Inorganic Node-Tuned Reticular Diversification of Metal–Organic Frameworks: Dual-Site Functionalization for Enhanced Methane Separation

Reticular chemistry offers a targeted and streamlined approach to synthesizing metal–organic frameworks (MOFs) through the assembly of predesigned molecular units. In this study, we investigated inorganic node-directed reticular diversification of MOFs by employing a nitrogen-containing aromatic polycarboxylate ligand as a fixed 4-connected organic node. By systematically tuning inorganic secondary building units (SBUs), various topological structures were obtained: the previously reported flu topology (derived from 8-connected nodes), dmc topology (from mixed 3,4-connected nodes), and a new pts-topology MOF ( ZJNU-409 ) built from Zn-based paddlewheel 4-connected nodes. ZJNU-409 possesses a three-dimensional framework containing one-dimensional channels and dual-site functionalization and shows excellent selective performance for C 2 H 6, C 3 H 8, C 2 H 2, and CO 2 over CH 4 . Ideal adsorbed solution theory (IAST) calculations yielded selectivities of 135 for C 3 H 8 /CH 4, 26 for C 2 H 6 /CH 4, 100 for C 2 H 2 /CH 4, and 29 for CO 2 /CH 4 . Fixed-bed breakthrough experiments confirmed that C 2 H 6, C 3 H 8, C 2 H 2, and CO 2 had retention times longer than those of CH 4, and grand canonical Monte Carlo (GCMC) calculations confirmed stronger interactions between the framework and these gases compared to CH 4 . These results collectively underscore the potential of ZJNU-409 for efficient methane purification applications.