CO 2 uptake measurements were carried out using a thermogravimetric analyser (Q500, TA Instruments). Samples (10-20 mg) were pre-treated in flowing nitrogen at 120 °C for 2 h, to remove residual impurities. After cooling the samples to 25 °C, the purge gas was switched to 15% CO 2 in N 2 . After 1 h, the temperature was raised to 50, then 75 °C. The CO2 uptake at each temperature was calculated based on the corresponding weight gain. The samples were then heated to 700 °C under N 2 gas, before switching to air for 30 min to remove any residual carbon deposit. Amine content was determined based on the weight loss during decomposition. However, it is clear by fitting the 1D O MAS spectra (Figure , Figure ) that an additional signal at lower chemical shifts is needed to fully deconvolute the lineshape for these materials. Although, a fourth signal is not observed in the MQMAS spectrum, likely owing to the low efficiency of multiple quantum excitation for nuclei with large quadrupolar couplings, this signal can be clearly resolved in the O MAS spectrum at 20.0 T and 23.5 T (Figure , SI Figure , Figure , SI Figure ). In all cases, peaks from physisorbed CO 2 are not observed in the MQMAS spectra as these species are likely to have negligible quadrupolar couplings. Table . The experimental and DFT calculated NMR parameters for CO 2 dosed (e-2)-Mg 2 (dobpdc). In addition to the DFT structure shown in the main text (Figure , Table ), two alternative structures were investigated. The carbamic acid structure is the structure resulting from geometry optimisation of the structure Figure . The second structure is the same structure as in Figure , i.e., without geometry optimisation. This second structure had the same hydrogen bonding arrangement as CO 2 dosed (ee-2)-Mg 2 (dobpdc) (Figure ) and show a better fit between DFT calculated and experimental parameters.