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A variable-temperature X-ray diffraction and theoretical study of conformational polymorphism in a complex organic molecule (DTC)

机译：复合有机分子（DTC）中的可变温度X射线衍射与构象多态性的理论研究

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摘要

Two conformational crystal polymorphs of 3-diethylamino-4-(4-methoxyphenyl)-1,1-dioxo-4H-1 lambda(6),2-thiazete-4-carbonitrile (DTC) have been analyzed in the 100 K-room temperature range by single crystal X-ray diffraction and high quality DFT calculations. DTC has strongly polar as well as aliphatic substituents but no hydrogen bonding groups, and thus qualifies as a test molecule for the relative importance of electrostatic vs. dispersion-repulsion terms. The two polymorphs have the same P2(1)/n space group and differ by a flipping of the -OCH3 group, the two conformations being almost equi-energetic and separated by a low barrier. The system is monotropic in the observed temperature range with nearly identical thermal expansion coefficients and energy-temperature slopes, one phase consistently predicted to be more stable in agreement with the relative ease of appearance. Energy decompositions show that the electrostatic term is dominant and stabilizes with decreasing temperature. Dispersion and repulsion show the expected behavior, the former becoming more stabilizing at lower temperature in contrast with increasing repulsion at higher density. Absolute values and trends are very similar in the two phases, explaining the small total energy difference. Geometrical analyses of intermolecular contacts using fingerprint plots, as well as the study of molecular dipole moments as a function of T in the framework of the Quantum Theory of Atoms in Molecules, reveal more details of phase stability.
机译：在100 k室中分析了3-二乙基氨基-4-（4-甲氧基苯基）-1,1-二氧基苯基-4H-1λ（6），2-噻嗪酮-4-1-1λ（DTC）的两个构象晶体多晶型物。温度范围由单晶X射线衍射和高质量DFT计算。 DTC具有强极性和脂族取代基，但没有氢键组，因此有资格作为静电与分散术语的相对重要性的测试分子。两种多晶型物具有相同的P2（1）/ N空间组，并且通过翻转-Och3组的翻转而不同，两个构象几乎是高能的，并且由低屏障分开。该系统在观察到的温度范围内单调，具有几乎相同的热膨胀系数和能量温度斜率，一相始终预测与相对易于外观的一致性更稳定。能量分解表明，静电术语是显性的，稳定在降低温度下。分散和排斥呈现预期的行为，前者在较低温度下变得更稳定，与较高密度的排斥增加。两个阶段的绝对值和趋势非常相似，解释了较小的总能量差。使用指纹图的分子间触点的几何分析，以及分子原子量子原子骨架框架中的分子偶极矩的研究，揭示了相位稳定性的更多细节。

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  • 来源
    《RSC Advances》 |2018年第67期|共10页
  • 作者

    Gionda Andrea; Macetti Giovanni; Loconte Laura; Rizzato Silvia; Orlando Ahmed M.; Gatti Carlo; Lo Presti Leonardo;

  • 作者单位

    Univ Milan Dept Chem Via Golgi 19 I-20133 Milan Italy;

    Univ Milan Dept Chem Via Golgi 19 I-20133 Milan Italy;

    Univ Milan Dept Chem Via Golgi 19 I-20133 Milan Italy;

    Univ Milan Dept Chem Via Golgi 19 I-20133 Milan Italy;

    Univ Milan Dept Chem Via Golgi 19 I-20133 Milan Italy;

    Aarhus Univ Ctr Mat Crystallog Langelandsgade 140 DK-8000 Aarhus C Denmark;

    Univ Milan Dept Chem Via Golgi 19 I-20133 Milan Italy;

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