Mechanical properties of molecular crystals—applications to crystal engineering

We present an overview of very recent advances in the understanding of structure–mechanical property correlations in molecular crystals. After the introductory part on some classical two-dimensional structures from the literature, we survey recent reports (mostly since 2005) pertinent to the mechanical properties of molecular crystals studied by application of external stress using a range of techniques. This includes both qualitative (shearing, bending and brittle crystals) and quantitative (nanoindentation, powder compaction and high-pressure) studies on establishing the correlation of anisotropic mechanical behaviour with the underlying crystal structure. Section 9, emphasizes on the usefulness of crystal engineering approach to improve the mechanical properties of molecular crystals, particularly the active pharmaceutical ingredients for their better tabletability properties. The parallels of the phenomena in other class of well studied materials are also appropriately drawn and discussed in the context of structure-mechanical property relationship. In the final part we comment on the prospects and ramifications of this emerging field.