Rapid Cs + Capture via Multiple Supramolecular Interactions in Anionic Metal-Organic Framework Isomers.

Metal-organic frameworks (MOFs) provide an ideal platform for ion exchange due to their high porosity and structural designability; however, developing MOFs that have the essential characteristics for ion exchange remains a challenge. These crucial features include fast kinetics, selectivity, and stability. We present two anionic isomers, DGIST-2 (2D) and DGIST-3 (3D), comprising distinctly arranged 5-(1,8-naphthalimido)isophthalate ligands and In 3+ cations. Interestingly, in protic solvents, DGIST-2 transforms into a hydrolytically stable crystalline phase, DGIST-2'. DGIST-2' and DGIST-3 exhibit rapid Cs + adsorption kinetics, as well as high Cs + affinity in the presence of competing cations. The mechanism for rapid and selective sorption is explored based on the results of single-crystal X-ray diffraction analysis of Cs + -incorporated DGIST-3. In Cs + -containing solutions, the loosely incorporated dimethylammonium countercation of the anionic framework is replaced by Cs + , which is held in the hydrophobic cavity by supramolecular ion-ion and cation-π interactions.