Open AccessConcomitant polymorphism and a temperature‐dependent phase change in ( E )‐[1‐(4‐methoxyphenyl)‐3‐phenyl‐2‐propenylideneamino]oxyacetic acid
Author(s) -
Low John N.,
Skakle Janet M. S.,
Wardell James L.,
Glidewell Christopher
Publication year - 2005
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
eISSN - 1600-5740
pISSN - 0108-7681
DOI - 10.1107/s0108768105007421
Subject(s) - polymorphism (computer science) , concomitant , chemistry , medicinal chemistry , stereochemistry , materials science , medicine , genotype , biochemistry , gene
The title compound, C 18 H 17 NO 4 , crystallizes from ethanol at ambient temperature as two concomitant polymorphs (I) and (II), both monoclinic P 2 1 / c with Z ′ = 1. The less abundant form (I) undergoes a reversible phase‐transition at ca 173 K to a third monoclinic polymorph (III), P 2 1 / 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—H⋯O 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—H⋯N and C—H⋯π(arene) hydrogen bonds; in polymorph (III) the dimers are linked into chains by a C—H⋯π(arene) hydrogen bond. The interconversion of polymorphs (I) and (III) is a simple displacive phase transition.