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Polymorphism of N , N ′′‐Diacetylbiuret Studied by Solid‐State 13 C and 15 N NMR Spectroscopy, DFT Calculations, and X‐ray Diffraction
Author(s) -
Macholl Sven,
Lentz Dieter,
Börner Frank,
Buntkowsky Gerd
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601843
Subject(s) - crystallography , nuclear magnetic resonance crystallography , chemistry , solid state nuclear magnetic resonance , nuclear magnetic resonance spectroscopy , chemical shift , nmr spectra database , crystallization , hydrogen bond , molecule , x ray crystallography , diffraction , intermolecular force , spectroscopy , carbon 13 nmr satellite , crystal structure , spectral line , fluorine 19 nmr , nuclear magnetic resonance , stereochemistry , physics , organic chemistry , quantum mechanics , astronomy , optics
The molecular configuration and crystal structure of solid polycrystalline N , N ′′‐diacetylbiuret (DAB), a potential nitrogen‐rich fertilizer, have been analyzed by a combination of solid‐ and liquid‐state NMR spectroscopy, X‐ray diffraction, and DFT calculations. Initially a pure NMR study (“NMR crystallography”) was performed as available single crystals of DAB were not suitable for X‐ray diffraction. Solid‐state 13 C NMR spectra revealed the unexpected existence of two polymorphic modifications (α‐ and β‐DAB) obtained from different chemical procedures. Several NMR techniques were applied for a thorough characterization of the molecular system, revealing chemical shift anisotropy (CSA) tensors of selected nuclei in the solid state, chemical shifts in the liquid state, and molecular dynamics in the solid state. Dynamic NMR spectroscopy of DAB in solution revealed exchange between two different configurations, which raised the question, is there a correlation between the two different configurations found in solution and the two polymorphic modifications found in the solid state? By using this knowledge, a new crystallization protocol was devised which led to the growth of single crystals suitable for X‐ray diffraction. The X‐ray data showed that the same symmetric configuration is present in both polymorphic modifications, but the packing patterns in the crystals are different. In both cases hydrogen bonds lead to the formation of planes of DAB molecules. Additional symmetry elements, a two‐fold screw in the case of α‐DAB and a c ‐glide plane in the case of β‐DAB, lead to a more symmetric (α‐DAB) or asymmetric (β‐DAB) intermolecular hydrogen‐bonding pattern for each molecule.