Naphthalene-Pillared Benzene Triimide Cage: An Efficient Receptor for Polyhedral Anions and a General Tool for Probing Theoretically-Existing Anion-π Binding Motifs

Abstract

A triangular prism cage 2 with benzene triimide (BTI) as the bases, 2,7-naphthalene dimethyl as the supporting pillars was designed and synthesized efficiently. The two parallel BTI planes constitute a cavity of 7.58 Å which allows inclusion of anions of various sizes. Cage 2 showed so far the strongest binding affinity to a series of polyhedral (tetrahedral and octahedral) anions including PF 6 -(24651 M -1 ), ClO 4 -(28234 M -1 ), CH 3 SO 3 -(30571 M -1 ), BF 4 -(31613 M -1 ) and HSO 4 -(84623 M -1 ). The obtained eleven crystal structures of 2⸧Xcomplexes with different anions demonstrated that multiple and cooperative anion- interactions contribute synergistically to the strong complexation. The series of complex structures systematically suggested that cage 2 is a good, general tool for probing anion- binding motifs that have only been predicted in theoretical calculations. For anions of triangular (NO 3 -) and polyhedral (BF 4 -, ClO 4 -, PF 6 -) shapes, the as-predicted most stable anion- binding motifs with charge-neutral  systems were experimentally observed for the first time.

Ion−π interactions for constructing organic luminescent materials

“…[24,29] Since anion−π interaction was unambiguously proved in the solid state in 2004, [32,61,62] they have received growing attention in supramolecular chemistry. [26,29,63] Anion−π interactions take vital parts in anion/molecular recognition, [64][65][66][67][68][69] ion/electron transporting, [37,[70][71][72] and anion−π catalyst [31,73,74] .…”

Anion‐π Interaction for Molecular Recognition of Anions: Focus on Cooperativity with Hydrogen Bonding

“…Recently, another example 136 was proposed where the benzene linker is replaced by a naphthalene linker. [161] This cage offers a huge cavity of ~7.6 Å (Reprinted with permission from [105] . Copyright (2019), American Chemical Society) (Reprinted with permission from [160] .…”

Synthesis of a Highly Electron-Deficient, Water-Stable, Large Ionic Box: Multielectron Accumulation and Proton Conductivity

“…Organic systems that can accumulate electrons and transport ions will be important for harvesting energy and mimicking biomolecules. , Macrocycles endowing electron-deficient π-scaffolds are superior hosts to anions and electrons compared to open structures. − Although electron-deficient π-scaffolds drive electron uptake, radical formation, and anion−π interactions, , proton transport along π-acidic scaffolds is highly challenging to realize in an aqueous medium. Thus, organization of water as a proton precursor , along electron-deficient π-scaffolds is yet to be synthetically realized.…”