We have systematically investigated the CO2 adsorption performance and microscopic mechanism of N,N-dimethylethylenediamine (mm-2) appended M-2 (dobpdc) (dobpdc(4-) = 4,4' -dioxidobiphenyl-3,3'-dicarboxylate; M = Mg, Sc-Zn) with density functional theory. These calculations show that the mm-2 has strong interactions with the open metal site of these structures via the first amine, and the mm-2 binding energies are generally between 123 and 172 kJ/mol. After the CO2 is attached, the ammonium carbamate molecule is created by insertion. The CO2 adsorption energies (31-81 kJ/mol) depend on the metal used (Mg; Sc-Zn). The microscopic mechanism of the CO2 adsorption process is presented at the atomic level, and the detailed potential energy surface and reaction path information are provided. The CO2 molecule and mm-2 grafted M-2(dobpdc) are firstly combined via physical interactions, and then, the complex is converted into an N-coordinated zwitterion intermediate over a large energy barrier (1.02-1.51 eV). Finally, the structure is rearranged into a stable ammonium carbamate configuration through a small energy barrier (0.05-0.25 eV). We hope that this research will contribute to the understanding and production of real-world carbon capture materials.