High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1
High-resolution solid-state 13C NMR spectroscopy of the paramagnetic metal-organic frameworks, STAM-1 and HKUST-1
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DOI：
10.1039/c2cp43445h
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Ashbrook, Sharon E.
中科院分区：
文献类型：
--
作者：
Dawson, Daniel M.;Jamieson, Lauren E.;Ashbrook, Sharon E.
用固体C-13魔角旋转(MAS)核磁共振研究了铜(II)基金属有机骨架(MOF)、HKUST-1和STAM-1的结构，以及这些MOF在活化(脱水)过程中的结构变化。核磁共振波谱是研究这些材料的一种很有吸引力的技术，因为它对局部结构高度敏感，不需要更长的有序度。然而，在顺磁体系(例如，基于铜(II)的MOF)中，核与未成对电子之间的相互作用不仅对光谱的获取，而且对光谱共振的归属和解释都构成了相当大的挑战。在这里，我们利用这些材料的快速T-1弛豫，在自然丰度水平下使用自旋回波脉冲序列获得C-13核磁共振谱，并使用频率步进采集来确保在较宽的频率范围内均匀激发共振。然后，我们利用有机连接物分子的选择性碳-13同位素标记，首次明确指定了两个MOF的核磁共振谱。我们证明了单甲基化接头可以完整地从STAM-1中回收，这不仅展示了这种MOF作为保护基的有趣用途，而且(对于STAM-1和HKUST-1)回收同位素丰富的接头的能力，从而显著降低了该方法的总体成本。
Solid-state C-13 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 C-13 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 C-13 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.