First, the lowest shift peak at δ iso = 163 ppm is assigned as a 'dynamic hydroxyl' environment due to very good agreement to both the experimental and MLFF-MD simulated values for KHCO 3 (s) (Table ). Both the δ iso and C Q values agree well, and η Q discrepancies are explained through broad lineshapes giving poorly defined line shape features for fitting. Additionally, both DFS and MQMAS experiments qualitatively support this assignment of a dynamic environment with limited NMR signal enhancement at the corresponding shift region seen in the DFS spectrum (Fig. ) and MQMAS signal being particularly challenging to obtain for the same lower shift region (Fig. ). The two higher shift peaks at δ iso = 181, 192 ppm are more challenging to assign precisely, although both clearly fall in the carbonyl region from comparison to both calculated (Table ) and experimental and literature results (Table ). From 13 C NMR (Fig. ), two carbon species are expected -at a ratio of ≈ 1 : 1.6 (Fig. ). Thus, the three oxygen environments assigned must correspond to two (bi)carbonate species of the same ratio. From the multi-field data (Fig. ), the ratio of the 181 ppm peak to the combined total of the 163 and 192 ppm peaks remains constant at around 1:1.8-1.9. Given the broadness of the 17 O NMR peaks, these ratios are in reasonable agreement with the 13 C NMR. Thus, the 163 and 192 ppm O peaks can be tentatively assigned as belonging with the 159 ppm C peak as bicarbonate 'dynamic hydroxyl' and carbonyl environments, respectively. The 181 ppm O peak can thus be assigned with the higher shift C environment at 163 ppm as a carbonyl of a carbonate species. This is supported by the generally lower O δ iso values calculated for carbonate carbonyls compared to in bicarbonate (Fig. , Table ) -as well as generally higher C NMR shifts for carbonates (see Table ). The final piece of validation for the assignments in Fig. comes from MD simulations using the MACE-MP-0 pre-trained ML force-field. Recently introduced, MACE-MP-0 is widely applicable to a large variety of materials, in particular MOFs, without the need for additional and, in this case, expensive DFT training. Molecular dynamic simulations reveal the existence of extensive hydrogen bond network surrounding the active sites (see Fig. ). We investigate the plausibility of proton hops between hydroxyl, carbonyl, hydroxide and framework alcohol sites by assessing the thermodynamic stability of various hydrogen networks. We find that a carbonyl-hydroxyl proton transfer can be facilitated by a proton hop along the hydrogen network (Figs. and), providing a plausible mechanism for a dynamic hydroxyl group within the bicarbonate.