Engineering Active Metal and Nonmetal Sites in Porous Structures of Metal‐Hydroxide Clusters for Enhanced D ₂ /H ₂ Uptake and Separation

Efficient deuterium separation from hydrogen isotopic mixtures poses a significant challenge due to the nearly identical physicochemical properties of D 2 and H 2 . Porous supramolecular assembly frameworks (SAFs) have emerged as promising candidates to address this issue, as their pore structures can be precisely tailored to achieve efficient hydrogen isotope separation. Herein, two metal‐hydroxide cluster‐based SAFs constructed from metal centers (Co 2+ and Cu 2+ ) coordinating with ligand L (HL = 1H‐benzo[f]isoindole‐1,3‐diimine) are reported. Solvothermal reaction of HL with Co(NO 3 ) 2 ·6H 2 O yielded [Co II 12 Co III 8 L 12 ( µ 3 ‐OH) 24 ]·12(NO 3 ) ( 1 ) which lacks active sites. In contrast, a similar reaction using Cu(ClO 4 ) 2 ·6H 2 O produced [Cu 20 L 8 ( µ 3 ‐OH) 24 (H 2 O) 8 ]·2(C 2 H 6 NH 2 )·5(ClO 4 )·2Cl·3(CHO 2 ) ( 2 ), featuring both active Cu 2+ and = NH. Activated 2 exhibits the second‐highest D 2 uptake of 301 cm 3 ·g ‒1 at 77 K and 100 kPa, significantly surpassing that of activated 1 (87 cm 3 ·g ‒1 ). Furthermore, activated 2 demonstrates exceptionally high D 2 /H 2 separation efficiency, with a D 2 retention time of 52 min·g ‒1 for a D 2 /H 2 /Ne mixture (2.5/2.5/95 vol.%) at a flow rate of 8 mL·min ‒1 . Computational analyses indicate that the superior D 2 /H 2 uptake and separation of activated 2 can be attributed to the synergistic effect of its active Cu 2+ and = NH. These findings offer a novel strategy for incorporating multiple active adsorption sites into porous SAFs to optimize D 2 /H 2 uptake and separation.