title: Concomitant polymorphism and a temperature-dependent phase change in (E)-[1-(4-methoxyphenyl)-3-phenyl-2-propenylideneamino]oxyacetic acid.
abstract: The title compound, C(18)H(17)NO(4), crystallizes from ethanol at ambient temperature as two concomitant polymorphs (I) and (II), both monoclinic P2(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), P2(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...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.
authors.affiliation: Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland.
authors.forename: Janet M S
authors.initials: JM
authors.lastname: Skakle
authors.forename: John N
authors.initials: JN
authors.lastname: Low
authors.forename: James L
authors.initials: JL
authors.lastname: Wardell
authors.forename: Christopher
authors.initials: C
authors.lastname: Glidewell
mesh_terms: D000085:Acetates / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D010091:Oximes / Q000737:chemistry*; D013696:Temperature
chemical_list: C504134:(1-(4-methoxyphenyl)-3-phenyl-2-propenylideneamino)oxyacetic acid; D000085:Acetates; D010091:Oximes