Direct determination of spin-spin interactions in transition metal-radical complexes relevant in catalysis and molecular magnetism by high-frequency electron-paramagnetic resonance

金属自由基配合物在（生物）催化中起着决定性的作用，并且作为单分子磁体（SMM）变得越来越重要。因此，非无辜配体大大扩展了过渡金属离子（TMI）催化剂的化学性质，也可以作为底物与金属短暂结合，最突出的是O2/O2·-/O22-等小分子。在含有自由基配体的分子磁体中，强交换耦合已被证明能够有效地抑制弛豫途径，例如磁化或拉曼型过程的量子隧穿。这种配合物的自旋态能量的知识，从而潜在的交换相互作用之间的自旋的金属和配体自由基（S）是必不可少的表征它们的电子结构，结构特性的反应性或弛豫行为，分别。尽管它们针对不同的功能特性进行了优化，但基于金属自由基的催化剂和SMM具有相同的自旋耦合机制。该项目的目的是研究与（生物）催化相关的铁基和钴基金属自由基络合物的自旋结构，重点是氧活化过程，以及通过EPR光谱，特别是频域傅里叶变换（FD-FT）THz-EPR的单分子磁性。这种方法采用了最近的成就，证明这是一个强大的，准确的和灵敏的方法来评估电子交换相互作用的高自旋TMI化合物与多个顺磁中心的最重要的细节。在这样做时，它利用了这样的事实，即在自旋系统中存在显著的各向异性，例如零场分裂或交换各向异性，赠款不同总电子自旋St的自旋耦合态之间的形式禁戒跃迁足够的检测概率。在（生物）催化领域，焦点主要是与双氧活化相关的化合物，例如在开环双加氧酶和CoII-超氧配合物的催化循环中金属自由基中间体的Fe和Co模型。在研究含自由基配体的分子磁体之前，对单核Co II-自由基模型配合物进行了系统的研究，为随后分析自由基桥接的双核Co和Fe SMM奠定了基础。磁态的EPR谱有助于发展稳健的、基于哈密顿的自旋系统描述，从而允许从模拟中精确量化相互作用参数。结果被用来建立自旋性质，结构性质和反应性或弛豫行为，分别在金属自由基配合物的磁结构之间的相关性。

Metal-radical complexes play a decisive role in (bio-)catalysis and become increasingly important as single-molecule magnets (SMMs). So do non-innocent ligands substantially extend the chemistry of transition metal ion (TMI) catalysts, and can also occur as substrates transiently binding to the metal, most prominently small molecules such as O2/O2•-/O22-. In radical ligand-containing molecular magnets, strong exchange couplings have been shown to be able to efficiently suppress relaxation pathways, such as quantum tunneling of the magnetization or Raman-type processes. Knowledge of the spin state energies of such complexes and thus the underlying exchange interactions between the spins of the metal and the ligand radical(s) is essential for characterization of their electronic structure, to relate structural properties to reactivity or relaxation behaviour, respectively. Despite their optimization towards different functional properties, metal-radical based catalysts and SMMs share the same spin coupling mechanisms. Thus, the same efficient methods can be applied for their investigation.The aim of the project is to study the spin structures in Fe- and Co-based metal-radical complexes with relevance to (bio-)catalysis, with a focus on oxygen activation processes, and single-molecule magnetism by EPR spectroscopy, particularly frequency-domain Fourier-transform (FD-FT) THz-EPR. This approach employs recent achievements demonstrating this to be a powerful, accurate and sensitive method to evaluate electron exchange interactions in high-spin TMI compounds with multiple paramagnetic centers in paramount detail. In doing so, it makes use of the fact that the presence of substantial anisotropy in spin systems, e.g. zero-field splitting or exchange anisotropy, grants formally forbidden transitions between spin-coupled states of different total electron spin St sufficient probability for their detection.In the field of (bio-)catalysis, the focus is mainly on compounds relevant for dioxygen activation, such as Fe and Co models for metal-radical intermediates in the catalytic cycles of ring-cleaving dioxygenase enzymes and CoII-superoxo complexes. The investigation of radical ligand-containing molecular magnets is preceded by systematic studies of mononuclear CoII-radical model complexes, which lay the groundwork for the subsequent analysis of radical-bridged dinuclear Co and Fe SMMs. The EPR spectra of magnetic states serve to develop robust, Hamiltonian-based descriptions of the spin systems that allow precise quantification of interaction parameters from simulations. The results are used to establish magneto-structural correlations between spin properties, structural properties and reactivity or relaxation behaviour, respectively, in metal-radical complexes.