Flexible metal–organic frameworks (MOFs) can show exceptional selectivity and capacity for adsorption of CO₂. The incorporation of CO₂ into flexible MOFs that have Cu²⁺ coordination centers and organic pillar ligands is accompanied by a distortion of the framework lattice arising from chemical interactions between these components and CO₂ molecules. CO₂ adsorption yields a reproducible lattice expansion that is enabled by the rotation of the pillar ligands. The structures of Cu₂(pzdc)₂(bpy) and Cu₂(pzdc)₂(bpe), CPL-2 and CPL-5, were evaluated using in situ synchrotron X-ray powder diffraction at room temperature at CO₂ gas pressures up to 50 atm. The structural parameters exhibit hysteresis between pressurization and depressurization. The pore volume within CPL-2 and CPL-5 increases at elevated CO₂ pressure due to a combination of the pillar ligand rotation and the overall expansion of the lattice. Volumetric CO₂ adsorption measurements up to 50 atm reveal adsorption behavior consistent with the structural results, including a rapid uptake of CO₂ at low pressure, saturation above 20 atm, and hysteresis evident as a retention of CO₂ during depressurization. A significantly greater CO₂ uptake is observed in CPL-5 in comparison with predictions based on CO₂ pressure-induced expansion of the pore volume available for adsorption, indicating that the flexibility of the CPL structures is a key factor in enhancing adsorption capacity.

中文翻译：

---

柔性铜联吡啶金属-有机骨架中CO2吸附过程中的晶格膨胀和配体扭曲

柔性金属有机骨架（MOF）可以表现出出色的选择性和吸附CO _2的能力。将CO ₂掺入具有Cu ²⁺配位中心和有机支柱配体的柔性MOF中，会伴随由这些组分与CO ₂分子之间的化学相互作用引起的骨架晶格畸变。CO ₂吸附产生可重现的晶格膨胀，该膨胀可通过柱状配体的旋转实现。使用原位评估了Cu ₂（pzdc）₂（bpy）和Cu ₂（pzdc）₂（bpe），CPL-2和CPL-5的结构室温下在高达50 atm的CO ₂气压下进行同步辐射X射线粉末衍射。结构参数在加压和减压之间表现出滞后现象。由于柱状配体旋转和晶格的整体膨胀的结合，CPL-2和CPL-5中的孔体积在升高的CO ₂压力下增加。高达50 atm的体积CO ₂吸附测量结果表明，吸附行为与结构结果一致，包括在低压下迅速吸收CO _2，在20 atm以上达到饱和，以及在减压过程中保留CO _2的滞后现象。明显更高的CO ₂与基于CO ₂压力引起的可用于吸附的孔体积扩展的预测相比，在CPL-5中观察到了CPL-5的吸收，这表明CPL结构的柔韧性是增强吸附能力的关键因素。