Design Strategy for the Controlled Generation of Cationic Frameworks and Ensuing Anion-Exchange Capabilities

Abstract

Cationic frameworks are an emerging class of exceptional solid adsorbents capable of encapsulating highly toxic and persistent anionic pollutants. The controlled generation of cationic frameworks, however, lags behind the abundant design strategies devised to control the structures and topologies of neutral frameworks. In this regard, we report a rational approach that allows the conversion of the synthetic approach toward constructing a neutral framework into one allowing for the synthesis of a cationic one without incurring any changes to the overall topology or the selected metal ion. We demonstrate that the replacement of a functional group on an organic linker that promotes a similar coordination mode, but bearing one less negative charge, can yield the systematic generation of cationic frameworks. Moreover, we confirm the cationic nature of the metal−organic frameworks through preliminary anion-exchange experiments and propose a method to retain permanent porosity in cationic frameworks through the use of strongly binding anions. Altogether, these results show great promise for the construction of tunable nanoporous frameworks capable of carrying out anion-exchange processes.

Concurrent Enhancement of Acetylene Uptake Capacity and Selectivity by Progressive Core Expansion and Extra‐Framework Anions in Pore‐Space‐Partitioned Metal–Organic Frameworks

“…We further studied the effects of different anions, as chemical properties and geometry of these anions dictate their spatial arrangement in the pacs system [16] . Prior to gas sorption studies, we confirmed phase purity of Co 3 ‐cpt‐tph‐x (x=Cl − , Br − , ClO 4 − , BF 4 − ) by comparing their powder X‐ray diffraction (PXRD) with simulated ones (Figure S4).…”

Using Postsynthetic X-Type Ligand Exchange to Enhance CO2 Adsorption in Metal–Organic Frameworks with Kuratowski-Type Building Units

“…There are numerous examples of postsynthetic exchange of charge-balancing anions residing within the pores of cationic MOFs. − However, inner-sphere, postsynthetic X-type ligand exchange (PXLE) at MOF metal nodes has been less studied, partly as a result of the relative paucity of materials containing exchangeable X-type ligands. Hupp and co-workers pioneered solvent-assisted ligand incorporation (SALI) as a means of immobilizing nonstructural carboxylate or phosphonate groups at linker-deficient 6- or 8-connected Zr 6 nodes (Figure a) .…”

Anion-Dependent Catalytic C–C Bond Cleavage of a Lignin Model within a Cationic Metal–Organic Framework

“…One common approach relies on the introduction of well-studied catalytically active guest species within the channels or cages of MOFs, enabling highly efficient reactions. , In this regard, positively or negatively charged MOFs have the advantage of allowing a straightforward and efficient inclusion of anionic or cationic metal complexes with well-defined catalytic behaviors through ion-metathesis reactions. The exchange of noncoordinating ions in MOFs has previously been shown to impact a number of physical properties, including gas adsorption behaviors and proton conductivity. − Thus far, however, tuning the catalytic performance of a charged MOF via replacement of nonactive ionic guest species has yet to be reported.…”