Fine-Tuning Pore Size by Shifting Coordination Sites of Ligands and Surface Polarization of Metal–Organic Frameworks To Sharply Enhance the Selectivity for CO2

Based upon the (3,6)-connected metal–organic framework {Cu­(L1)·2H2O·1.5DMF}∞ (L1 = 5-(pyridin-4-yl)­isophthalic acid) (SYSU, for Sun Yat-Sen University), iso-reticular {Cu­(L2)·DMF}∞ (L2 = 5-(pyridin-3-yl)­isophthalic acid) (NJU-Bai7; NJU-Bai for Nanjing University Bai group) and {Cu­(L3)·DMF·H2O}∞ (L3 = 5-(pyrimidin-5-yl)­isophthalic acid) (NJU-Bai8) were designed by shifting the coordination sites of ligands to fine-tune pore size and polarizing the inner surface with uncoordinated nitrogen atoms, respectively, with almost no changes in surface area or porosity. Compared with those of the prototype SYSU, both the adsorption enthalpy and selectivity of CO2 for NJU-Bai7 and NJU-Bai8 have been greatly enhanced, which makes NJU-Bai7 and NJU-Bai8 good candidates for postcombustion CO2 capture. Notably, the CO2 adsorption enthalpy of NJU-Bai7 is the highest reported so far among the MOFs without any polarizing functional groups or open metal sites. Meanwhile, NJU-Bai8 exhibits high uptake of CO2 and good CO2/CH4 selectivity at high pressure, which are quite valuable characteristics in the purification of natural gases.本数据集基于(3,6)-连接型金属有机框架（metal–organic framework, MOF）{Cu(L1)·2H₂O·1.5DMF}∞（其中L1为5-(吡啶-4-基)间苯二甲酸，SYSU即Sun Yat-Sen University，中山大学的缩写），通过调控配体的配位位点以微调孔径，并利用未配位氮原子极化孔道内表面，设计得到两款同构网状框架：{Cu(L2)·DMF}∞（L2为5-(吡啶-3-基)间苯二甲酸，对应材料编号NJU-Bai7；NJU-Bai为南京大学白课题组的缩写）与{Cu(L3)·DMF·H₂O}∞（L3为5-(嘧啶-5-基)间苯二甲酸，对应材料编号NJU-Bai8）。上述三款框架的比表面积与孔隙率几乎无差异。相较于原型框架SYSU，NJU-Bai7与NJU-Bai8的二氧化碳吸附焓及CO₂选择性均得到显著提升，使其成为燃烧后CO₂捕集的优良候选材料。值得注意的是，在未引入任何极化官能团或开放金属位点的MOF材料中，NJU-Bai7的CO₂吸附焓为目前已报道的最高值。与此同时，NJU-Bai8在高压条件下展现出优异的CO₂吸附容量与良好的CO₂/CH₄选择性，该特性在天然气净化工艺中具备重要应用价值。