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On the stacking disorder of dl ‐norleucine
Author(s) -
Czech Christian,
Glinnemann Jürgen,
Johansson Kristoffer E.,
Bolte Michael,
Schmidt Martin U.
Publication year - 2017
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520617012057
Subject(s) - stacking , crystallography , diffraction , chemistry , crystal structure , norleucine , x ray crystallography , density functional theory , crystal (programming language) , molecular physics , computational chemistry , physics , optics , biochemistry , programming language , organic chemistry , amino acid , methionine , computer science
dl ‐Norleucine (2‐aminohexanoic acid, C 6 H 13 NO 2 ) forms a double‐layer structure in all known phases (α, β, γ). The crystal structure of the β‐phase was redetermined at 173 K. Diffraction patterns of the α‐ and β‐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 dispersion‐corrected 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 = 2 n and diffuse streaks parallel to c * through all reflections with h + k = 2 n + 1. Experimental single‐crystal X‐ray diffraction revealed that at 173 K norleucine exists in the β‐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 = 2 n + 1, which is in good agreement with the simulated disordered structure.