Dual-Orbital Synergy in Paired Cu(II) Open Metal Sites for Enhanced High-Temperature Hydrogen Isotope Separation

The selective separation of hydrogen isotopes under mild cryogenic conditions remains a formidable challenge due to their nearly identical physicochemical properties. Here, we report a dual strategy of pore topology design and bimetallic synergistic engineering to amplify chemical affinity quantum sieving (CAQS). Among three tailored Cu(II)-MOFs (Cu-bptc, Cu-mbtc, Cu-ATC), Cu-ATC exhibited exceptional performance, achieving a D₂/H₂ selectivity of 20 at 50 K (10 mbar) and 1.8 in breakthrough experiments at 77 K, surpassing all reported Cu-MOFs. The ultramicroporous topology of Cu-ATC fixes a Cu···Cu distance of 5.98 Å within one-dimensional channels (~5.6 Å), while Jahn–Teller distortion induces axial elongation at each Cu(II) center, stabilizing the d _z ² orbitals and enhancing their availability for interaction with hydrogen isotope molecules. This dual effect creates two closely spaced open metal sites that can simultaneously interact with H ₂ and D ₂ , amplifying their differential interactions and thereby driving isotope separation via CAQS. The distinct binding strength is evidenced by in situ DRIFTS (H–H stretch red-shift of 682 cm ^-1 ) and by DFT calculations showing stronger adsorption of D₂ (−15.8 kJ mol ^-1 at the primary site). These microscopic differences account for the observed D ₂ /H ₂ selectivity, highlighting a new paradigm for CAQS-based isotope separation under mild cryogenic conditions.