Charge-Separated and Lewis Paired Metal-Organic Framework for Anion Exchange and CO Chemical Fixation.

Charge-separated metal-organic frameworks (MOFs) are a unique class of MOFs that can possess added properties originating from the exposed ionic species. A new charge-separated MOF, namely, UNM-6 synthesized from a tetrahedral borate ligand and Co cation is reported herein. UNM-6 crystalizes into the highly symmetric P43n space group with fourfold interpenetration, despite the stoichiometric imbalance between the B and Co atoms, which also leads to loosely bound NO anions within the crystal structure. These NO ions can be quantitatively exchanged with various other anions, leading to Lewis acid (Co ) and Lewis base (anions) pairs within the pores and potentially cooperative catalytic activities. For example, UNM-6-Br, the MOF after anion exchange with Br anions, displays high catalytic activity and stability in reactions of CO chemical fixation into cyclic carbonates.