Acta Cryst. (2005). B61, 96-102 [ doi:10.1107/S0108768104031738 ]
Abstract: A temperature-controlled X-ray powder diffraction experiment, complemented with TGA and DSC analysis, allowed us to follow changes in the molecular conformation and hydrogen-bond patterns of 4-piperidinecarboxylic acid. The presence of three phases is confirmed. Phase 1 represents the monohydrated form of 4-piperidinecarboxylic acid, which exists from room temperature to 359 K, where dehydration occurs. Phase 2 measured at 363 K corresponds to an anhydrous form of the acid. At ca 458 K the onset of a second, more gradual transition is observed, which ends at around 543 K. Phase 3 measured at 543 K is a high-temperature anhydrous form of the acid. The structures of phases 2 and 3 were solved from synchrotron powder diffraction data by simulated annealing using the DASH program and refined by the Rietveld method. The phase changes are accompanied by modification of the hydrogen-bond patterns and of the torsional orientation of the terminal carboxylate group. This group makes a 49° rotation about the C1-C2 bond during the first transition.
Keywords: Temperature-controlled powder diffraction; hydrogen bonds; Rietveld refinement.
 |   Structure factor file (CIF format) (68.3 kbytes) |
| Structure factor file (CIF format) (52.2 kbytes) |
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