The Cambridge Structural Database has been used to investigate the detailed environment of water molecules, hydrogen bonded to oxygen and nitrogen atoms, within molecular crystal hydrates. Eight coordination states of water have been investigated for 3315 structures, and hydrogen bond length and angle data were obtained and analyzed. The two most common environments are those in which water forms either three or four hydrogen bonds to neighboring molecules.

This contribution concerns the issue of crystal nucleation in the polymorphic and hydrate forming system inosine-water. A combination of computational and experimental tools have been used to explore the relationship between solution phase inosine species and the structural synthons as found in its crystal structures. It is evident that the initial nucleation of a metastable polymorph at temperatures above 10 degrees C is directed by dimeric self-association as revealed through proton NMR. At lower temperatures a dihydrate structure becomes the most stable solid phase and in this region of the phase diagram this is the only form that appears even though the solution species remain unchanged. This can only be rationalised in terms of a combination of water binding to the solution dimers and the thermodynamic stability of the hydrate crystal structure.

† Electronic supplementary information (ESI) available: synthesis details for 1-4, crystal refinement details and colour structures for 1, 2 and 4. See

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