Ionic metal-organic frameworks (iMOFs): Design principles and applications

Metal-organic frameworks (MOFs) have commanded significant attention in recent years on account of the applicability of these materials across several disciplines in material chemistry. The liberty of tuning the coordination nanospaces owing to the infinite choice of organic linkers and multivariate oxidation states of the metal nodes bestows a distinguished advantage of designable architectures to this class of materials. Majority of the reported MOFs comprise of neutral frameworks as the net positive charge on the metal ions is satisfied by the negative charge of anionic ligands or the coordinated anions of the metal salt used in synthesis. Although being non-trivial, the synthesis of ionic MOFs (iMOFs) affords several distinct advantages over the routine neutral frameworks by virtue of the isolated charged species in confined nanospaces. The development and potential applications of such cationic or anionic frameworks has been discussed thoroughly in this review. The design principles governing the formation of such charge-polarized MOFs have been outlined through representative examples. The state-of-the-art ion exchange performances of competing materials have been compared and a future perspective of such ionic-MOFs is proposed.