and materials development.