A 3D polymorphic Cu-based ultramicroporous MOF capable of CO2 Uptake and Conversion

Abstract

The development of advanced porous sorbents for CO₂ capture from gas mixtures remains pivotal for meeting net zero-emission targets by 2050. Among these, metal–organic frameworks (MOFs) continue to stand out due to their structural tunability and high surface areas. Herein, we report a new ultramicroporous 3D physisorbent MOF, constructed from Cu^II nodes and a multitopic 3,6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone anilato ligand (trz₂An). This species, of the [Cu(trz₂An)]·nH₂O (n ≤ 3) general formula, crystallizes in two (monoclinic and orthorhombic) polymorphs. The existence of two structurally related forms arises from a polysynthetic twinning mechanism involving short range ligand reorientation within a single crystal domain. Despite such structural variability, comparative analysis of both polymorphs reveals no significant differences in porosity metrics or gas sorption behavior. [Cu(trz₂An)] displays high selectivity and separation efficiency for N₂/CO₂ and CH₄/CO₂ mixtures, along with remarkable cycling stability. Furthermore, it shows promising catalytic activity toward the CO₂ reduction reaction (CO₂RR), which plays a key role in carbon utilization strategies, particularly favouring the formation of ethylene — an industrially valuable product. These results highlight [Cu(trz₂An)]·as a regenerable, structurally resilient MOF, combining efficient gas separation and CO₂ valorization and offering a compelling blueprint for the design of next-generation, environmentally sustainable physisorbents.