Properties and Detailed Adsorption of CO₂ by M₂(dobpdc) with N,N-Dimethylethylenediamine Functionalization

We have systematically investigated the CO₂ adsorption performance and microscopic mechanism of N,N-dimethylethylenediamine (mm-2) appended M₂(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 M₂(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.