Heptanuclear Fluorido-Bridged Cobalt Metal−Organic Frameworks Containing BF ₄ ⁻ Counteranions for Highly Selective C ₂ H ₂ /CO ₂ Separation

The separation of C 2 H 2 and CO 2 is highly challenging owing to their similar molecular sizes and physicochemical properties. Herein, we report two isostructural metal−organic frameworks, LIFM-712 and LIFM-713, constructed from fluorido-bridged heptanuclear [Co 7 F 12 ] 2+ clusters and tritopic pyridyl ligands, which feature a pyr topology. Confined BF 4 − counteranions synergize with bridging fluorido ligands to generate fluorine-rich pore environments, thus providing abundant C−H···F recognition sites for C 2 H 2 . LIFM-712 exhibits stronger C 2 H 2 binding ( Q st = 35.2 kJ mol −1 ), whereas LIFM-713 balances affinity and specific surface area, achieving a higher C 2 H 2 uptake of 149.8 cm 3 g −1 at 298 K and 1 bar. For LIFM-713, ideal adsorbed solution theory calculations afford a C 2 H 2 /CO 2 selectivity up to 4.5, and breakthrough experiments demonstrate a clear separation with a 35 min g −1 separation window at 298 K. For the two Co-MOFs, theoretical simulations and in situ infrared spectra reveal that cooperative interactions between cluster-bound fluorido sites and pore-confined counteranions govern the selective adsorption of C 2 H 2 . This work highlights a synergistic fluorine-functionalization strategy for designing efficient adsorbents for challenging gas separations.