Rotationally disordered phase of 1,3-dibromo-5-iodo-2,4,6-trimethylbenzene at 293 K.
Rotationally disordered phase of 1,3-dibromo-5-iodo-2,4,6-trimethylbenzene at 293 K.
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1,3-二溴-5-碘-2,4,6-三甲基苯在 293 K 时的旋转无序相。
DOI：
10.1107/s0108270109032715
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
J. Meinnel
中科院分区：
文献类型：
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作者：
S. Ghanemi;O. Hernandez;A. Boudjada;J. Meinnel
在室温下的晶体状态下，二溴代三甲基苯（1，3-二溴-5-碘-2，4，6-三甲基苯）分子C9 H9 Br 2 I易于发生强烈的无序，显然只涉及三个卤素位点（分别被66.7%的Br和33.3%的I占据）。根据先前公布的NMR测量，这种无序的旋转类型，对应于整个分子在三个可辨别的位置之间的快速2 pi/3随机面内重新取向。由于标题化合物的C2 v理想化分子对称性，这种旋转无序可以首次通过衍射法揭示，尽管它在室温下在类似晶体堆积但具有D3 h分子对称性的其他三卤代均三甲苯中被间接怀疑。面对Br/I位点和甲基的平均内环角分别为124.14（6）和115.85（2）度。芳环的法线与（100）面的法线之间的角度为4.1度。TLS分析表明，只有芳香环和甲基作为一个刚体的热振动。
In the crystal state at room temperature, the molecule of dibromoiodomesitylene (1,3-dibromo-5-iodo-2,4,6-trimethylbenzene), C9H9Br2I, is prone to strong disorder, apparently involving only the three halogen sites (occupied identically by 66.7% Br and 33.3% I). This disorder, of the rotational type according to previously published NMR measurements, corresponds to fast 2pi/3 stochastic in-plane reorientations of the whole molecule between three discernable locations. This kind of rotational disorder can be revealed for the first time by diffractometry thanks to the C2v idealized molecular symmetry of the title compound, although it has been indirectly suspected at room temperature in other trihalogenomesitylenes of similar crystal packing but of D3h molecular symmetry. The average endocyclic angles facing the Br/I sites and the methyl groups are 124.14 (6) and 115.85 (2) degrees, respectively. The angle between the normal to the aromatic ring and the normal to the (100) plane is 4.1 degrees. TLS analysis indicates that only the aromatic ring and the methyl groups behave as a rigid body with respect to the thermal librations.