A MOF-505 Analogue Based on a Thiazolothiazole Diisophthalate for High-Capacity C₂H₂ Separation and Purification

The efficient separation of C₂H₂ from CO₂ and CH₄ remains challenging due to their similar molecular sizes and physical properties. Herein, we report a NbO-type metal-organic framework (MOF) (ZJNU-170) constructed from a thiazolothiazole-based diisophthalate ligand and Cu²⁺ paddlewheel units. The thiazolothiazole heterocycle serves as a hydrogen bond acceptor, enabling C-H···N and C-H···S interactions with C₂H₂. Benefiting from this design, ZJNU-170a exhibits a high C₂H₂ uptake of 237.1 cm³ (STP) g^-1 at 278 K and 1 atm, with a moderate isosteric heat of adsorption of 30.7 kJ mol^-1, achieving a favorable balance between affinity and regenerability. IAST selectivity calculations at 298 K and 1 atm for equimolar mixtures give values of 4.4 for C₂H₂/CO₂ and 29.6 for C₂H₂/CH₄. Dynamic breakthrough experiments confirm practical separation performance for binary and ternary mixtures, delivering high-purity CH₄ (>99.95%) and C₂H₂ (>99.8%) under ambient conditions. Density functional theory (DFT) calculations reveal that open metal sites serve as primary adsorption sites via π-coordination, while thiazolothiazole units provide additional hydrogen-bonding interactions. Collectively, this work presents a promising adsorbent for energy-efficient C₂H₂ purification and offers insights into the rational design of NbO-type MOFs for multicomponent gas separation.