![]() NMR is one of the most powerful tools for probing disorder in materials. ![]() This mean structure, however, does not fully describe structures containing disorder, and so complementary techniques are required to provide a more complete picture. Introduction Bragg diffraction provides information on the average periodic structure of crystalline materials. In addition, the unit cell enthalpies calculated after careful optimisations provide insight into why the disordered structure is adopted. This is just sufficient to observe a correlation between calculated and experimental linewidths, and also show that systematic errors associated with geometry optimisation do not compromise other applications of “NMR crystallography”. Careful optimisation is shown to reduce differences between 13C constants of symmetry-related sites to about 0.1 ppm. ![]() The limits of NMR crystallography calculations using density functional theory are tested by investigating how geometry optimisation conditions affect calculated NMR parameters. NMR linewidths in statically disordered systems reflect the distribution of local chemical environments, and this study investigates whether the disorder contribution to 13C linewidths can be predicted computationally. The caffeine molecules are disordered over two positions, with the nature of the disorder confirmed to be static by 13C solid-state NMR. The crystal structure of a new 1 : 2 caffeine–citric acid hydrate cocrystal is presented.
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