Neutron diffraction structural study of CO₂ binding in mixed-metal CPM-200 metal-organic frameworks

Metal-organic frameworks featuring open metal coordination sites have been widely studied for the separation of gas mixtures. For CO₂/N₂ separations, these materials have shown considerable promise. Herein, we report the characterization of a subset of the well-known PCN-250 class of frameworks upon CO₂ adsorption via powder neutron diffraction methods. Noteably, in contrast to previously reported data, they display only moderate CO₂ adsorption enthalpies, based on metal cation-CO₂ interactions. Further, we show charge balance in these materials is likely achieved via ligand vacancies rather than the presence of micro₃-OH groups in the trimetallic cluster that comprises them.