Solvent inclusion in the crystal structure of bis[(adamantan-1-yl)methanaminium chloride] 1,4-dioxane hemisolvate monohydrate explained using the computed crystal energy landscape

Repeated attempts to crystallize 1-adamantanemethylamine hydrochloride as an anhydrate failed but the salt was successfully crystallized as a solvate (2C11H20N⁺·2Cl^-·0.5C4H8O2·H2O), with water and 1,4-dioxane playing a structural role in the crystal and engaging in hydrogen-bonding interactions with the cation and anion. Computational crystal-structure prediction was used to rationalize the solvent-inclusion behaviour of this salt by computing the solvent-accessible voids in the predicted low-energy structures for the anhydrate: the global lattice-energy minimum structure, which has the same packing of the ions as the solvate, has solvent-accessible voids that account for 3.71% of the total unit-cell volume and is 6-kJ-mol^-1 more stable than the next most stable predicted structure.