Acta Crystallographica Section B

Structural Science

Volume 61, Part 3 (June 2005)

research papers

Acta Cryst. (2005). B61, 312-320 [ doi:10.1107/S0108768105005392 ]

X-ray powder diffraction structure determination of -butyrolactone at 180 K: phase-problem solution from the lattice energy minimization with two independent molecules

R. J. Papoular, H. Allouchi, A. Chagnes, A. Dzyabchenko, B. Carré, D. Lemordant and V. Agafonov

Abstract: The crystal structure of the solid phase of the dipolar aprotic solvent [gamma] -butyrolactone (BL1), C₄H₆O₂, 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) Å, [beta] = 93.291 (2)° and that the space group is P2₁/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_F² = 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.

Keywords: butyrolactone; X-ray powder diffraction; atom-atom potential; low temperature; polymorphism.


	Text file (31.7 kbytes) BL1 data at T = 180 K

	Text file (31.7 kbytes) BL2 data at T = 180 K

	Text file (34.7 kbytes) BL1 Fullprof data

	Text file (34.7 kbytes) BL2 Fullprof data

	Portable Document Format (PDF) file (78.2 kbytes) XRD Spectum

	Portable Document Format (PDF) file (52.6 kbytes) XRD spectra

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