Gradient Enhancement of Ligand Dipole Moment and Confinement Effect in Metal–Organic Frameworks for Boosting Sulfur Hexafluoride–Nitrogen Separation

Replacing pure SF 6 with SF 6 /N 2 mixtures curbs emissions but demands efficient low-concentration SF 6 recovery. We report a gradient enhancement strategy combining cis-trans isomerism and methylation to boost ligand dipole moment and confinement in three isostructural partitioned acs-MOFs ( ZJNU-181-trans, -cis, and -2Me ). Pre-synthesis DFT predictions of SF 6 affinity ( 2Me > cis > trans ) are validated experimentally. At 298 K and 10 kPa, SF 6 uptake follows 2Me > cis > trans, consistent with isosteric heats and IAST selectivity (169.8 for 2Me ). Breakthrough tests confirm this order, with 2Me showing the largest SF 6 /N 2 breakthrough gap (141.5 min g –1 ) and excellent recyclability. DFT reveals that methyl groups act as additional C–H···F donors while creating uniform 7.3 Å pores, synergistically enhancing SF 6 binding to –33.04 kJ mol –1 . This work establishes gradient dipole-confinement modulation as a generalizable MOF design paradigm.