Macrocycle-Directed Construction of Tetrahedral Anion-π Receptors for Nesting Anions with Complementary Geometry.

Manipulation of the emerging anion-π interactions in a highly cooperative manner through sophisticated host design represents a very challenging task. In this work, unprecedented tetrahedral anion-π receptors have been successfully constructed for complementary accommodation of tetrahedral and relevant anions. The synthesis was achieved by a macrocycle-directed approach by using large macrocycle precursors bearing four reactive sites, which enabled a kinetic-favored pathway and afforded the otherwise inaccessible tetrahedral cages in considerable yields. Crystal structure suggested that the tetrahedral cages have an enclosed three-dimensional cavity surrounded by four electron-deficient triazine faces in a tetrahedral array. The complementary accommodation of a series of tetrahedral and relevant anions including BF4 - , ClO4 - , H2 PO4 - , HSO4 - , SO4 2- and PF6 - was revealed by ESI-MS and DFT calculations. Crystal structures of ClO4 - and PF6 - complexes showed that the anion was nicely encapsulated within the tetrahedral cavity with up to quadruple cooperative anion-π interactions by an excellent shape and size match. The strong anion-π binding was further confirmed by negative ion photoelectron spectroscopy measurements.