Understanding the behaviour of flexible metal–organic frameworks (MOFs)—porous crystalline materials that undergo a structural change upon exposure to an external stimulus—underpins their design as responsive materials for specific applications, such as gas separation, molecular sensing, catalysis and drug delivery. Reversible transformations of a MOF between open- and closed-pore forms—a behaviour known as ‘breathing’—typically occur through well-defined crystallographic transitions. By contrast, continuous breathing is rare, and detailed characterization has remained very limited. Here we report a continuous-breathing mechanism that was studied by single-crystal diffraction in a MOF with a diamondoid network, (Me₂NH₂)[In(ABDC)₂] (ABDC, 2-aminobenzene-1,4-dicarboxylate). Desolvation of the MOF in two different solvents leads to two polymorphic activated forms with very different pore openings, markedly different gas-adsorption capacities and different CO₂ versus CH₄ selectivities. Partial desolvation introduces a gating pressure associated with CO₂ adsorption, which shows that the framework can also undergo a combination of stepped and continuous breathing.

中文翻译：

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类金刚石金属-有机骨架中溶剂可切换的连续呼吸行为及其对CO2和CH4选择性的影响

了解柔性金属有机框架（MOF）的行为-暴露于外部刺激下会发生结构变化的多孔晶体材料-可以将其设计为适用于特定应用的响应材料，例如气体分离，分子传感，催化和药物输送。MOF在开孔和闭孔形式之间的可逆转换（一种称为“呼吸”的行为）通常是通过明确定义的晶体学转换发生的。相比之下，连续呼吸很少见，并且详细的特征描述仍然非常有限。在这里，我们报告了一种连续呼吸机制，该机制是通过在具有菱形网络的（MO ₂ NH ₂）[In（ABDC）₂]（ABDC，2-氨基苯-1,4-二羧酸酯）。MOF在两种不同溶剂中的去溶剂化导致两种多晶型活化形式具有非常不同的开孔，明显不同的气体吸附能力以及不同的CO ₂与CH ₄选择性。部分去溶剂化会引入与CO ₂吸附相关的门控压力，这表明构架也可以经历分步呼吸和连续呼吸的组合。