title: X-ray powder diffraction structure determination of gamma-butyrolactone at 180 K: phase-problem solution from the lattice energy minimization with two independent molecules.
abstract: The crystal structure of the solid phase of the dipolar aprotic solvent gamma-butyrolactone (BL1), C(4)H(6)O(2), has been solved using the atom-atom potential method and Rietveld-refined against powder diffraction data collected at T = 180 K with a curved position-sensitive detector (INEL CPS120) using Debye-Scherrer diffraction geometry with monochromatic X-rays. It was first deduced from the X-ray experiment that the lattice parameters are a = 10.1282 (4), b = 10.2303 (5), c = 8.3133 (4) A, beta = 93.291 (2) degrees and that the space group is P2(1)/a, with Z = 8 and two independent molecules in the asymmetric unit. The structure was then solved by global energy minimization of the crystal-lattice atom-atom potentials. The subsequent GSAS-based Rietveld refinement converged to the final crystal-structure model indicator R(F(2)) = 0.0684, profile factors R(p) = 0.0517 and R(wp) = 0.0694, and a reduced chi(2) = 1.671. After further cycles of heating and cooling, a powder diffraction pattern markedly different from the first pattern was obtained, again at T = 180 K, which we tentatively assign to a second polymorph (BL2). All the observed diffraction peaks are well indexed by a triclinic unit cell essentially featuring a doubling of the a axis. An excellent Le Bail fit is obtained, for which R(p) = 0.0312 and R(wp) = 0.0511.
authors.affiliation: Laboratoire Léon Brillouin, CEA Saclay, F-91191 Gif-sur-Yvette CEDEX, France.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Papoular
authors.forename: Hassan
authors.initials: H
authors.lastname: Allouchi
authors.forename: Alexandre
authors.initials: A
authors.lastname: Chagnes
authors.forename: A
authors.initials: A
authors.lastname: Dzyabchenko
authors.forename: Bernard
authors.initials: B
authors.lastname: Carré
authors.forename: Daniel
authors.initials: D
authors.lastname: Lemordant
authors.forename: Viatcheslav
authors.initials: V
authors.lastname: Agafonov
mesh_terms: D015107:4-Butyrolactone / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D033362:Powder Diffraction; D013696:Temperature; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D015107:4-Butyrolactone