We, for the first time, systematically investigated the crystal structures, adsorption properties, and microscopic mechanism of CO 2 capture with ethylenediamine (en)-appended isostructural M 2 (dobpdc) materials (M = Mg, Sc-Zn), using spin polarized density functional theory (DFT) calculations. The binding energies of en range from 142 to 210 kJ/mol. The weakest binding materials are en-Cr 2 (dobpdc) and en-Cu 2 (dobpdc). Two typical models, the pair model and the chain model, have been considered for CO 2 adsorption. Generally, the chain model is more stable than the pair model. The CO 2 adsorption energies of the chain model are in the range of 30-96 kJ/mol, with a strong metal dependence. Among these, the en-Sc 2 (dobpdc) and en-Cu 2 (dobpdc) have the highest and lowest CO 2 adsorption energies, respectively. Moreover, the dynamic progress of CO 2 adsorption has been unveiled via exploration of the full reaction pathway, including transition states and intermediates. First, the CO 2 molecule interacts with en-MOFs to form a physisorbed complex with a shallow potential well. This is followed by overcoming a relatively large energy barrier to form a chemisorbed complex. Finally, ammonium carbamate is formed along the one-dimensional channels within the pore with a small energy barrier for configuration transformation. These results agree well with the experimental observations. Understanding the detailed microscopic mechanism of CO 2 capture is quite crucial for improving our fundamental knowledge base and potential future applications. This work will improve our understanding of CO 2 adsorption with amine functionalized MOFs. We expect our results to stimulate future experimental and theoretical research and advance the development of this field.