The pressing need to lower atmospheric carbon dioxide (CO₂) concentration has captivated global focus on point-source capture and transformation of this greenhouse gas to chemicals. Purpose-driven pore-functionality engineering in metal–organic frameworks (MOFs) can lead to high-temperature and humid-condition adsorption and efficient cycloaddition of CO₂ and further assist in achieving unconventional methodologies for sustainable tandem catalysis. Herein, we develop a [Zn₂(COO)₄N₄] building unit-containing chemo-robust framework with carboxamide functionality, free oxygen atoms, and π-electron-rich moieties affixed to one-dimensional channels. This 3-fold entangled MOF exhibits strong framework–gas interactions and unveils variable-temperature CO₂ adsorption with recurrent capture–release cycles even under 75% relative humidity. Interestingly, the CO₂/N₂ selectivity shows a remarkable 82% increase with an increase in the temperature from 273 K (79) to 313 K (143), which overpowers several porous adsorbents and validates potential of this MOF in flue gas separation. This microporous MOF catalyzes solvent-free and recyclable CO₂ cycloaddition with various epoxides under atmospheric pressure. In contrast to the classical Lewis acid-mediated reaction, controlled experiments, including performance comparison of a urea functionality-truncated isostructural framework corroborate the unique two-point hydrogen bonding-mediated cycloaddition pathway. The suitably oriented carboxamide moiety within the MOF channels further acts as a hydrogen bond donor (HBD) site in the tandem deacetalization–Knoevenagel condensation reaction with >99% conversion under solvent-less mild conditions in 4 h. The cooperative role of acid–base dual sites in substrate activation is comprehensively supported by studies using external additives, fluoro-titration-derived interactions, and comparison with an unfunctionalized framework. To the best of our knowledge, in this one-pot reaction, acetals having larger molecular dimensions exhibit poor formation of α,β-unsaturated dicyanides, and demonstrate pore-fitting-mediated size-exclusive catalysis.

中文翻译：

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在具有羧酰胺官能团的常压环加成和尺寸独有的串联 Knoevenagel 缩合的缠结金属有机框架中进行温变 CO2 分离


降低大气中二氧化碳 （CO₂） 浓度的迫切需求引起了全球对点源捕获和将这种温室气体转化为化学品的关注。金属有机框架 （MOF） 中以目的为导向的孔功能工程可以导致 CO₂ 的高温和潮湿条件下的吸附和有效的环加成反应，并进一步有助于实现可持续串联催化的非常规方法。在此，我们开发了一个包含 [Zn₂（COO）₄N₄] 构建单元的化学稳健框架，该框架具有羧酰胺官能团、游离氧原子和附着在一维通道上的富π电子部分。这种 3 重纠缠 MOF 表现出很强的框架-气体相互作用，即使在 75% 的相对湿度下，也能通过循环捕获-释放循环揭示可变温度的 CO₂ 吸附。有趣的是，当温度从 273 K （79） 升高到 313 K （143） 时，CO₂/N₂ 选择性显著增加了 82%，这压倒了几种多孔吸附剂，并验证了这种 MOF 在烟气分离中的潜力。这种微孔 MOF 在大气压下催化无溶剂且可回收的 CO₂ 环加成反应与各种环氧化物。与经典的 Lewis 酸介导的反应相比，对照实验，包括尿素功能截短等结构框架的性能比较，证实了独特的两点氢键介导的环加成途径。 MOF 通道内适当取向的羧酰胺部分在串联脱乙酰化-Knoevenagel 缩合反应中进一步充当氢键供体 （HBD） 位点，在无溶剂温和条件下在 4 小时内以 >99% 的转化率。使用外部添加剂、荧光滴定衍生的相互作用以及与非功能化框架的比较的研究全面支持酸碱双位点在底物活化中的协同作用。据我们所知，在这种一锅反应中，具有较大分子尺寸的缩醛表现出 α，β-不饱和二氰化物的不良形成，并表现出孔拟合介导的尺寸异位催化。