Skakle Janet M S, Low John N, Wardell James L, Glidewell Christopher
Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland.
Acta Crystallogr B. 2005 Jun;61(Pt 3):321-8. doi: 10.1107/S0108768105007421. Epub 2005 May 13.
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.
标题化合物C(18)H(17)NO(4)在室温下从乙醇中结晶为两种伴随的多晶型物（I）和（II），均为单斜晶系P2(1)/c，Z' = 1。含量较少的晶型（I）在约173 K时经历可逆相变，转变为第三种单斜多晶型物（III），P2(1)/n，Z' = 2，而含量较多的多晶型物（II）在降至120 K时保持不变。在（I） - （III）的每种多晶型物中，分子通过O - H...O氢键对连接成环状二聚体，在（I）和（II）中这些二聚体具有晶体学中心对称性，在（III）中近似但不具有晶体学中心对称性。在多晶型物（I）中，氢键连接的二聚体之间不存在方向特异性相互作用；在多晶型物（II）中，二聚体通过C - H...N和C - H...π(芳烃)氢键连接成片；在多晶型物（III）中，二聚体通过C - H...π(芳烃)氢键连接成链。多晶型物（I）和（III）之间的相互转化是一种简单的位移相变。
