Acta Crystallographica Section B

Structural Science

Volume 61, Part 3 (June 2005)

research papers

Acta Cryst. (2005). B61, 321-328 [ doi:10.1107/S0108768105007421 ]

Concomitant polymorphism and a temperature-dependent phase change in (E)-[1-(4-methoxyphenyl)-3-phenyl-2-propenylideneamino]oxyacetic acid

J. M. S. Skakle, J. N. Low, J. L. Wardell and C. Glidewell

Abstract: The title compound, C₁₈H₁₇NO₄, crystallizes from ethanol at ambient temperature as two concomitant polymorphs (I) and (II), both monoclinic P2₁/c with Z' = 1. The less abundant form (I) undergoes a reversible phase-transition at ca 173 K to a third monoclinic polymorph (III), P2₁/n, with Z' = 2, while the more abundant polymorph (II) is unchanged down to 120 K. In each polymorph of (I)-(III) the molecules are linked by pairs of O-HO hydrogen bonds into cyclic dimers which are crystallographically centrosymmetric in (I) and (II), and approximately, but not crystallographically, centrosymmetric in (III). There are no direction-specific interactions between the hydrogen-bonded dimers in polymorph (I); in polymorph (II) the dimers are linked into sheets by C-HN and C-H [pi] (arene) hydrogen bonds; in polymorph (III) the dimers are linked into chains by a C-H [pi] (arene) hydrogen bond. The interconversion of polymorphs (I) and (III) is a simple displacive phase transition.

Keywords: polymorphism; phase change; hydrogen bonding; cyclic dimers.


	Structure factor file (CIF format) (186.6 kbytes) Contains datablock I

	Structure factor file (CIF format) (180.9 kbytes) Contains datablock s827

	Structure factor file (CIF format) (188.1 kbytes) Contains datablock js404

	Structure factor file (CIF format) (356.8 kbytes) Contains datablock s391

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