When are organic crystals likely to absorb water and can we predict this phenomenon?

What is it about?

Crystal engineering relies on logical structural descriptors such as hydrogen bond donors and acceptors to explain why organic molecules form complex structures. But we still don't understand the ubiquitous nature of water in crystallization and why some molecules easily hydrate even when an organic solvent is used in experiments whilst others do not even when water is used as the solvent of crystallization. Here we show that mapping the % solvent accessible voids in the predicted crystal structures of hydrochloride salts can be a useful complement to experimental crystallization screens in providing a qualitative assessment of the potential for organic salts to hydrate.

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Why is it important?

Most crystal structure prediction studies are limited to calculating the relative lattice energies of predicted structures. However, we show here that there is much more useful information we can gather from the computed crystal energy landscape than just the relative energies of predicted structures. In particular we show for the first time that the propensity for crystal hydration in hydrochloride salts can be understood on the basis of the packing efficiencies of the predicted low energy structures.

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