Environmentally Responsive Threading, Dethreading, and Fixation of Anion-Induced Pseudorotaxanes

The tetracationic macrocycle cyclo[2](2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene) hexafluorophosphate (14+·4PF6−) acts as a large, flexible “molecular box” that supports the formation of environmentally responsive anion-induced pseudorotaxanes, as well as other extended structures, including metal-linked supramolecular polyrotaxanes. Specifically, the combination of the tetracation 14+ and bis-carboxylate guests derived from 4,4′-biphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid results in the formation of pseudorotaxanes that respond to changes in environmental stimuli, including pH and temperature. The resulting structures can be “locked into place” via the addition of a metal-linker in the form of Ag(I); this gives rise to an ordered metal-linked polyrotaxane. The interpenetrated constructs described in this article were characterized in solution and in the solid state by one- and two-dimensional (1H and NOESY) NMR spectroscopy, as well as by mass spectrometry (ESI-MS) and single-crystal X-ray diffraction methods.

四阳离子大环化合物环己[2](2,6-二(1H-咪唑-1-基)吡啶)[2](1,4-亚二甲苯)六氟磷酸盐（1⁴⁺·4PF₆⁻）可作为一种大尺寸、兼具柔性的"分子盒"，能够介导环境响应型阴离子诱导假轮烷及其他扩展结构的形成，其中包括金属连接型超分子聚轮烷。具体而言，四阳离子主体1⁴⁺与源自4,4'-联苯二甲酸和2,6-萘二甲酸的双羧酸客体相结合时，可生成可响应pH、温度等环境刺激的假轮烷结构。通过加入Ag(I)形式的金属连接剂，可将上述所得结构"锁定"于对应位置，进而得到有序的金属连接型聚轮烷。本文所报道的互穿型组装体，已通过溶液及固态下的一维、二维（¹H及NOESY）核磁共振波谱法、电喷雾电离质谱（ESI-MS）以及单晶X射线衍射法完成了完整表征。