Decreased Crystal Plasticity by Solvation - the Case of Levofloxacin Acesulfame

A correlation between crystal packing efficiency and plasticity can be used to efficiently rank the order of plasticity of crystal forms of a compound from their crystal structures. It was hypothesized that a lower crystal packing efficiency and density lead to higher plasticity of a hydrate. This hypothesis was only supported by the observation that stoichiometric hydrates exhibit both higher plasticity and lower packing efficiency than the corresponding anhydrates. In this work, we have tested this hypothesis using a channeled hemimethanol solvate of a levofloxacin acesulfame salt. Our results strengthen the hypothesis since, compared to the isostructural anhydrate, the hemimethanol solvate exhibits both higher packing efficiency and lower plasticity. The lower plasticity of the solvate is confirmed by crystal structure analysis and energy framework calculations. If this correlation between crystal packing efficiency and plasticity is robust, then we can objectively predict material plasticity of structurally related crystals based on crystal packing efficiency.