Mechanical properties of molecular crystals—applications to crystal engineering

Abstract

Image reproduced with permission from Abbie TrewinOther articles published in this issue include:Dipyrrin based homo-and hetero-metallic infinite architectures Stéphane A. Baudron, CrystEngComm, 2010,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 twodimensional 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.

Application of instrumented nanoindentation in preformulation studies of pharmaceutical active ingredients and excipients

“…Review articles and handbooks provide a good starting point for basic principles of the method (35,38,39,(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61). However, it is the author's experience that there is a common set of misconceptions and errors in the application of nanoindentation in pharmaceutical technology.…”

“…Plastic deformation due to twinning occurs in crystals with low symmetry and few slip systems or when plastic deformation is obstructed due to unfavorable alignment or under high loads. Unlike slip, twinning deformation is homogenous over the entire crystal lattice and is not restricted to multiples of the lattice parameter (45,46,50,58,(92)(93)(94)(95). Compounds with a disordered, corrugated layered structure do not show shearing; they bend or break under applied mechanical stress.…”

Understanding the role of vibrations, exact exchange, and many-body van der Waals interactions in the cohesive properties of molecular crystals

“…1 For these reasons alone the prediction of molecular crystal structures is of the utmost importance. 2 In addition, molecular crystals can also have a wide range of optical, electronic, and mechanical properties, 3 which in some cases can be tuned based on environmental variables 4 or composition. 5 The importance of molecular crystals has lead to various computational approaches being employed to understand and elucidate their properties.…”

The Elusive Structural Origin of Plastic Bending in Dimethyl Sulfone Crystals with Quasi‐isotropic Crystal Packing

“…The quest for novel organic compounds that can substitute for inorganic materials has motivated material chemists to explore the physical properties of organic solids.A mong the various properties,t he mechanical behavior of organic crystals has gained considerable attention recently.A part from the fact that mechanical properties are directly relevant to several aspects of solid state sciences [1] (such as formulation of drugs in the pharmaceutical industry [2] and devising organic functional materials [3] ), these properties point to certain fundamental structural connections with the nature and strength of the interactions between molecules in the crystals. While most organic crystals are known to be brittle,n ewer examples of crystals that exhibit plastic and elastic bending are being discovered.…”