Isostructurality, polymorphism and mechanical properties of some hexahalogenated benzenes:: The nature of halogen•••halogen interactions
Isostructurality, polymorphism and mechanical properties of some hexahalogenated benzenes:: The nature of halogen•••halogen interactions
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DOI：
10.1002/chem.200500983
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发表时间：
2006-03-01
影响因子：
4.3
通讯作者：
Desiraju, GR
中科院分区：
文献类型：
--
作者：
Reddy, CM;Kirchner, MT;Desiraju, GR
卤素原子之间的分子间相互作用的性质，X中心点X（X = Cl，Br，I），仍然是热门的兴趣，因为这些相互作用可以用作晶体工程中的设计元素。六卤代苯（C6Cl6-nBrn，C6Cl6-nIn，C6Br6-nIn）的晶体结构主要有两种堆积模式，分别为单斜空间群P2（1）/n和三斜空间群P（1）。前者与C6Cl6同构，更为常见。对于缺乏反转对称性的分子，采用这种单斜结构必然会导致晶体学无序。在C6Cl6中，平面分子形成Cl中心点Cl接触以及π中心点π堆叠相互作用。当C6Cl6晶体沿其针状长度沿着机械压缩时，即[010]，由于在堆叠方向上的较强相互作用，发生弯曲变形。进一步的压缩在晶体中以蛇形运动连续传播，类似于位错的运动。C_6Cl_6晶体的弯曲与Cl心-点-中心-点-Cl相互作用的弱有关，而与π心-点-中心-点-中心-点-π堆积相互作用的强有关。三斜堆积不太常见，仅限于具有对称（1，3，5-和2，4，6-）卤素取代模式的分子。这种堆积类型的特征在于特定的、偏振诱导的X中心点X相互作用，其导致三重对称的X-3光子，特别是当X = I时;这导致分层的伪六边形结构，其中连续的平面层是反转相关的并且堆叠，使得一层中的凸起以空间填充的方式适合于下一层的凹陷。在施加机械应力时，三斜晶体仅沿着变形平面剪切。这种剪切是由层之间的滑动引起的。这些化合物的孪晶结构证明了弱层间相互作用的非特异性。研究的化合物之一（1，3，5-三溴-2，4，6-三碘苯）是二晶型的，采用单斜和三斜结构，并提出了多态性的原因。总之，在六卤代苯中，X中心点X相互作用需要考虑化学和几何模型。单斜晶系中的X中心点X相互作用是非特异性的，而在三斜晶系中，一些X中心点X相互作用是各向异性的、化学特异性的和晶体结构定向的。
The nature of intermolecular interactions between halogen atoms, X center dot center dot center dot X (X=Cl, Br, I), continues to be of topical interest because these interactions may be used as design elements in crystal engineering. Hexahalogenated benzenes (C6Cl6-nBrn, C6Cl6-nIn, C6Br6-nIn) crystallise in two main packing modes, which take the monoclinic space group P2(1)/n and the triclinic space group P (1) over bar. The former, which is isostructural to C6Cl6, is more common. For molecules that lack inversion symmetry, adoption of this monoclinic structure would necessarily lead to crystallographic disorder. In C6Cl6, the planar molecules form Cl center dot center dot center dot Cl contacts and also pi center dot center dot center dot pi stacking interactions. When crystals Of C6Cl6 are compressed mechanically along their needle length, that is, [010], a bending deformation takes place, because of the stronger interactions in the stacking direction. Further compression propagates consecutively in a snakelike motion through the crystal, similar to what has been suggested for the motion of dislocations. The bending of C6Cl6 crystals is related to the weakness of the Cl center dot center dot center dot Cl interactions compared with the stronger pi center dot center dot center dot pi stacking interactions. The triclinic packing is less common and is restricted to molecules that have a symmetrical (1,3,5- and 2,4,6-) halogen substitution pattern. This packing type is characterised by specific, polarisation-induced X center dot center dot center dot X interactions that result in threefold-symmetrical X-3 synthons, especially when X=I; this leads to a layered pseudohexagonal structure in which successive planar layers are inversion related and stacked so that bumps in one layer fit into the hollows of the next in a space-filling manner. The triclinic crystals shear on application of a mechanical stress only along the plane of deformation. This shearing arises from the sliding of layers against one another. Nonspecificity of the weak interlayer interactions here is demonstrated by the structure of twinned crystals of these compounds. One of the compounds studied (1,3,5-tribromo-2,4,6-triiodobenzene) is dimorphic, adopting both the monoclinic and triclinic structures, and the reasons for polymorphism are suggested. To summarise, both chemical and geometrical models need to be considered for X center dot center dot center dot X interactions in hexahalogenated benzenes. The X center dot center dot center dot X interactions in the monoclinic group are nonspecific, whereas in the triclinic group some X center dot center dot center dot X interactions are anisotropic, chemically specific and crystal-structure directing.