Monitoring adsorption induced structural transformations of MOFs at a molecular level by in situ EPR spectroscopy

在柔性配位聚合物中，可切换mof是多孔材料的一个子类，具有诸如压力门控、响应性和选择性分子识别等迷人的特性。了解并最终控制闸门开启过程中的这些特性是当今MOF研究的重要目标。响应性柔性mof的一个特别有趣的功能是对气体或液体混合物的选择性吸附。一些开放式问题需要解决在这种背景下的特定属性等气体或液体混合物中负责转换行为(QP4 QF1),有首选adsorp-tion网站活跃组件(QP4),什么是不活跃的组件的影响在浇注过程mix-ture (QF1),不活跃的组件进入毛孔,如果是,是如何分布在孔隙系统(QF1),最后,例如，在由柔性和刚性框架组成的核/壳系统中，介观参数如何调节柔性组件的切换行为（QP3）。如果有合适的准磁探针，连续波（cw）和脉冲电子顺磁共振（EPR）光谱可以在局部分子水平上表征和探索MOF框架的开关和吸附分子的性质。我们将使用位于孔隙中的顺磁框架离子（Cu2+, Mn2+）和氮氧化物自由基（TEMPO）作为局部探针，研究气体和液体混合物（QF1, QF2）在柔性MOF材料DUT-8(Ni) (S2), DUT-128(Ni) （S2）和[M11-xM2x(fu1-bdc ')2-y（fu2-bdc″）yP]n （S1）上吸附的门控过程和选择性分子识别。在混合物的连续波原位EPR吸附实验（QP2）中，顺磁性离子将提供浇注过程引起的桨轮单元框架结构变化的信息，而TEMPO自由基的翻滚运动将作为孔隙打开和关闭的敏感指标（T2）。Cu2+和Mn2+自旋探针还用于研究由可切换和刚性DUT-8(Ni)/DUT-8（Zn）衍生物（S2）组成的介观核/壳体系（QP3）的吸附刺激门控。除了cw EPR之外，HYSCORE和脉冲ENDOR光谱在量子化学计算（T1）的支持下，将使用局部顺磁探针研究二元气体和液体混合物在开关过程中活性和非活性两种组分在孔隙中的分布。

Among flexible coordination polymers switchable MOFs are a subclass of porous materials with fascinating properties such as pressure gating, responsiveness, and selective molecular recogni-tion. The understanding and ultimately the control of these properties in gate opening processes are important objectives in MOF research today. A particular interesting functionality of responsive flex-ible MOFs is the selective adsorption from gaseous or liquid mixtures. A number of open questions needs to be addressed in this context such as what are the specific properties of gases or liquids in a mixture that are responsible for the switching behaviour (QP4, QF1), are there preferred adsorp-tion sites for the active component (QP4), what is the influence of the inactive component in a mix-ture on the gating process (QF1), does the inactive component enter the pores and if yes, how is it distributed across the pore system (QF1), and finally, how do mesoscopic parameters for instance in core/shell systems composed of flexible and rigid frameworks modulate the switching behaviour of the flexible component (QP3). Continuous wave (cw) and pulsed electron paramagnetic reso-nance (EPR) spectroscopy can be used to characterize and explore the switching of the MOF framework and the properties of the adsorbed molecules on a local molecular level if suitable par-amagnetic probes are available. We will employ paramagnetic framework ions (Cu2+, Mn2+) and nitroxide radicals (TEMPO) located in the pores as local probes to investigate gating processes and selective molecular recognition for the adsorption of gaseous and liquid mixtures (QF1, QF2) over the flexible MOF materials DUT-8(Ni) (S2), DUT-128(Ni) (S2), and [M11-xM2x(fu1-bdc′)2-y(fu2-bdc″)yP]n (S1). In cw in situ EPR adsorption experiments of mixtures ( QP2) the paramagnetic ions will provide information about the structural changes of the framework at the paddle wheel units caused by the gating process, whereas the tumbling motion of the TEMPO radicals will serve as a sensitive indicator for the opening and closing of the pores (T2). Cu2+ and Mn2+ spin probes are also used to study the adsorption-stimulated gating for mesoscopic core/shell systems (QP3) composed of switchable and rigid DUT-8(Ni)/DUT-8(Zn) derivatives (S2). Besides cw EPR, HYSCORE and pulsed ENDOR spectroscopy, supported by quantum chemical calculations (T1), will be applied to investigate the distribution of the two components, active and inactive in the switching process, of binary gas and liquid mixtures across the pores using local paramagnetic probes.