Gelbrich Thomas, Braun Doris E, Ellern Arkady, Griesser Ulrich J
Institute of Pharmacy, University of Innsbruck , Innrain 52, 6020 Innsbruck, Austria.
Cryst Growth Des. 2013 Mar 6;13(3):1206-1217. doi: 10.1021/cg301639r. Epub 2013 Jan 28.
Four polymorphic forms of methyl paraben (methyl 4-hydroxybenzoate, ), denoted (melting point 126 °C), (109 °C), - (107 °C), and - (112 °C), have been investigated by thermomicroscopy, infrared spectroscopy, and X-ray crystallography. The crystal structures of the metastable forms , -, and - have been determined. All polymorphs contain the same O-H···O=C connected catemer motif, but the geometry of the resulting H-bonded chain is different in each form. The ' = 3 structure of (stable form; space group ) contains local symmetry elements. The crystal packing of each of the four known crystal structures of was compared with the crystal structures of 12 chemical analogues. Close two-dimensional relationships exist between - and a form of methyl 4-aminobenzoate and between - and dimethyl terephthalate. The lattice energies of the four methyl paraben structures have been calculated with a range of methods based on ab initio electronic calculations on either the crystal or single molecule. This shows that the differences in the induction energy of the different hydrogen-bonded chain geometries have a significant effect on relative lattice energies, but that conformational energy, repulsion, dispersion, and electrostatic also contribute.
对尼泊金甲酯（4-羟基苯甲酸甲酯）的四种多晶型物，分别记为α（熔点126℃）、β（109℃）、γ-（107℃）和δ-（112℃），通过热显微镜、红外光谱和X射线晶体学进行了研究。已确定了亚稳晶型β、γ-和δ-的晶体结构。所有多晶型物都包含相同的O-H···O=C连接的链状二聚体基序，但每种晶型中形成的氢键链的几何形状不同。α（稳定晶型；空间群）的Z = 3结构包含局部对称元素。将尼泊金甲酯四种已知晶体结构中的每一种的晶体堆积与12种化学类似物的晶体结构进行了比较。在β-与一种4-氨基苯甲酸甲酯晶型之间以及γ-与对苯二甲酸二甲酯之间存在紧密的二维关系。已使用一系列基于对晶体或单分子进行从头算电子计算的方法计算了四种尼泊金甲酯结构的晶格能。这表明不同氢键链几何形状的诱导能差异对相对晶格能有显著影响，但构象能、排斥能、色散能和静电能也有贡献。
