Wobbling and Hopping: Studying Dynamics of CO₂ Adsorbed in Metal–Organic Frameworks via ¹⁷O Solid-State NMR

Knowledge of adsorbed gas dynamics within microporous solids is crucial for the design of more efficient gas capture materials. We demonstrate that ¹⁷O solid-state NMR (SSNMR) experiments allow one to obtain accurate information on CO₂ dynamics within metal–organic frameworks (MOFs), using CPO-27-M (M = Mg, Zn) as examples. Variable-temperature (VT) ¹⁷O SSNMR spectra acquired from 150 to 403 K yield key parameters defining the CO₂ motions. VT ¹⁷O SSNMR spectra of CPO-27-Zn indicate relatively weaker metal–oxygen binding and increased CO₂ dynamics. ¹⁷O SSNMR is a sensitive probe of CO₂ dynamics due to the presence of both the quadrupolar and chemical shielding interactions, and holds potential for the investigation of motions within a variety of microporous materials.