(A) Raw in situ DRIFTS spectra of activated 3-4-3-Mg2(dobpdc) (grey curve), 3-4-3-Mg2(dobpdc) dosed with 400 mbar of 12CO2 and 13CO2 at 120°C (dark blue and yellow curves, respectively), and the isotopic difference spectrum (light blue curve). The 13CO2 spectrum was used as a baseline, isolating vibrations caused by inserted CO2. Vibrations corresponding to diagnostic carbamate bands are labeled. (B) Room-temperature 13C solid-state magic angle spinning NMR (16.4 T) of Mg2(dobpdc)(3-4-3) dosed with 1038 mbar of 13CO2. The resonance at 162.6 ppm was assigned as carbamate. (C) 1H⟶13C heteronuclear correlation (contact time 100 μs) spectrum and correlation assignments. (D) Predicted structures of Mg2(dobpdc)(3-4-3), Mg2(dobpdc)(3-4-3)(CO2), and Mg2(dobpdc)(3-4-3)(CO2)2 obtained from structural relaxations with vdW-corrected DFT. Green, grey, red, blue, and white spheres represent Mg, C, O, N, and H atoms, respectively.