Physisorbed CO 2 at 68 ppm is readily assigned from previous literature. Both the carbonyl, 175-178 ppm, and hydroxyl, 90-110 ppm, environments are assigned initially in comparison to the predicted shifts for bicarbonate clusters in Fig. . Finally, the peak at -50 to -70 ppm is assigned to unreacted Zn-hydroxide site, in agreement with literature. The clear identification of carbonyl and hydroxyl functional groups (at an approximate 2:1 ratio, see S12) is in agreement with the accepted bicarbonate binding structure in MFU-4l and gives promise to O NMR as a technique for making speciation assignments.