Exploration of Al-based metal-organic frameworks with multiple linkers and functionalities - microscopic structuring and proton conduction

金属有机骨架代表了一类用途广泛的多孔材料，其性质可以通过改变骨架拓扑结构、有机连接物分子和引入客体分子来控制。铝结合了Al-MOF的轻质、易得和低毒，以及高的热稳定性和化学稳定性，是构建此类材料最具吸引力的离子之一。然而，其导致微晶材料的倾向往往阻碍结构-性质关系的确定。本项目旨在探索在水和非水合成条件下基于聚羧酸连接物、其官能化衍生物及其混合物的铝基MOF。特别是，通过改变羧酸基团的数量和排列，我们预计将鼓励形成具有新的无机建筑单元和框架的MOF。将特别强调引入自由、酸性质子基团，以创建可能易于质子传导的材料。两性客体分子的加入将有助于建立有效的质子传导途径。为了更好地理解质子施主密度、所结合的客体分子以及颗粒尺寸对质子运动和输运的影响之间的复杂相互作用，本项目将系统地研究骨架、客体和质子本身的动力学过程。为此，我们召集了N.Stock和J.Senker的研究小组，在合成和表征Al-MOF的结构和动力学性质方面增加了他们互补的技能。为了对新的MOF拓扑进行全面和高效的合成筛选，Stock集团将开发两个高通量反应器，使其能够在温度梯度下工作，并进行汽相结晶反应。对于选定的体系，将制定针对颗粒尺寸可控的Al-MOF纳米颗粒的合成策略。为了阐明结构，包括同构MOF中的有序参数和主客体连接性，Senker基团将依赖于结合固体核磁共振光谱和粉末衍射的核磁共振结晶学方法。此外，固体核磁共振波谱将在广泛的温度和频率范围内分析连接基、客体和酸性质子的局部动力学过程中发挥重要作用。为了区分MOF纳米粒子的外表面和内表面的质子迁移率，将使用超极化技术。核磁共振数据应由与教授密切合作进行的与温度相关的阻抗谱研究提供支持。雅内克、帕帕斯塔夫鲁和沃克。对于大多数材料，我们将依赖于直流电导率的行为，并通过基于选定系统的等效电路的交流电导率模拟来补充这些数据。

Metal-organic frameworks represent a versatile class of porous materials, whose properties can be controlled by varying the framework topology, the organic linker molecules and by introducing guest molecules. Aluminium, which combines low weight, easy availability and low toxicity together with a high thermal and chemical stability of the Al-MOFs, is one of the most appealing ions to build such materials. Its tendency to lead to microcrystalline materials, however, often hamper the determination of structure-property relationships. This project aims at exploring Al-based MOFs based on polycarboxylate linkers, their functionalised derivatives and mixtures thereof in both aqueous and non-aqueous synthesis conditions. In particular, by varying number and arrangement of carboxylic acid groups, we expect to encourage the formation of MOFs with new inorganic building units and frameworks. Special emphasis will be placed on introducing free, acidic proton bearing groups to create materials potentially prone to proton conduction. The incorporation of amphoteric guest molecules shall help to establish efficient proton conduction pathways. To develop a better understanding for the complex interplay between the proton donor density, the incorporated guest molecules and the influence of the particle size on the proton mobility and transport, dynamical processes of framework, guests and the protons themselves will be studied systematically within this project.To accomplish this, we brought together the research groups of N. Stock and J. Senker, adding their complementary skills in synthesis and characterisation of structural and dynamical properties of Al-MOFs. For a thorough and efficient synthetic screening of new MOF topologies, the Stock group will develop two high-throughput reactors allowing to work with temperature gradients and to carry out vapour phase crystallisation reactions. For selected systems, synthetic strategies towards Al-MOF nanoparticles with controlled particle sizes will be established. For the structure elucidation, including order parameters in isomorphous MOFs and host-guest connectivities, the Senker group will rely on NMR-crystallographic approaches combining solid-state NMR spectroscopy and powder diffraction. Furthermore, solid-state NMR spectroscopy will play an essential role for analysing local dynamical processes of linkers, guests and acidic protons over a broad temperature and frequency range. To discriminate between proton mobility at the outer vs. the inner particle surfaces of the MOF nanoparticles, hyperpolarisation techniques will be used. The NMR data shall be supported by temperature dependent impedance spectroscopic investigations which will be carried out in close cooperation with Profs. Janek, Papastavrou and Wark. For most materials we will rely on the behaviour of the DC conductivity and complement these data with simulations of the AC conductivity based on equivalent circuits for selected systems.