Quantifying the Dynamic Response in Metal-Organic Frameworks (MOFs): A Platform for Tuning Chemical Space in Porous Materials

金属有机骨架(MOF)是一种具有分子尺度气孔的周期性晶体材料，是一系列科学和工程学科中研究最广泛的材料类别之一。它们的模块化结构由有机配体连接的含金属离子的节点组成，使空间和化学调节都能够选择性地捕获孔隙空间中的分子。这些特性使MOF的性能可以针对各种应用进行优化，包括气体存储和分离、分子检测、环境修复、催化和药物输送。因此，它们的潜在影响横跨能源、交通、环境和医疗保健部门。MOF的周期性结晶性质使它们易于通过衍射方法进行原子水平的表征，并通过各种光谱技术进行广泛的表征，这些技术共同提供了与材料设计和优化有关的更多细节，而不是活性碳等非晶态竞争材料。与沸石和类似的氧化物材料相比，MOF还表现出了优势，因为MOF是由金属离子和有机配体组成的模块化结构，合成后化学修饰的机会使其在孔大小、孔形状和化学官能团的空间排列方面具有几乎无限的多样性。在过去的20年里，已经报道了数千个MOF中的大约10个。大多数MOF具有固定的孔大小和形状，但已知只有不到1%的MOF是灵活的，即它们根据外部刺激改变其孔空间。这使得设计的材料可以对包括温度、压力、光和分子客体在内的各种刺激做出反应，从而允许更精细地控制MOF应用的核心的分子捕获性能。该项目建立在我们最近发现的一种新的灵活的“呼吸”MOF Me2NH2[In(NH2 BDC)2](SHF-61)(NH2 BDC=氨基苯二甲酸酯)的基础上，它表现出显著的客体响应孔洞打开和关闭行为。MOF表现出良好的CO2/N2和CO2/CH4吸附选择性，显示出工业上相关气体分离的潜力，并对不同的小分子客体具有明显不同的灵活响应，这表明潜在的主-客体行为可用于许多分离、检测或催化应用。进一步使这种MOF有别于大多数其他柔性MOF的是，它在动态行为中保持了单晶的完整性，为通过单晶X射线衍射准确和详细地表征结构提供了几乎前所未有的机会。该项目将利用这一非同寻常的机会，深入了解客人响应的灵活行为，作为开发响应材料的平台。我们将通过化学修饰和网状合成(孔空间扩张)来开发一种新的材料家族。将对这些材料进行系统的研究，以提供适用于MOF领域的广泛的基本知识，并在短期内用于包括气体分离在内的选择性分子识别，但也为在催化和其他领域的长期应用奠定基础。这项研究将由一个由化学家和化学工程师组成的多学科团队进行。Brammer-Düren-Fletcher-Oswald团队在MOF的合成、表征和计算建模/模拟方面提供了广泛的经验和必要的专业知识，并建立了合作记录。在卓越的实验室设施的支持下，加上与国家设施的广泛接触，专业的专业知识将使系统和定量的调查成为可能，从而开发出一系列多种多样的MOF材料，并成为全世界研究灵活MOF的基本信息来源。

Metal-organic frameworks (MOFs) are periodic crystalline materials with molecular-scale pores that are among the most widely studied classes of materials across a range of scientific and engineering disciplines. Their modular construction from metal-ion-containing nodes linked by organic ligands enables both spatial and chemical tuning to selectively trap molecules in the pore space. These features allow the performance of MOFs to be optimised for numerous applications including storage and separation of gases, detection of molecules, environmental remediation, catalysis and drug delivery. Their potential impact therefore spans the energy, transport, environmental and health care sectors.The periodic crystalline nature of MOFs makes them amenable to atomic-level characterisation by diffraction methods and extensive characterisation by a variety of spectroscopic techniques, which collectively provide far greater detail pertinent to materials design and optimisation than for non-crystalline competitor materials such as activated carbons. MOFs also present advantages over established crystalline porous materials such as zeolites and similar oxide materials as the modular construction of MOFs from metal ions and organic ligands and the opportunity for post-synthesis chemical modification enables almost limitless versatility in pore size, pore shape and spatial arrangement of chemical functionality. Some 10s of thousands of MOFs have been reported in the past 20 years. Most MOFs have fixed pore sizes and shape, but less than 1% are known to be flexible i.e. they change their pore space in response to an external stimulus. This allows the design of materials that can respond to a variety of such stimuli, including temperature, pressure, light and molecular guests, allowing finer control of molecular capture properties at the heart of applications of MOFs.This project builds on our recent discovery of a new flexible 'breathing' MOF Me2NH2[In(NH2BDC)2] (SHF-61) (NH2BDC = aminobenzenedicarboxylate), which exhibits a substantial guest-responsive pore opening and closing behaviour. The MOF exhibits excellent CO2/N2 and CO2/CH4 adsorption selectivity, indicating potential for industrially relevant gas separation, and has markedly different flexible responses to different small molecule guests, which suggests an underlying host-guest behaviour that can be exploited for many applications in separations, detection or catalysis. What further sets this MOF apart, even from most other flexible MOFs, is that it retains its integrity as single crystals during dynamic behaviour, providing an almost unprecedented opportunity for accurate and detailed structural characterisation by single-crystal X-ray diffraction. This project will exploit this extraordinary opportunity for insight into guest-responsive flexible behaviour as a platform for development of responsive materials. We will develop a new family of materials by chemical modification and reticular synthesis (pore-space expansion). These materials will be studied systematically to provide a broad range a fundamental knowledge applicable to the MOF field, and exploited in the short-term for selective molecular recognition including gas separation, but also to build a foundation for longer-term applications in catalysis and other areas. The research will be conducted by a multi-disciplinary team of chemists and chemical engineers. The Brammer-Düren-Fletcher-Oswald team provide extensive experience and the necessary expertise in synthesis, characterisation and computational modelling/simulation of MOFs and an established record of collaboration. Specialised expertise supported by excellent laboratory facilities and complemented by extensive engagement with national facilities will enable a systematic and quantitative investigation leading to development of a versatile family of MOF materials and a source of fundamental information for research worldwide on flexible MOFs.