Rajh Tijana, Masson Eric, Latt Kyaw Zin, Smith Ashton, Brugh Alexander M, Dandu Naveen, Trainer Daniel, Curtiss Larry A, Ngo Anh T, Hla Saw-Wai
Nanoscience and Technology Division, Argonne National Laboratory, 9700 S Cass Ave, Argonne, Illinois 60540, United States.
School of Molecular Sciences, Arizona State University, 551 E University Dr, Tempe, Arizona 85281, United States.
Inorg Chem. 2023 Aug 14;62(32):12721-12729. doi: 10.1021/acs.inorgchem.3c01154. Epub 2023 Jul 28.
Variable temperature electron paramagnetic resonance (VT-EPR) was used to investigate the role of the environment and oxidation states of several coordinated Eu compounds. We find that while Eu(III) chelating complexes are diamagnetic, simple chemical reduction results in the formation of paramagnetic species. In agreement with the distorted symmetry of Eu molecular complexes investigated in this study, the EPR spectrum of reduced complexes showed axially symmetric signals ( = 2.001 and = 1.994) that were successfully simulated with two Eu isotopes with nuclear spin 5/2 (Eu and Eu with 48% and 52% natural abundance, respectively) and nuclear -factors Eu/Eu = 2.27. Illumination of water-soluble complex Eu(dipic) at 4 K led to the ligand-to-metal charge transfer (LMCT) that resulted in the formation of Eu(II) in a rhombic environment ( = 2.006, = 1.995, = 1.988). The existence of LMCT affects the luminescence of Eu(dipic), and pre-reduction of the complex to Eu(II)(dipic) reversibly reduces red luminescence with the appearance of a weak CT blue luminescence. Furthermore, encapsulation of a large portion of the dipic ligand with Cucurbit[7]uril, a pumpkin-shaped macrocycle, inhibited ligand-to-metal charge transfer, preventing the formation of Eu(II) upon illumination.
变温电子顺磁共振（VT-EPR）被用于研究几种配位铕化合物的环境和氧化态的作用。我们发现，虽然铕（III）螯合配合物是抗磁性的，但简单的化学还原会导致顺磁性物种的形成。与本研究中所研究的铕分子配合物的扭曲对称性一致，还原配合物的电子顺磁共振谱显示出轴对称信号（g∥ = 2.001和g⊥ = 1.994），用两种核自旋为5/2的铕同位素（分别为天然丰度48%的151Eu和52%的153Eu）以及核g因子g151Eu/g153Eu = 2.27成功模拟。在4K下对水溶性配合物Eu(dipic)进行光照导致配体到金属的电荷转移（LMCT），从而在菱形环境中形成Eu(II)（g∥ = 2.006，g⊥ = 1.995，g⊥ = 1.988）。LMCT的存在影响Eu(dipic)的发光，并且将配合物预还原为Eu(II)(dipic)会可逆地降低红色发光，并出现微弱的电荷转移蓝色发光。此外，用南瓜形大环葫芦[7]脲将大部分dipic配体封装，抑制了配体到金属的电荷转移，防止光照时形成Eu(II)。
