Charge‐density analysis and electrostatic properties of 2‐carboxy‐4‐methylanilinium chloride monohydrate obtained using a multipolar and a spherical‐charges model
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.
Document Type: Research Article
Publication date: July 1, 2012