We demonstrate this combined computational and O NMR approach on the well-studied MFU-4l MOF. The established metal-binding mechanism (eq. 1) in MFU-4l is refined to provide precise insights into the dynamics of the bound bicarbonate species. Then, through application to KHCO 3 and K 2 CO 3 •1.5 H 2 O solid powders and using additional MLFF molecular dynamics, we are able to elucidate an improved, mixed bicarbonate-carbonate (eq. 2/3) capture mechanism for KHCO 3 -CD-MOF using 17 O NMR spectroscopy.