Acta Crystallographica Section B

Structural Science

Volume 59, Part 3 (June 2003)

research papers

Acta Cryst. (2003). B59, 404-415 [ doi:10.1107/S0108768103005792 ]

Mechanism of the first-order phase transition of an acylurea derivative: observation of intermediate stages of transformation with a detailed temperature-resolved single-crystal diffraction method

D. Hashizume, N. Miki, T. Yamazaki, Y. Aoyagi, T. Arisato, H. Uchiyama, T. Endo, M. Yasui and F. Iwasaki

Abstract: The process of the first-order solid-to-solid phase transition of 1-ethyl-3-(4-methylpentanoyl)urea (1) was observed by means of a detailed temperature-resolved single-crystal diffraction method, which resembles watching a series of stop-motion photographs. The transition consists of two elementary processes, one supramolecular and the other molecular. Crystal structures from before and after the phase transition are isostructural. The straight-ribbon-like one-dimensional hydrogen-bonding structure is formed and stacked to form a molecular layer. The geometry of the layer is retained during the phase transition. The relative position of the layer with its neighbours, on the other hand, changes gradually with increasing temperature. The change is accelerated at the temperature representing the start of the endotherm seen in the DSC curves of (1). The structural variation yields void space between the neighbouring layers. When the void space grows enough that the crystal is unstable, the 3-methylbutyl group on the last of the molecules turns into a disordered structure with drastic conformational changes to fill up the void space. The phase transition process is well supported with simple force-field calculations. A crystal of 1-(4-methylpentanoyl)-3-propylurea (2), which shows no solid-to-solid phase transitions, was also analysed by the same method for comparison.

Keywords: phase transition; temperature-resolved measurement; dynamics in organic crystal.


	Structure factor file (CIF format) (102.1 kbytes) Contains datablock ethyl98K

	Structure factor file (CIF format) (112.6 kbytes) Contains datablock ethyl298K

	Structure factor file (CIF format) (106.6 kbytes) Contains datablock ethyl328K

	Structure factor file (CIF format) (95.4 kbytes) Contains datablock ethyl348K

	Structure factor file (CIF format) (104.1 kbytes) Contains datablock ethyl350K

	Structure factor file (CIF format) (96.8 kbytes) Contains datablock ethyl352K

	Structure factor file (CIF format) (104.3 kbytes) Contains datablock ethyl354K

	Structure factor file (CIF format) (84.4 kbytes) Contains datablock ethyl356K

	Structure factor file (CIF format) (117.8 kbytes) Contains datablock ethyl358K

	Structure factor file (CIF format) (117.4 kbytes) Contains datablock ethyl360K

	Structure factor file (CIF format) (116.0 kbytes) Contains datablock ethyl362K

	Structure factor file (CIF format) (122.9 kbytes) Contains datablock ethyl364K

	Structure factor file (CIF format) (117.1 kbytes) Contains datablock ethyl366K

	Structure factor file (CIF format) (112.2 kbytes) Contains datablock ethyl368K

	Structure factor file (CIF format) (111.2 kbytes) Contains datablock ethyl370K

	Structure factor file (CIF format) (113.6 kbytes) Contains datablock ethyl372K

	Structure factor file (CIF format) (96.5 kbytes) Contains datablock ethyl374K

	Structure factor file (CIF format) (106.3 kbytes) Contains datablock propyl98K

	Structure factor file (CIF format) (122.1 kbytes) Contains datablock propyl298K

	Structure factor file (CIF format) (77.7 kbytes) Contains datablock propyl348K

Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.