Abstract: Efficient capture of the greenhouse gas nitrous oxide (N2O) is of great significance for mitigating climate change and resource recovery. In this study, two guanidinium-based hydrogen-bonded organic frameworks (HOFs) with pyridyl nitrogen site isomerism, namely G-5,5'-BPyDC and G-4,4'-BPyDC, were successfully constructed using 2,2'-bipyridine-5,5'-dicarboxylic acid and 2,2'-bipyridine-4,4'-dicarboxylic acid as ligands. The effects of ligand structure on the hydrogen-bonded network, pore environment, and N2O/N2 adsorption and separation performance were systematically investigated by single-crystal X-ray diffraction, thermogravimetric analysis, Hirshfeld surface analysis, and gas adsorption experiments. The results showed that both frameworks were constructed via N-H…O hydrogen bonds. However, the asymmetric unit of G-5,5'-BPyDC contained two methanol molecule, and its free volume and surface area were larger than those of G-4,4'-BPyDC, while the latter exhibited a more compact molecular packing. Both materials exhibited an decomposition temperature above 290℃, showing good thermal stability. Hirshfeld surface analysis revealed that the total contribution of O-H/H-O and N-H/H-N hydrogen bonds in G-5,5'-BPyDC (32.0%) was higher than that in G-4,4'-BPyDC (29.7%). At 25℃ and 4.0 MPa, the N2O adsorption capacity of G-5,5'-BPyDC was 2.32 mmol/g, higher than that of G-4,4'-BPyDC (2.02 mmol/g). IAST calculations indicate that the selectivities of G-5,5'-BPyDC for N2O/N2 (50∶50 and 10∶90) mixtures reached 29.26 and 111.32, respectively, significantly superior to those of G-4,4'-BPyDC (6.61 and 17.03). In conclusion, pyridyl nitrogen site isomerism can effectively optimize N2O/N2 adsorption and separation performance by modulating the pore polarity and hydrogen-bonded network of the frameworks, providing a new strategy for isomer design.

Key words: hydrogen-bonded organic frameworks, guanidinium-based materials, pyridinic nitrogen site isomerism, N2O/N2 adsorption separation

摘要： 高效捕获温室气体一氧化二氮(N2O)对缓解温室效应、实现资源回收具有重要意义。本工作以2,2'-联吡啶-5,5'-二羧酸和2,2'-联吡啶-4,4'-二羧酸为配体，成功构筑了两种吡啶氮位点异构的胍基氢键有机框架(HOFs)——2,2'-联吡啶-5,5'-二羧酸胍(G-5,5'-BPyDC)和2,2'-联吡啶-4,4'-二羧酸胍(G-4,4'-BPyDC)。通过单晶X射线衍射、热重分析、Hirshfeld表面分析及气体吸附实验，系统研究了配体结构异构对氢键网络、孔道环境及N2O/N2吸附分离性能的影响。结果表明，两种HOFs均通过N-H…O氢键构筑三维框架结构：G-5,5'-BPyDC的不对称单元含两个甲醇分子，其自由体积和表面积大于G-4,4'-BPyDC，而后者分子堆积更为紧密；两种材料的起始分解温度均≥290℃，表现出良好的热稳定性。Hirshfeld表面分析显示，G-5,5'-BPyDC中O-H/H-O与N-H/H-N氢键总贡献(32.0%)高于G-4,4'-BPyDC (29.7%)。气体吸附测试表明，在25℃, 4.0 MPa条件下，G-5,5'-BPyDC对N2O的吸附容量为2.32 mmol/g，高于G-4,4'-BpyDC (2.02 mmol/g)。IAST计算结果显示，G-5,5'-BPyDC对N2O/N2 (50∶50和10∶90)混合气的选择性分别达29.26和111.32，显著优于G-4,4'-BPyDC (6.61和17.03)。综上，吡啶氮位点异构可通过调控框架孔道极性及氢键网络，有效优化N2O/N2吸附分离性能，该研究为异构体设计策略提供了新思路。

关键词: 氢键有机框架, 胍基材料, 吡啶氮位点异构, N2O/N2吸附分离