What can pKa and NBO charges of the ligands tell us about the water and thermal stability of metal organic frameworks?
What can pKa and NBO charges of the ligands tell us about the water and thermal stability of metal organic frameworks?
复制标题
配体的 pKa 和 NBO 电荷可以告诉我们有关金属有机骨架的水稳定性和热稳定性的哪些信息？
DOI：
10.1039/c4ta03154g
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发表时间：
2014-01-01
影响因子：
11.9
通讯作者：
Fang, Min
中科院分区：
文献类型：
--
作者：
Lu, Ping;Wu, Yong;Fang, Min
金属有机骨架（MOFs）的水热稳定性对于其在储氢和其他应用中的应用至关重要。在B3 LYP/6-31+ G（d，p）水平上，计算了298.15K时配体共轭酸的pK（a）（1）值和32个多羧酸配体和31个氮杂环配体配位原子的自然键轨道（NBO）电荷。使用SMD建模获得水溶液中的溶剂化吉布斯能（Δ G（solv））。基于气相中的优化结构计算NBO电荷。我们发现pK（a）（1）的计算值与一些已知的双齿配体的实验值有线性关系，而pK（a）（2）的计算值与实验值没有线性关系。结果表明，配体配位原子的NBO电荷与配体共轭酸的pK（a）（1）值一样，可以反映配体与金属离子的相对配位能力和M-L键的强度。据我们所知，系统计算多齿配体的pK（a）值和NBO电荷尚未报道。利用这种廉价的计算方法，计算结果可以很容易地扩展。根据计算结果，用M-L键强度和极性成功地解释了有关MOF材料水稳定性和热稳定性的一些实验结果。结果可用于预测目标MOF结构是否是水和热稳定的，预测已知MOF的水热稳定性，设计新的水热稳定的MOF，并基于计算的pK（a）值为合成程序提供指导。并给出了应用这些值的局限性。
The hydrothermal stability of metal organic frameworks (MOFs) is critical for their applications in hydrogen storage and other applications. The pK(a)(1) values of the conjugated acids of ligands and natural bond orbital (NBO) charges of the coordinating atoms of 32 multicarboxylate ligands and 31 N-heterocyclic ligands applied in the MOF syntheses were calculated at 298.15 K with the B3LYP/6-31+ G(d, p) level of calculations. Solvation Gibbs energies (Delta G(solv)) in aqueous solution were obtained using SMD modeling. NBO charges were calculated based on optimized structures in the gas phase. We found that the calculated pK(a)(1) values have a linear relationship with the experimental results of a few known bidentate ligands, but pK(a)(2) values do not. We demonstrated that NBO charges of the coordinating atoms of the ligands, like pK(a)(1) values of the conjugated acids of the ligands, can reflect the relative coordination abilities of the ligands to metal ions and the strength of the resulting M-L bonds. To the best of our knowledge, systematic calculations of the pK(a) values and NBO charges of multidentate ligands have not been reported. The calculated results can be easily expanded using this inexpensive calculation method. Some experimental results about water and thermal stability of MOF materials were successfully explained in terms of M-L bond strengths and polarity based on our calculated results. The results can be used to predict whether a targeted MOF structure would be water and thermally stable, predict the hydrothermal stability of known MOFs, design new hydrothermally stable MOFs and provide guidance for the synthetic procedures based on the calculated pK(a) values. The limitations of applying these values are also given.