Unveiling Unexpected Modulator-CO2 Dynamics within a Zirconium Metal-Organic Framework

Carboncapture, storage, and utilization (CCSU) represents an opportunityto mitigate carbon emissions that drive global anthropogenic climatechange. Promising materials for CCSU through gas adsorption have beendeveloped by leveraging the porosity, stability, and tunability ofextended crystalline coordination polymers called metal-organicframeworks (MOFs). While the development of these frameworks has yieldedhighly effective CO2 sorbents, an in-depth understandingof the properties of MOF pores that lead to the most efficient uptakeduring sorption would benefit the rational design of more efficientCCSU materials. Though previous investigations of gas-poreinteractions often assumed that the internal pore environment wasstatic, discovery of more dynamic behavior represents an opportunityfor precise sorbent engineering. Herein, we report a multifaceted in situ analysis following the adsorption of CO2 in MOF-808 variants with different capping agents (formate, acetate,and trifluoroacetate: FA, AA, and TFA, respectively). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)analysis paired with multivariate analysis tools and in situ powder X-ray diffraction revealed unexpected CO2 interactionsat the node associated with dynamic behavior of node-capping modulatorsin the pores of MOF-808, which had previously been assumed to be static.MOF-808-TFA displays two binding modes, resulting in higher bindingaffinity for CO2. Computational analyses further supportthese dynamic observations. The beneficial role of these structuraldynamics could play an essential role in building a deeper understandingof CO2 binding in MOFs.