The family of diamine-appended metal–organic frameworks exemplified by compounds of the type mmen–M₂(dobpdc) (mmen = N,N′-dimethylethylenediamine; M = Mg, Mn, Fe, Co, Zn; dobpdc⁴⁻ = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) are adsorbents with significant potential for carbon capture, due to their high working capacities and strong selectivity for CO₂ that stem from a cooperative adsorption mechanism. Herein, we use first-principles density functional theory (DFT) calculations to quantitatively investigate the role of mmen ligands in dictating the framework properties. Our van der Waals-corrected DFT calculations indicate that electrostatic interactions between ammonium carbamate units significantly enhance the CO₂ binding strength relative to the unfunctionalized frameworks. Additionally, our computed energetics show that mmen–M₂(dobpdc) materials can selectively adsorb CO₂ under humid conditions, in agreement with experimental observations. The calculations further predict an increase of 112% and 124% in the orientationally-averaged Young's modulus E and shear modulus G, respectively, for mmen–Zn₂(dobpdc) compared to Zn₂(dobpdc), revealing a dramatic enhancement of mechanical properties associated with diamine functionalization. Taken together, our calculations demonstrate how functionalization with mmen ligands can enhance framework gas adsorption and mechanical properties.

中文翻译：

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M ₂（dobpdc）金属-有机骨架的二胺官能化后 ，CO ₂结合力和机械性能的增强†

带有二胺的金属有机骨架家族，以mmen-M ₂（dobpdc）类型的化合物为例（mmen = N，N'-二甲基乙二胺； M = Mg，Mn，Fe，Co，Zn； dobpdc ^4- = 4 （4'-dioxidobiphenyl-3,3'-dicarboxylate）是吸附剂，由于其高工作能力和对CO _2的强选择性而具有很强的碳捕获潜力。这源于协同吸附机制。在这里，我们使用第一原理密度泛函理论（DFT）计算来定量研究mmen配体在决定骨架性质中的作用。我们的范德华校正DFT计算表明，相对于未官能化的骨架，氨基甲酸铵单元之间的静电相互作用显着增强了CO _2的结合强度。另外，我们的计算的能量学表明，mmen–M ₂（dobpdc）材料可以在潮湿条件下选择性吸附CO ₂，这与实验观察一致。该计算进一步预测了取向平均杨氏模量E和剪切模量的112％和124％的增加ģ，分别用于mmen-Zn系₂（dobpdc）相比对于Zn ₂（dobpdc），揭示了用二胺官能化相关的机械性能的显着提高。两者合计，我们的计算证明了mmen配体的官能化如何增强骨架气体的吸附和机械性能。