Pore Environment Optimization of Microporous Metal-Organic Frameworks with Huddled Pyrazine Pillars for C2H2/CO2 Separation.

Metal-organic frameworks (MOFs) have been proven promising in addressing many critical issues related to gas separation and purification. However, it remains a great challenge to optimize the pore environment of MOFs for purification of specific gas mixtures. Herein, we report the rational construction of three isostructural microporous MOFs with the 4,4',4"-tricarboxyltriphenylamine (H3TCA) ligand, unusual hexaprismane Ni6O6 cluster, and functionalized pyrazine pillars [PYZ-x, x = -H (DZU-10), -NH2 (DZU-11), and -OH (DZU-12)], where the building blocks of Ni6O6 clusters and huddled pyrazine pillars are reported in porous MOFs for the first time. These building blocks have enabled the resulting materials to exhibit good chemical stability and variable pore chemistry, which thus contribute to distinct performances toward C2H2/CO2 separation. Both single-component isotherms and dynamic column breakthrough experiments demonstrate that DZU-11 with the PYZ-NH2 pillar outperforms its hydrogen and hydroxy analogues. Density functional theory calculations reveal that the higher C2H2 affinity of DZU-11 over CO2 is attributed to multiple electrostatic interactions between C2H2 and the framework, including strong C≡C···H-N (2.80 Å) interactions. This work highlights the potential of pore environment optimization to construct smart MOF adsorbents for some challenging gas separations.