Charge-Separated and Lewis Paired Metal-Organic Framework for Anion Exchange and CO2 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. We report a new charge-separated MOF, namely UNM-6, synthesized from a tetrahedral borate ligand and Co 2+ cation. UNM-6 crystalizes into the highly symmetric P-43n space group with four-fold interpenetration, despite the stoichiometric imbalance between the B and Co atoms, which also leads to loosely bound NO 3 - anions within the crystal structure. These NO 3 - ions can be quantitatively exchanged with various other anions, leading to Lewis acid (Co 2+ ) 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 2 chemical fixation into cyclic carbonates.