A Molecular Insight into the Dehydration of a Metal-Organic Framework and its Impact on the CO₂ Capture

Metal-organic frameworks (MOFs) are porous material formed by the self-assembly of metallic ligands and organic linkers. They are a good candidate for CO₂ gas capture because they have large surface areas and the metal or linker can be tuned to improve CO₂ uptake. In the quest for water and acid stable MOFs, a phosphonate-based organic linker has recently been designed by Glavinovic et al. (Chem. Eur. J. 2022, 28, e202200874). By combining ionic calcium nodes, water and methanol molecules, they formed a microporous network, CALF-37. This network has been shown to be robust and can maintain its pore shape even in absence of water molecules or by the inclusion of gas molecules, such as CO₂ . The network can be heated to release the water and methanol molecules and form a dehydrated MOF, which retains its shape with the imprinted pore within. Herein, we perform molecular dynamics (MD) simulations in order to provide insight into the CO₂ capture and sequestration ability of the CALF-37. We model the dehydration of the inactivated MOF (HCALF-37) in the absence and in the presence of methanol molecules by progressively withdrawing water molecules from the MOF networks. We determine the crystal structure of the intermediate states from HCALF-37 to CALF-37 and shed light on the critical role of water molecules in the mediation of metal-linker bonds. Our calculations also reveal that the favorable interactions between the CO₂ molecules and the aromatic core of the linkers and metallic ions are responsible for the efficient sequestration of the gas in the CALF-37.