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高分辨率固态 13C NMR 光谱法研究顺磁金属有机骨架 STAM-1 和 HKUST-1。

High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1.

机构信息

School of Chemistry and EaStCHEM, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK.

出版信息

Phys Chem Chem Phys. 2013 Jan 21;15(3):919-29. doi: 10.1039/c2cp43445h.

Abstract

Solid-state (13)C magic-angle spinning (MAS) NMR spectroscopy is used to investigate the structure of the Cu(II)-based metal-organic frameworks (MOFs), HKUST-1 and STAM-1, and the structural changes occurring within these MOFs upon activation (dehydration). NMR spectroscopy is an attractive technique for the investigation of these materials, owing to its high sensitivity to local structure, without any requirement for longer-range order. However, interactions between nuclei and unpaired electrons in paramagnetic systems (e.g., Cu(II)-based MOFs) pose a considerable challenge, not only for spectral acquisition, but also in the assignment and interpretation of the spectral resonances. Here, we exploit the rapid T(1) relaxation of these materials to obtain (13)C NMR spectra using a spin-echo pulse sequence at natural abundance levels, and employ frequency-stepped acquisition to ensure uniform excitation of resonances over a wide frequency range. We then utilise selective (13)C isotopic labelling of the organic linker molecules to enable an unambiguous assignment of NMR spectra of both MOFs for the first time. We show that the monomethylated linker can be recovered from STAM-1 intact, demonstrating not only the interesting use of this MOF as a protecting group, but also the ability (for both STAM-1 and HKUST-1) to recover isotopically-enriched linkers, thereby reducing significantly the overall cost of the approach.

摘要

固态 (13)C 魔角旋转 (MAS) NMR 光谱用于研究基于 Cu(II)的金属有机骨架 (MOF),HKUST-1 和 STAM-1 的结构,以及这些 MOF 在活化(脱水)过程中发生的结构变化。NMR 光谱是研究这些材料的一种有吸引力的技术,因为它对局部结构具有高灵敏度,而不需要长程有序。然而,在顺磁体系(例如基于 Cu(II)的 MOF)中核与不成对电子之间的相互作用不仅对光谱采集构成了相当大的挑战,而且对光谱共振的分配和解释也构成了相当大的挑战。在这里,我们利用这些材料快速的 T(1)弛豫,在自然丰度水平下使用自旋回波脉冲序列获得 (13)C NMR 光谱,并采用频率步进采集方法确保在宽频率范围内均匀激发共振。然后,我们利用有机连接分子的选择性 (13)C 同位素标记,首次能够明确分配这两种 MOF 的 NMR 光谱。我们表明,从 STAM-1 中可以完整回收单甲基化连接分子,这不仅证明了这种 MOF 作为保护基团的有趣用途,而且还证明了 STAM-1 和 HKUST-1 都能够回收同位素富集的连接分子,从而大大降低了该方法的总体成本。

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