Design and self-assembly of wide and robust coordination cages

The self-assembly of a new class of coordination cages formed from two tetrapyridyl-substituted cavitands connected through four square-planar palladium or platinum complexes is reported. The shape of the internal cavity resembles an ellipsoid with a calculated volume of 840 Å(3). The four lateral portals have a diameter of about 6 Å, large enough to allow the fast entrance/egress of counterions in solution. The platinum cages 3a,e cannot be disassembled using triethylamine as competitive ligand and they are kinetically stable at room temperature, whereas the palladium cages 3b-d, 3f-h are disassembled and kinetically labile under the same conditions. The different solubility properties of the cage components have allowed the extension of this self-assembly protocol to the liquid–liquid interface.

本文报道了一类新型配位笼 (coordination cages) 的自组装过程：该类配位笼由两个四吡啶取代的穴状配体 (tetrapyridyl-substituted cavitands) 通过四个平面正方形构型的钯或铂配合物 (square-planar palladium or platinum complexes) 连接构筑而成。其内部空腔呈椭球形 (ellipsoid)，计算得到的体积为840 ų。四个侧向窗口的直径约为6 Å，足以允许溶液中的反离子 (counterions) 快速进出。铂基配位笼3a、e无法以三乙胺 (triethylamine) 作为竞争性配体 (competitive ligand) 实现解离，在室温下表现出动力学稳定性；而钯基配位笼3b~d、3f~h在相同条件下则可发生解离，呈现动力学易解离 (kinetically labile) 特性。得益于笼状组分间不同的溶解性能，该自组装方案 (self-assembly protocol) 可被拓展至液-液界面 (liquid–liquid interface) 体系中。