Influence of fluorine side-group substitution on the crystal structure formation of benzene-1,3,5-trisamides
Influence of fluorine side-group substitution on the crystal structure formation of benzene-1,3,5-trisamides
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DOI：
10.1039/c4ce01077a
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发表时间：
2014-01-01
期刊：
影响因子：
3.1
通讯作者：
Senker, Juergen
中科院分区：
文献类型：
--
作者：
Zehe, Christoph;Schmidt, Marko;Senker, Juergen
通过粉末X射线衍射、多维和多核固态NMR光谱和量子化学计算的组合，我们能够确定1，3，5-三（2-氟-2-甲基丙酰氨基）苯的晶体结构。固态核磁共振实验通过预测不对称单元的含量和NH中心点中心点OC氢键网络的存在来指导结构解。除了实空间结构解和Rietveld精化之外，定量的基于（FF）的-F-19-F-19双量子再耦合实验提供了成本函数来确定甲基和氟原子的位置。这种特殊的氟取代的三酰胺的结构溶液说明了氟侧基取代对苯-1，3，5-三甲酰胺的常见柱状堆积基序的影响。同样在1，3，5-三（2，2-二甲基丙酰氨基）苯的情况下，超分子聚集然后通过在各个柱内形成三螺旋NH中心点中心点OC氢键网络来引导。相比之下，在每个侧链中一个甲基被氟原子取代导致二维NH中心点中心点OC氢键图案，导致层间仅具有货车范德华相互作用的层状晶体结构。由于氟不参与氢键网络，并且两种化学单元表现出相似的空间需求，因此填充的根本差异很可能是由分子极性的变化引起的。
By a combination of powder X-ray diffraction, multidimensional and multinuclear solid-state NMR spectroscopy and quantum chemical calculations, we were able to determine the crystal structure of 1,3,5-tris(2-fluoro-2-methylpropionylamino)benzene. Solid-state NMR experiments guided the structure solution by predicting the content of the asymmetric unit and the presence of a NH center dot center dot center dot OC hydrogen bond network. In addition to real-space structure solution and Rietveld refinement, quantitative symmetry-based (FF)-F-19-F-19 double-quantum recoupling experiments provided a cost function to determine the positions of the methyl groups and fluorine atoms. The structure solution of this particular fluorine-substituted trisamide illustrates the impact of fluorine side-group substitution on the common columnar packing motif of benzene-1,3,5-tricarboxamides. As also in the case 1,3,5-tris(2,2-dimethylpropionylamino)benzene, the supra-molecular aggregation is then guided by the formation of triple helical NH center dot center dot center dot OC hydrogen bond networks within the individual columns. In contrast, the substitution of one methyl group by a fluorine atom in each side chain results in a two-dimensional NH center dot center dot center dot OC hydrogen bond pattern, leading to a lamellar crystal structure with only van der Waals interactions between the layers. Since fluorine is not involved in the hydrogen bond network and both chemical units exhibit a similar steric demand, the fundamental differences of the packing are most probably caused by changes in the molecular polarity.