Exploring Structural Disorders in Aluminum-Containing Metal–Organic Frameworks: Comparison of Solid-State 27Al NMR Powder Spectra to DFT Calculations on Bulk Periodic Structures,The Journal of Physical Chemistry C

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Exploring Structural Disorders in Aluminum-Containing Metal–Organic Frameworks: Comparison of Solid-State 27Al NMR Powder Spectra to DFT Calculations on Bulk Periodic Structures
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-05-19 , DOI: 10.1021/acs.jpcc.0c03000
Oleg V. Petrov ₁ , Vojtěch Chlan ₁ , Jan Rohlíček ₂ , Jan Demel ₃ , Jozef Veselý ₄ , Jan Lang ₁

Affiliation

We use solid-state ²⁷Al NMR spectroscopy to test four aluminum-based metal–organic framework (MOF) materials—ICR-2, ICR-4, ICR-6, and ICR-7—against their structural models obtained from electron and X-ray diffraction. The lineshape analysis of the ²⁷Al NMR spectra reveals varying degrees of disorders in the Al coordination environment, depending on the sample, which we were able to parameterize in terms of the extended Czjzek model (ECM) of the electric field gradient (EFG) distribution. The model’s degree-of-disorder parameter ε was found to correlate inversely with the crystallite size of the MOFs. This suggests that the EFG distribution is related to a high surface-to-volume ratio of the particles and can be ascribed to the deviation of molecular arrangements near the surface from the bulk crystalline order. The ECM’s parameters for a fixed part of the EFG tensor, a quadrupolar coupling constant C_Q,0 and asymmetry parameter η₀, were compared to the EFG parameters calculated on fully periodic models using density functional theory (DFT). The DFT-calculated C_Q was found to exceed C_Q,0 by 25–60%, depending on the MOF. Although this result finds support in the literature, an explanation of such apparent spectral narrowing is still lacking.

中文翻译：

探索含铝金属-有机骨架中的结构紊乱：固态²⁷ Al NMR粉末光谱与本体周期结构的DFT计算的比较

我们使用固态²⁷ Al NMR光谱测试了四种铝基金属-有机骨架（MOF）材料（ICR-2，ICR-4，ICR-6和ICR-7），以及从电子和X获得的结构模型射线衍射。²⁷的线形分析Al NMR光谱揭示了Al配位环境中不同程度的无序，具体取决于样品，我们能够根据电场梯度（EFG）分布的扩展Czjzek模型（ECM）进行参数化。发现模型的无序度参数ε与MOF的微晶尺寸成反比。这表明EFG分布与颗粒的高表面体积比有关，并且可以归因于表面附近的分子排列与块状晶体顺序的偏离。ECM的用于EFG张量，四极耦合常数的固定部分参数Ç _Q，0和不对称参数η ₀，与使用密度泛函理论（DFT）在全周期模型上计算的EFG参数进行了比较。根据MOF，DFT计算得出的C _Q超过C _Q，0 25-60％。尽管这一结果在文献中得到了支持，但仍缺乏对这种明显光谱变窄的解释。

更新日期：2020-05-19

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