Max Planck Institute for Chemical Energy Conversion (CEC), Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany.
Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 5-7, 45141 Essen, Germany.
Inorg Chem. 2022 Jul 25;61(29):11173-11181. doi: 10.1021/acs.inorgchem.2c01141. Epub 2022 Jul 14.
The recent successes in the isolation and characterization of several bismuth radicals inspire the development of new spectroscopic approaches for the in-depth analysis of their electronic structure. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for the characterization of main group radicals. However, the large electron-nuclear hyperfine interactions of Bi (Bi, = 9/2) have presented difficult challenges to fully interpret the spectral properties for some of these radicals. Parallel-mode EPR (∥) is almost exclusively employed for the study of > 1/2 systems but becomes feasible for = 1/2 systems with large hyperfine couplings, offering a distinct EPR spectroscopic approach. Herein, we demonstrate the application of conventional X-band parallel-mode EPR for = 1/2, = 9/2 spin systems: Bi-doped crystalline silicon (Si:Bi) and the molecular Bi radicals [L(X)Ga]Bi (X = Cl or I) and [L(Cl)GaBi(cAAC)] (L = HC[MeCN(2,6-PrCH)]). In combination with multifrequency perpendicular-mode EPR (X-, Q-, and W-band frequencies), we were able to fully refine both the anisotropic - and -tensors of these molecular radicals. The parallel-mode EPR experiments demonstrated and discussed here have the potential to enable the characterization of other = 1/2 systems with large hyperfine couplings, which is often challenging by conventional perpendicular-mode EPR techniques. Considerations pertaining to the choice of microwave frequency are discussed for relevant spin-systems.
最近在分离和表征几个铋自由基方面的成功，激发了开发新的光谱方法来深入分析其电子结构。电子顺磁共振（EPR）光谱学是表征主族自由基的有力工具。然而，Bi（Bi，=9/2）的大电子-核超精细相互作用对这些自由基中的一些自由基的光谱性质的完全解释提出了很大的挑战。平行模式 EPR（∥）几乎专门用于研究>1/2 体系，但对于具有较大超精细耦合的=1/2 体系也变得可行，提供了一种独特的 EPR 光谱方法。在此，我们展示了常规 X 波段平行模式 EPR 在=1/2、=9/2 自旋体系中的应用：掺铋晶体硅（Si:Bi）和分子 Bi 自由基[L（X）Ga]Bi（X=Cl 或 I）和[L（Cl）GaBi（cAAC）]（L=HC[MeCN（2,6-PrCH）]）。结合多频垂直模式 EPR（X-、Q-和 W-波段频率），我们能够完全精修这些分子自由基的各向异性-和-tensors。这里演示和讨论的平行模式 EPR 实验有可能使具有大超精细耦合的其他=1/2 体系的表征成为可能，这通常是通过常规垂直模式 EPR 技术来实现的。讨论了与微波频率选择有关的考虑因素，这些因素适用于相关的自旋体系。
