The effect of high pressure on the crystal structures of -, -and -glycine has been investigated. A new polymorph, δ-glycine, is obtained from  glycine. δ-Glycine is monoclinic, P2 1 /a, a = 11.156(4), b = 5.8644(11), c = 5.3417(17) Å,  = 125.83(4)° at 1.9 GPa. The transition, which occurs between 0 and 0.8 GPa, proceeds from a single crystal of -glycine to a single crystal of δ-glycine, resulting in an equal number of NH…O hydrogen bonds, but an increase in the number and strength of CH…O hydrogen bonds, which act to close-up of 'holes' which are formed within the layers of -glycine in the centers of R-type hydrogen bonded motifs. Trigonal -glycine begins to undergo a transition to another high-pressure phase, -glycine, at 1.9 GPa, but the transformation is destructive; it is essentially complete at 4.3 GPa. The structure is monoclinic Pn, a = 4.8887(10), b = 5.7541(11), c = 5.4419(11) Å,  = 116.682(10)° at 4.3 GPa. The structure consists of layers similar those observed in -glycine with inter-layer separations of 2.38 and 3.38 Å and CH…O interactions formed between the layers. Monoclinic -glycine is known to be stable to 23 GPa, and we have obtained a single crystal structure of this polymorph at 6.2 GPa. Super-short NH…O hydrogen bonds are not formed up to 6.2 GPa, and they only shorten significantly if they are formed parallel to CH…O hydrogen bonds which strengthen, or vectors across holes which close-up, under pressure.

The effects of high pressure on pharmaceutical compounds and energetic materials can have important implications for both the properties and performance of these important classes of material. Pharmaceutical compounds are frequently subjected to pressure during processing and formulation, causing interconversion between solid forms that may affect properties such as solubility and bio-availability. Energetic materials experience extremes of both pressure and temperature under conditions of detonation and deflagration, causing changes in properties such as sensitivity to shock and chemical reactivity. This tutorial review outlines the various methods used to study these materials at high pressure, describes how pressure can be used to explore polymorphism, and provides examples of compounds that have been studied at high pressure.

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The solid form screening of galunisertib produced many solvates, prompting an extensive investigation into possible risks to the development of the favored monohydrate form. Inspired by crystal structure prediction, the search for neat polymorphs was expanded to an unusual range of experiments, including melt crystallization under pressure, to work around solvate formation and the thermal instability of the molecule. Ten polymorphs of galunisertib were found; however, the structure predicted to be the most stable has yet to be obtained. We present the crystal structures of all ten unsolvated polymorphs of galunisertib, showing how state-of-the-art characterization methods can be combined with emerging computational modeling techniques to produce a complete structure landscape and assess the risk of lateappearing, more stable polymorphs. The exceptional conformational polymorphism of this prolific solvate former invites further development of methods, computational and experimental, that are applicable to larger, flexible molecules with complex solid form landscapes.

Explosives under pressurethe crystal structure of γ-RDX as determined by high-pressure X-ray and neutron di raction COMMUNICATION Swift et al. Structure of a lead urate complex and its e ect on the nucleation of monosodium urate monohydrate CrystEngComm www.rsc.org/crystengcomm