Ligand-Assisted Enhancement of CO₂ Capture in Metal–Organic Frameworks

Using density functional theory with a van der Waals-corrected functional, we elucidate how CO2 binds to a novel “BTT-type” metal–organic framework (MOF) featuring open metal centers. We show that CO2 binds most favorably to open metal cation sites, but with an adsorption energy that can be three times more sensitive to the choice of the bridging ligand than to metal cation choice. A strong, three-site interaction between CO2 and the open-metal site is predicted, with the binding energy enhanced by up to a factor of 2, depending on the ligand. The CO2-MOF binding can be attributed to a combination of electrostatics and vdW dispersive interactions, both of which are critically sensitive to the local environment, and both of which contribute nearly equally to the overall binding strength. We show that a judicious choice of the organic linker and the metal center allows the binding energy to be tuned from 34.8 kJ/mol (for CaBTTri) to a maximum of 64.5 kJ/mol (MgBTT).我们采用结合范德华校正泛函（van der Waals-corrected functional）的密度泛函理论（density functional theory），阐明了二氧化碳（CO₂）与一类带有开放金属位点的新型“BTT型”金属有机框架（metal–organic framework, MOF）的结合机制。研究发现，CO₂最优选的结合位点为开放金属阳离子位点，但其吸附能对桥联配体选择的敏感性是对金属阳离子选择的三倍。我们预测CO₂与开放金属位点间存在显著的三位点相互作用，结合能可因配体差异最高提升至原水平的2倍。CO₂与MOF的结合可归因于静电作用与范德华色散相互作用的协同效应，二者均对局部环境极为敏感，且对整体结合强度的贡献近乎均等。通过合理选择有机连接体与金属中心，可将结合能从CaBTTri的34.8 kJ/mol调控至MgBTT的最大值64.5 kJ/mol。