The 13 C NMR spectrum of (e-2)2-Mg2(dobpdc) (Figure , e-2 = N-ethylethylenediamine) shows two peaks at 162.1 and 124.7 ppm, corresponding to chemisorbed and physisorbed CO2, respectively. The chemisorbed CO2 signal is enhanced using a CP experiment and this signal is assigned to the formation of an ammonium carbamate chain upon CO2 adsorption. In contrast, the (dmpn)2-Zn2(dobpdc) shows two chemisorbed CO2 peaks with an intense signal at 161.2 ppm, assigned to carbamic acid pairs and a weaker signal at d = 164 ppm, assigned to a small quantity of ammonium carbamates (Figure ). It is clear that the number and type of environments in (e-2)2-Mg2(dobpdc) and (dmpn)2-Zn2(dobpdc) are different, a range of C chemical shift values are reported in the literature for ammonium carbamate chains and carbamic acids. The small differentiation in chemical shifts between the similar C environments in these mechanisms, therefore, means that the confidence in the assignments of these binding modes by C MAS NMR spectroscopy alone is low.