title: Structure determination of forms I and II of phenobarbital from X-ray powder diffraction.
abstract: From pure powders of forms I and II of phenobarbital, X-ray diffraction patterns were recorded at room temperature. The starting crystal structural models were found by a Monte-Carlo simulated annealing method. The structures of the two forms were obtained through Rietveld refinements. Soft restraints were applied on bond lengths and bond angles, all H-atom positions were calculated. The cell of form I is monoclinic with the space group P2(1)/n, Z=12, Z'=3. Form II has a triclinic cell, with the space group P1 , Z=6, Z'=3. For both forms, the crystal cohesion is achieved by networks of N-H...O hydrogen bonds along [101]. The broadening of the Bragg peak profiles is interpreted in terms of isotropic strain effects and anisotropic size effects.
authors.affiliation: Laboratoire de Dynamique et Structure des Matériaux Moléculaires (UMR CNRS 8024), UFR de Physique, Bâtiment P5, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq CEDEX, France.
authors.forename: Cyril
authors.initials: C
authors.lastname: Platteau
authors.forename: Jacques
authors.initials: J
authors.lastname: Lefebvre
authors.forename: Stephanie
authors.initials: S
authors.lastname: Hemon
authors.forename: Carsten
authors.initials: C
authors.lastname: Baehtz
authors.forename: Florence
authors.initials: F
authors.lastname: Danede
authors.forename: Dominique
authors.initials: D
authors.lastname: Prevost
mesh_terms: D007536:Isomerism; D008958:Models, Molecular; D015394:Molecular Structure; D010634:Phenobarbital / Q000737:chemistry*; D033362:Powder Diffraction; D014961:X-Ray Diffraction
chemical_list: D010634:Phenobarbital