Acta Crystallographica Section A

Foundations of Crystallography

Volume 68, Part 4 (July 2012)

research papers

Acta Cryst. (2012). A68, 452-463 [ doi:10.1107/S0108767312016571 ]

Charge-density analysis and electrostatic properties of 2-carboxy-4-methylanilinium chloride monohydrate obtained using a multipolar and a spherical-charges model

N. Dadda, A. Nassour, B. Guillot, N. Benali-Cherif and C. Jelsch

Abstract: The new crystal structure of 2-carboxy-4-methylanilinium chloride monohydrate was determined by X-ray diffraction and refined using three different electron-density models. In the first model, the ELMAM2 multipolar electron-density database was transferred to the molecule. Theoretical structure factors were also computed from periodic density functional theory calculations and yielded, after multipolar-atoms refinement, the second charge-density model. An alternative electron-density modelling, based on spherical atoms and additional charges on the covalent bonds and electron lone-pair sites, was used in the third model in the refinement versus the theoretical data. The crystallographic refinements, structural properties, electron-density distributions and molecular electrostatic potentials obtained from the different charge-density models were compared. As the number of variables refined in the different models is the same, the R factor is a good indicator of refinement quality. The R factor is best for multipolar modelling, presumably because of the greater flexibility and larger number of parameters to model the electron density compared to the spherical-charges model. The electrostatic potentials around the molecule show a high correlation coefficient between the three models.

Keywords: atomic charges; bonding electron density; lone pairs.


	Chemical Markup Language (CML) file (6.4 kbytes) [ doi:10.1107/S0108767312016571/pc5010Isup4.cml ] Supplementary material

	Portable Document Format (PDF) file [ doi:10.1107/S0108767312016571/pc5010sup3.pdf ] Supplementary material

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