Solid-state structures of rosette and crinkled tape motifs derived from the cyanuric acid melamine lattice
Solid-state structures of rosette and crinkled tape motifs derived from the cyanuric acid melamine lattice
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DOI：
10.1021/ja00039a096
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发表时间：
1992-06
影响因子：
15
通讯作者：
Jonathan A. Zerkowski;C. Seto;G. Whitesides
中科院分区：
文献类型：
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作者：
Jonathan A. Zerkowski;C. Seto;G. Whitesides
图1.基于1-2的重复单元的结构示意图。三聚氰胺由实心三角形表示，二乙基巴比妥酸由空心三角形表示，氢键三重组由三条连接的虚线表示。不利的空间相互作用的区域由箭头指示。7的结构将一对R基团叠加在2的单元上，以显示空间应变。乙醇作为溶剂化物。8图2（下）显示了Ib（X= C（CH 3）3）和2.9晶体中所有roxyl的平均平面是平行的：也就是说，它们不采用人字形堆积基序。晶格中不含结晶溶剂，我们假设X基团之间的非键空间相互作用和晶体中高堆积系数10的趋势之间的竞争对于确定1和2的1：1共晶采用哪种结构基序很重要。我们假定任何结构都必须保持氢键的三联体模式。对于小的基团X（F、Cl、Br、I、CH 3）的数量，观察到线性带3。当X变得大于CF 3或I时，相邻三聚氰胺上X基团之间的11个不利的横向非键合相互作用（图1）在走向褶皱结构4时被解除，但被与2的乙基的不利相互作用所取代（图2，底部）。12 The
Figure 1. Schematic representation of structures basedon repeating units of 1-2. Melamines are represented by filled triangles, diethylbarbituric acid is represented by open triangles, and the triad of hydrogen bonds is represented by the three connecting dotted lines. Regions of unfavorable steric interactions are indicated by the arrows. The structure of 7 superimposes one pair of R groups on a unit of 2 to showthe steric strain. ethanol as a solvate. 8 Figure 2 (lower) shows the structure of lb (X= C (CH3) 3) and 2.9 The mean planes of all the rosettes in the crystal are parallel: that is, they do not adopt a herringbone packing motif. No solvent of crystallization is included in the lattice.We hypothesize that a competition between nonbonded steric interactions between the X groups and a tendency for a high packing coefficient10 in the crystal is important in determining which structural motif is adopted by a 1: 1 cocrystal of 1 and 2. We assume that any structure must retain the triad pattern of hydrogen bonds. The linear tape 3 is observed for a number of groups X that are small (F, Cl, Br, I, CH3). When X becomes larger than CF3 or I, 11 unfavorable lateral nonbonding interactions between X groups on adjacent melamines (Figure 1) are relieved in going to the crinkled structure 4, but are replaced by unfavorable interactions with the ethyl groups of 2 (Figure 2, bottom). 12 The