Motivated by the computational results, experimental O NMR spectra were acquired for a series of representative adsorbents. First, a control experiment for activated Mg 2 (dobpdc), i.e., with no amine functionalisation, revealed a relatively sharp resonance for physisorbed CO 2 at 61.5 ppm (Figure ). (Ee-2)-Mg 2 (dobpdc)-CO 2 (ee-2 = N,Ndiethylethylenediamine) was then selected as the first amine functionalised sample, as previous characterisation has confidently assigned this material to form ammonium carbamate chains. Excitingly, the O MAS NMR spectrum supports ammonium carbamate chain formation, with two oxygen environments of similar signal intensity observed (Figure ). Deconvolution of these two resonances, aided by a multiple-quantum MAS (MQMAS) spectrum (Figure ), gave δ iso , C Q and η Q values in good agreement with DFT-calculated parameters for ammonium carbamate chains (Table ). The agreement for six NMR parameters gives much greater confidence in the structural assignment than previous NMR work. It is important to note that the calculated DFT structures exclude the presence of water when considering the adsorption mechanism. Care has been taken to exclude water from the system experimentally. The spectrum for (ee-2)-Mg 2 (dobpdc) presented two additional peaks, one at 70.5 ppm assigned to physisorbed CO 2 and a smaller second peak at around -22 ppm. The identity of this minor peak is unknown, though it potentially arises from CO 2 reacting with defects in the metal-organic framework, since this signal was also weakly observed in the spectrum of unfunctionalized Mg 2 (dobpdc). Finally, the O NMR spectrum could be acquired rapidly, with an acquisition time of ~27 minutes, and with an estimated cost of O enriched CO 2 gas of £50 per sample, which could be reduced in future by optimising the gas dosing line used to prepare samples. Although care has been taken to ensure adequate delays during the acquisition of these experiments, the integrated signal intensities cannot be considered truly quantitative owing to the differences in T 1 and T 2 relaxation and the different nutation rates for O nuclei with different quadrupolar couplings.