Anion-Afforded Functions of Ionic Metal–Organic Frameworks: Ionochromism, Anion Conduction, and Catalysis

Abstract

The exchangeable counterions in ionic metal–organic frameworks (IMOFs) provide facile and versatile handles to manipulate functions associated with the ionic guests themselves and host–guest interactions. However, anion-exchangeable stable IMOFs combining multiple anion-related functions are still undeveloped. In this work, a novel porous IMOF featuring unique self-penetration was constructed from an electron-deficient tris­(pyridinium)-tricarboxylate zwitterionic ligand. The water-stable IMOF undergoes reversible and single-crystal-to-single-crystal anion exchange and shows selective and discriminative ionochromic behaviors toward electron-rich anions owing to donor–acceptor interactions. The IMOFs with different anions are good ionic conductors with low activation energy, the highest conductivity being observed with chloride. Furthermore, integrating Lewis acidic sites and nucleophilic guest anions in solid state, the IMOFs act as heterogeneous and recyclable catalysts to efficiently catalyze the cycloaddition of CO2 to epoxides without needing the use of halide cocatalysts. The catalytic activity is strongly dependent upon the guest anions, and the iodide shows the highest activity. The results demonstrate the great potential of developing IMOFs with various functions related to the guest ions included in the porous matrices.

A Review of Stimuli-Responsive Smart Materials for Wearable Technology in Healthcare: Retrospective, Perspective, and Prospective

“…These materials exhibit a reversible color change from the original color to a new one. When the stimulus is withdrawn (i.e., the ion inducing the ionochromic response is removed), the compound returns to its original color [ 142 , 143 ]. The ionochromic process can occur based on different mechanisms, including the following [ 137 ]: halochromism owing to a change in acidic or alkaline pH; acidochromism stimulated by acid; metallochromism deriving from the formation of colored complexes from metal ions and chelating ligands.…”

Bifunctional metal–organic frameworks afforded by postsynthetic modification for efficient cycloaddition of CO2 and epoxides

“…This can offer an opportunity to investigate the anion effects on CCE, which was rarely reported in the literature. [ 52,60 ] As a result, the 1‐Eu‐MeI catalyst displayed the highest catalytic performance for the synthesis of cyclic carbonate. To the best of our knowledge, 1‐Eu ‐MeX (X = Cl − , Br − , and I − ) is the first Eu‐based ionic MOF obtained by postsynthetic N ‐methylation for CCE.…”

A layered Mn-based coordination polymer as an efficient heterogeneous catalyst for CO2 cycloaddition under mild conditions

“…Thus, the development of efficient, stable, and recycled heterogeneous catalysts to achieve the cycloaddition of CO 2 with epoxides is very urgent. [10][11][12] Coordination polymers (CPs) and metal-organic frameworks (MOFs) are emerging as fascinating crystalline materials assembled from metal ions and organic linkers. [13][14][15][16][17] Due to their porosity, tunable architecture, homogeneous active sites, and excellent stability, CPs or MOFs have been identified as promising heterogeneous catalysts for various reactions including the cycloaddition of CO 2 and epoxides.…”

“…Thus, the development of efficient, stable, and recycled heterogeneous catalysts to achieve the cycloaddition of CO 2 with epoxides is very urgent. 10–12…”