EPR spectroscopy of paramagnetic centers and adsorption complexes in porous metal organic frameworks: Development and application of dielectric resonators and microresonators for investigations of small single crystals

多孔金属有机骨架（MOF）化合物是一类新型材料，在吸附、分离、催化和传感等领域具有广阔的应用前景。许多这些材料含有顺磁性离子作为主要的框架成分。因此，利用EPR光谱详细表征顺磁性离子及其与吸附剂和反应物的相互作用，对于理解MOF材料的吸附和催化性能以及设想其未来的应用至关重要。不幸的是，对于MOF系统的EPR研究仅限于粉末材料，因为单晶只能在亚毫米大小。然而，要对形成的吸附配合物的结构进行适当的解释，在许多情况下，需要了解磁张量相对于晶体轴架的方向，而这只能从单晶实验中推断出来。在这里，我们将使用在第一个资助期开发的具有高介电常数（eps = 80）的介电谐振器来研究选定的小MOF单晶中的顺磁吸附配合物，并确定磁相互作用张量相对于晶体轴框架的方向。使用介电谐振器可以将EPR灵敏度提高一个数量级，并且现在可以在亚毫米MOF单晶上进行EPR测量。此外，我们将开发基于介电谐振器和微谐振器的小型MOF单晶脉冲EPR光谱装置。它们将允许我们通过ESEEM光谱阐明吸附配合物中配体超精细耦合张量的取向，并将提供有关其复杂结构的详细信息。

Porous metal-organic framework (MOF) compounds are a novel class of materials, which offer a large application potential in various areas such as adsorption, separation, catalysis, and sensing. Many of these materials contain paramagnetic ions as major framework constituents. Therefore, a detailed characterization of paramagnetic ions and their interaction with adsorbates and reactants by EPR spectroscopy is of uttermost importance for the the understanding of the adsorptive and catalytic properties and the envisaged future applications of MOF materials. Unfortunately, EPR investigations of MOF systems are restricted to powder materials so far as single crystals are only available in sub-millimeter sizes. However a proper elucidation of the structure of the formed adsorption complexes requires knowledge about the orientation of the magnetic tensors with respect to the crystallographic axes frame in many cases which can only be deduced from single crystal experiments. Here we will use dielectric resonators with high permittivities (eps = 80) that have been developed in the first funding period to study paramagnetic adsorption complexes in selected small MOF single crystals and to determine the orientation of the magnetic interaction tensors with respect to the crystallographic axes frame. The use of dielectric resonators may improve the EPR sensitivity by one order of magnitude and allows EPR measurements on sub-millimeter MOF single crystals now. In addition we will develop set-ups for pulsed EPR spectroscopy of small MOF single crystals that are based on dielectric resonators and micro resonators. They will allow us to elucidate the orientation of the ligand hyperfine coupling tensors in the adsorption complexes by ESEEM spectroscopy and will provide detailed information about their complex structure.