Electron and Electrostatic Properties of Three Crystal Forms of Piracetam

The electron densities in three crystal forms of piracetam (triclinic form II, monoclinic form III, and triclinic piracetam monohydrate) were derived from high resolution X-ray diffraction experiments carried out at 100 K. For comparison, quantum mechanics calculations were also performed for the th...

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Bibliographic Details
Published in:Crystal growth & design 2011-06, Vol.11 (6), p.2528-2539
Main Authors: Chambrier, Marie-Hélène, Bouhmaida, Nouzha, Bonhomme, François, Lebègue, Sébastien, Gillet, Jean-Michel, Jelsch, Christian, Ghermani, Nour Eddine
Format: Article
Language:English
Subjects:
Condensed matter: structure, mechanical and thermal properties
Engineering Sciences
Exact sciences and technology
Materials
Physics
Structure of solids and liquids
crystallography
Structure of specific crystalline solids
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Summary:The electron densities in three crystal forms of piracetam (triclinic form II, monoclinic form III, and triclinic piracetam monohydrate) were derived from high resolution X-ray diffraction experiments carried out at 100 K. For comparison, quantum mechanics calculations were also performed for the three compounds. The experimental electron density was refined using the Hansen–Coppens multipole model. The electron deformation density and the electrostatic potential were carefully analyzed in the three forms of piracetam. The atomic charges obtained by the flux of the electric field were found in excellent agreement with those obtained by the conventional volume integration method. The charge values compare qualitatively well with those obtained by theoretical calculations. The total electrostatic force exerted on each atom of the molecule has been investigated by using the Maxwell stress tensor as well as the interatomic forces. The experimental electrostatic interaction energies between dimers in the three crystal forms of piracetam were also estimated. Monoclinic form III exhibits the strongest piracetam–piracetam dimer electrostatic interaction energy (−131.9 kJ/mol) compared to −116.0 and −103.3 kJ/mol found in triclinic form II and the monohydrate form, respectively. The experimental interaction electrostatic energy of the piracetam–water contact was estimated as −175.0 kJ/mol in the monohydrate form.
ISSN:1528-7483
1528-7505
DOI:10.1021/cg200291t