Ortho-Substituent Effects on Diphenylurea Packing Motifs,Crystal Growth & Design

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Ortho-Substituent Effects on Diphenylurea Packing Motifs
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2017-08-31 00:00:00 , DOI: 10.1021/acs.cgd.7b00757
Marina A. Solomos ₁ , Taylor A. Watts ₁ , Jennifer A. Swift ₁

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Hydrogen bonding between urea groups is a widely used motif in crystal engineering and supramolecular chemistry studies. In an effort to discern how the steric and electronic properties of substituents affect the molecular conformation and crystal packing of ortho-substituted N,N′-diphenylureas (oPUs), herein we report the synthesis, characterization, and polymorph screening of eight members of this family. Of the 16 total oPU structures known (including nine structures from this study and seven previously reported), only two are isostructural. These 16 structures are sorted into three general architecture types based on their hydrogen bond topologies. In Type I, urea molecules related by translation form linear one-dimensional (1D) hydrogen bonded chains. In Type II, urea molecules rotate about a 1D hydrogen bond axis forming twisted chains. Urea groups do not hydrogen bond to one another in Type III. Energy calculations performed at the B3LYP/6-31G(d,p) level show a higher rotational barrier about the amide bond in oPUs compared to meta-substituted diphenylureas (mPUs), which may explain the smaller range of torsion angles observed in oPUs compared to mPUs. Although ortho-substitution does not seem to limit the hydrogen bonding between urea groups in most cases, a notably higher percentage of oPU phases are polar compared to PUs with other substitution patterns. This suggests restricted conformations might offer some advantage in achieving acentric materials.

中文翻译：

邻位取代基对二苯脲包装图案的影响

脲基团之间的氢键是在晶体工程和超分子化学研究中广泛使用的基序。为了弄清取代基的空间和电子性质如何影响邻位取代的N，N'-二苯基脲（o PU）的分子构象和晶体堆积，我们在此报告8个分子的合成，表征和多晶型物筛选这个家庭。16总的öPU结构是已知的（包括本研究中的9种结构和先前报道的7种结构），只有2种是同构结构。基于它们的氢键拓扑结构，这16种结构可分为三种常规结构类型。在类型I中，通过翻译关联的尿素分子形成线性一维（1D）氢键链。在II型中，尿素分子绕一维氢键轴旋转，形成扭曲链。尿素基团在III型中不会彼此氢键键合。在B3LYP / 6-31G（d，p）处进行的能量计算显示，与间取代的二苯基脲（m PU）相比，o PU中酰胺键周围的旋转势垒更高，这可以解释在扭转角中观察到的较小扭转角范围。o PU与m脓。尽管在大多数情况下邻位取代似乎并不限制尿素基团之间的氢键，但与具有其他取代方式的聚氨酯相比，邻位聚氨酯相的比例明显更高。这表明受限制的构象可能在获得非中心材料方面提供一些优势。

更新日期：2017-08-31

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