Engineering Active Metal and Nonmetal Sites in Porous Structures of Metal-Hydroxide Clusters for Enhanced D₂/H₂...

Efficient deuterium separation from hydrogen isotopic mixtures poses a significant challenge due to the nearly identical physicochemical properties of D₂ and H₂. 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 (Co²⁺ and Cu²⁺) coordinating with ligand L (HL = 1H-benzo[f]isoindole-1,3-diimine) are reported. Solvothermal reaction of HL with Co(NO₃)₂·6H₂O yielded [Co^II ₁₂Co^III ₈L₁₂(µ₃-OH)₂₄]·12(NO₃) (1) which lacks active sites. In contrast, a similar reaction using Cu(ClO₄)₂·6H₂O produced [Cu₂₀L₈(µ₃-OH)₂₄(H₂O)₈]·2(C₂H₆NH₂)·5(ClO₄)·2Cl·3(CHO₂) (2), featuring both active Cu²⁺ and = NH. Activated 2 exhibits the second-highest D₂ uptake of 301 cm³·g^‒1 at 77 K and 100 kPa, significantly surpassing that of activated 1 (87 cm³·g^‒1). Furthermore, activated 2 demonstrates exceptionally high D₂/H₂ separation efficiency, with a D₂ retention time of 52 min·g^‒1 for a D₂/H₂/Ne mixture (2.5/2.5/95 vol.%) at a flow rate of 8 mL·min^‒1. Computational analyses indicate that the superior D₂/H₂ uptake and separation of activated 2 can be attributed to the synergistic effect of its active Cu²⁺ and = NH. These findings offer a novel strategy for incorporating multiple active adsorption sites into porous SAFs to optimize D₂/H₂ uptake and separation.