Wanli Zhang , Shoushun Chen , Victor V. Terskikh , Bryan E.G. Lucier , Yining Huang
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引用次数: 1
Abstract
Metal-organic frameworks (MOFs) are emerging materials with many current and potential applications due to their unique properties. One critical feature is that the physical and chemical properties of MOFs are tunable. One of the methods for tuning MOF properties is to introduce defects by design for desired applications. Characterization of MOF defects is important, but very challenging due to the local nature and short-range ordering. In this work, we have introduced the ordered vacancies (the defects) in the form of the coordinatively unsaturated sites (CUSs) into the framework of MOF MIL-120(Al). The creation of ordered vacancies is achieved by replacing one quarter of the BTEC (1,2,4,5-benzenetetracarboxylate) with BDC (benzene-1,4-dicarboxylate) linkers. Both parent and defective MOFs were characterized by multinuclear solid-state NMR spectroscopy. 1H MAS NMR is used to characterize the hydrogen bonding in these MOFs, whereas 13C CP MAS NMR confirms unambiguously that the BDC is incorporated into the framework. One-dimensional 27Al MAS NMR provides direct evidence of the coordinatively unsaturated Al sites (the defects). Furthermore, 27Al 3QMAS experiments at 21.1 T allow direct identification of one penta-coordinated and three chemically inequivalent octahedral Al sites in the defective MIL-120(Al). Two of the above-mentioned octahedral Al sites are in the domain which appears defect-free. The third octahedral Al site is near the defective site. This work clearly demonstrates the power of solid-state NMR spectroscopy for characterization of defective MOFs.
金属有机骨架(MOFs)是一种新兴材料,由于其独特的性能,具有广泛的应用前景。mof的一个关键特征是其物理和化学性质是可调的。调整MOF特性的方法之一是通过设计引入缺陷以满足所需的应用。MOF缺陷的表征是很重要的,但由于局部性质和短程有序,非常具有挑战性。在这项工作中,我们将协调不饱和位(CUSs)形式的有序空位(缺陷)引入MOF MIL-120(Al)的框架中。通过用BDC(苯-1,4-二羧酸酯)连接剂取代四分之一的BTEC(1,2,4,5-苯四羧酸酯)来实现有序空位的产生。母mof和缺陷mof都用多核固体核磁共振光谱进行了表征。1H MAS NMR用于表征这些mof中的氢键,而13C CP MAS NMR明确证实BDC被纳入框架。一维27Al MAS NMR提供了配位不饱和Al位(缺陷)的直接证据。此外,21.1 T的27Al 3QMAS实验允许在缺陷MIL-120(Al)中直接识别一个五配位和三个化学不平等的八面体Al位点。上述八面体Al中有两个位点处于无缺陷的区域。第三个八面体Al位点在缺陷位点附近。这项工作清楚地证明了固态核磁共振光谱表征缺陷mof的能力。
期刊介绍:
The journal Solid State Nuclear Magnetic Resonance publishes original manuscripts of high scientific quality dealing with all experimental and theoretical aspects of solid state NMR. This includes advances in instrumentation, development of new experimental techniques and methodology, new theoretical insights, new data processing and simulation methods, and original applications of established or novel methods to scientific problems.