Structural Characterisation of Metal-Organic Frameworks using Solid-State NMR Spectroscopy

微孔和纳米孔固体是现代化学中最令人兴奋的一类材料，它们具有与小分子相似大小的孔和高内表面积。这导致了气体储存和分离以及药物输送的应用，孔隙可以作为催化纳米级反应容器，这些材料的结构与任何应用都密切相关，详细的原子水平知识对于控制性能和开发新用途至关重要。核磁共振波谱对局部环境的敏感性，不需要任何远程顺序，使其成为研究这些复杂材料的理想工具。在这个项目中，我们将专注于金属-有机框架的表征，其中有机连接分子连接由金属原子或金属簇组成的节点。这些材料表现出比沸石更多的结构多样性，有机连接分子的拓扑结构、大小和化学功能可以变化，就像存在的金属类型一样。金属中心不仅影响最终材料的化学性质，而且影响小分子吸附后获得的结构形式。提出的工作将集中在两个关键领域：(1)利用17O固态核磁共振光谱研究混合金属mof。这将涉及开发新的合成方法，以经济高效地富集17O（其自然丰度仅为0.037%）mof的原子效率。这项工作还需要实施和优化高分辨率的17O固态核磁共振实验（以及研究提高其灵敏度的方法）。这些方法将用于研究混合金属mof的组成和无序性，以及在吸附客体分子时发生的任何结构变化。(2)顺磁性mof的核磁共振波谱。许多重要的mof含有顺磁性金属中心，如Cu2+、Co2+或Mn2+。这类材料的核磁共振波谱受到未成对电子和核自旋之间极强耦合的阻碍，需要专门的实验方法来获取光谱。这项工作将开发一种基于快速样品旋转、快速信号平均和使用自旋回波的顺磁性mof的频谱采集协议。然后，这将应用于客体分子吸附的研究，最初是在模型cu基MOF （HKUST-1）中，以及一系列新的功能化MOF（基于tam -1）的结构表征，这些MOF显示出有趣的双重吸附特性。

Microporous and nanoporous solids are one of the most exciting classes of materials in modern chemistry, possessing pores of similar sizes to small molecules and high internal surface areas. This leads to applications in gas storage and separation and drug delivery and the pores can act as nanosize reaction vessels in catalysis, The structure of these materials is intimately connected with any application, and a detailed atomic-level knowledge of this is vital to controlling properties and developing new uses. The sensitivity of NMR spectroscopy to the local environment, without the need for any long-range order, makes it an ideal tool for studying these complex materials. In this project we will focus on the characterisation of metal-organic frameworks, where an organic linker molecule connects nodes composed of metal atoms or metal clusters. These materials exhibit much more structural variety than zeolites, with the topology, size and chemical functionality of the organic linker molecules able to vary, as can the type(s) of metal present. The metal centres affect not only the chemical properties of the final material, but also the structural forms obtained upon adsorption of small molecules.The work proposed will focus on two key areas:(1) Using 17O solid-state NMR spectroscopy to investigate mixed-metal MOFs. This will involve the development of new synthetic procedures for cost-effective and atom-efficient isotopic enrichment of MOFs in 17O (which has a natural abundance of only 0.037%). The work will also require the implementation and optimisation of high-resolution 17O solid-state NMR experiments (and the investigation of methods to improve their sensitivity). These methods will then be employed to investigate the composition and disorder in mixed-metal MOFs, and any structural changes that take place upon the adsorption of guest molecules. (2) NMR spectroscopy of paramagnetic MOFs.Many important MOFs contain paramagnetic metal centres, e.g., Cu2+, Co2+ or Mn2+. NMR spectroscopy of such materials is hampered by the extremely strong coupling between the unpaired electron and the nuclear spin, necessitating specialist experimental approaches for spectral acquisition. This work will develop a protocol for spectral acquisition of paramagnetic MOFs, based on fast sample spinning, rapid signal averaging and the use of spin echoes. This will then be applied to the study of the adsorption of guest molecules, initially in a model Cu-based MOF (HKUST-1), and to the structural characterisation of a series of new functionalised MOFs (based on STAM-1) which display interesting dual adsorption properties.