A new polymorph (form II) is reported for the 1:1 dimethyl sulfoxide solvate of 2,3,5,6-tetrafluoro-1,4-diiodobenzene (TFDIB·DMSO or C6F4I2·C2H6SO). The structure is similar to that of a previously reported polymorph (form I) [Britton (2003). Acta Cryst. E59, o1332-o1333], containing layers of TFDIB molecules with DMSO molecules between, accepting I...O halogen bonds from two TFDIB molecules. Re-examination of form I over the temperature range 300-120 K shows that it undergoes a phase transformation around 220 K, where the DMSO molecules undergo re-orientation and become ordered. The unit cell expands by ca 0.5 Å along the c axis and contracts by ca 1.0 Å along the a axis, and the space-group symmetry is reduced from Pnma to P212121. Refinement of form I against data collected at 220 K captures the (average) structure of the crystal prior to the phase transformation, with the DMSO molecules showing four distinct disorder components, corresponding to an overlay of the 297 and 120 K structures. Assessment of the intermolecular interaction energies using the PIXEL method indicates that the various orientations of the DMSO molecules have very similar total interaction energies with the molecules of the TFDIB framework. The phase transformation is driven by interactions between DMSO molecules, whereby re-orientation at lower temperature yields significantly closer and more stabilizing interactions between neighbouring DMSO molecules, which lock in an ordered arrangement along the shortened a axis.

中文翻译：

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2,3,5,6-四氟-1,4-二碘苯的二甲基亚砜溶剂化物的多态性和相变。

据报道，一种新的多晶型物（形式II）是2,3,5,6-四氟-1,4-二碘苯的1：1二甲基亚砜溶剂化物（TFDIB·DMSO或C6F4I2·C2H6SO）。其结构类似于先前报道的多晶型物（形式I）[Britton（2003）。Acta Cryst。[E59，o1332-o1333]，包含TFDIB分子层与之间的DMSO分子层，接受来自两个TFDIB分子的I ... O卤素键。在300-120 K的温度范围内对晶型I的重新检查表明，它在220 K附近经历了相变，其中DMSO分子经历了重新定向并变得有序。晶胞沿c轴扩展约0.5Å，沿a轴收缩约1.0Å，并且空间群的对称性从Pnma降低到P212121。根据220 K收集的数据对晶型I进行细化，可以捕获相变之前晶体的（平均）结构，其中DMSO分子显示出四个不同的无序成分，分别对应于297 K和120 K结构的重叠。使用PIXEL方法评估分子间相互作用能表明，DMSO分子的各种取向与TFDIB构架的分子具有非常相似的总相互作用能。相变是由DMSO分子之间的相互作用驱动的，从而在较低的温度下重新取向会在相邻DMSO分子之间产生更紧密和更稳定的相互作用，从而沿缩短的轴锁定有序排列。对应于297和120 K结构的叠加层。使用PIXEL方法评估分子间相互作用能表明，DMSO分子的各种取向与TFDIB构架的分子具有非常相似的总相互作用能。相变是由DMSO分子之间的相互作用驱动的，从而在较低的温度下重新取向会在相邻DMSO分子之间产生更紧密和更稳定的相互作用，从而沿缩短的轴锁定有序排列。对应于297和120 K结构的叠加层。使用PIXEL方法评估分子间相互作用能表明，DMSO分子的各种取向与TFDIB构架的分子具有非常相似的总相互作用能。相变是由DMSO分子之间的相互作用驱动的，从而在较低的温度下重新取向会在相邻DMSO分子之间产生更紧密和更稳定的相互作用，从而沿缩短的轴锁定有序排列。