title: Ab initio structure determination of phase II of racemic ibuprofen by X-ray powder diffraction.
abstract: Annealing of the quenched ibuprofen at 258 K yielded a new crystalline form, called phase II. Powder X-ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position-sensitive detector CPS120. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with rigid-body constraints for the phenyl group and soft restraints on the other interatomic bond lengths and bond angles. The cell volume is 5% larger than that of the conventional phase I at 258 K. It is also shown that the orientation of the propanoic acid group is drastically changed with respect to phase I, leading to strong modifications of the orientation of the O-H...O hydrogen bonds with respect to the chains of dimers. These structural considerations could explain the metastable character of this phase II.
authors.affiliation: Unité Matériaux et Transformations (UMR CNRS 8207), Université Lille 1, Sciences et Technologies, 59655 Villeneuve d'Ascq CEDEX, France. patrick.derollez@univ-lille1.fr
authors.forename: Patrick
authors.initials: P
authors.lastname: Derollez
authors.forename: Emeline
authors.initials: E
authors.lastname: Dudognon
authors.forename: Frédéric
authors.initials: F
authors.lastname: Affouard
authors.forename: Florence
authors.initials: F
authors.lastname: Danède
authors.forename: Natália T
authors.initials: NT
authors.lastname: Correia
authors.forename: Marc
authors.initials: M
authors.lastname: Descamps
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007052:Ibuprofen / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D011208:Powders / Q000737:chemistry*; D013237:Stereoisomerism; D014961:X-Ray Diffraction
chemical_list: D011208:Powders; D007052:Ibuprofen