The nanocrystalline αII-phase of the industrially produced organic pigment quinacridone was studied by 3D electron diffraction. The average crystal structure was obtained directly from the data and validated by energy minimization. A model describing the experimentally observed diffuse scattering was proposed.

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dl-Norleucine (2-aminohexanoic acid, C 6 H 13 NO 2 ) forms a double-layer structure in all known phases (, , ). The crystal structure of the -phase was redetermined at 173 K. Diffraction patterns of theand -phases frequently show diffuse streaks parallel to c*, which indicates a stacking disorder of the layers. A symmetry analysis was carried out to derive possible stacking sequences. Lattice-energy minimizations by force fields and by dispersioncorrected density functional theory (DFT-D) were performed on a set of ordered model structures with Z = 4, 8 and 16 with different stacking sequences. The calculated energies depend not only on the arrangement of neighbouring double layers, but also of next-neighbouring double layers. Stacking probabilities were calculated from the DFT-D energies. According to the calculated stacking probabilities large models containing 100 double layers were constructed. Their simulated diffraction patterns show sharp reflections for h + k = 2n and diffuse streaks parallel to c* through all reflections with h + k = 2n + 1. Experimental single-crystal X-ray diffraction revealed that at 173 K norleucine exists in the -phase with stacking disorder. After reheating to room temperature, the investigated crystal showed a diffraction pattern with strong diffuse scattering parallel to c* through all reflections with h + k = 2n + 1, which is in good agreement with the simulated disordered structure.

The crystal structures of 4-chloro-5-methyl-2-ammoniobenzenesulfonate and of the corresponding derivatives 4,5-dimethyl-and 4,5-dichloro-2-ammoniobenzenesulfonates have been determined from laboratory X-ray powder diffraction data. The tautomeric state of all three compounds could also be unequivocally determined from laboratory data, using careful Rietveld refinements. The tautomeric state was confirmed by IR spectroscopy. The compounds are neither isostructural to each other nor to the 5-chloro-4-methyl derivate, despite the similar size of the chloro and methyl substituents. The influence of the chloro and methyl substituents on the packing and on the thermal stability is demonstrated. All crystal structures were confirmed by dispersion-corrected DFT calculations. For the 4-chloro-5-methyl and the 4,5-dichloro derivatives the DFT calculations indicated that the observed polymorph should not be the thermodynamical one. However, no other polymorphs could be found in experimental polymorph screening, even using seeding with the corresponding isostructural phases. Obviously the DFT methods need further improvements.

Chloro(phthalocyaninato)aluminium [(CHN)AlCl, Pigment Blue 79] is a molecular compound which crystallizes in a layer structure with stacking disorder. Order-disorder theory was applied to analyse and explain the stacking disorder and to determine the symmetry operations, which generate subsequent layers from a given one. Corresponding ordered structural models were constructed and optimized by force field and dispersion-corrected density functional theory methods. The superposition of the four lowest-energy stackings lead to a structure in which every second double layer looks to be ordered; in the other double layers the molecules occupy one of two lateral positions. This calculated superposition structure agrees excellently with an (incomplete) experimental structure determined from single-crystal data. From the optimized ordered models, the stacking probabilities and the preferred local arrangements were derived. Packing effects such as the distortion of the molecules depending on the arrangement of neighbouring molecules could also be determined.