Nano-Science Center & Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 København Ø, Denmark.
Inorg Chem. 2020 Aug 3;59(15):10409-10421. doi: 10.1021/acs.inorgchem.0c00056. Epub 2020 Feb 28.
The structure of lanthanide(III) ions in solutions high in nitrate has been debated since the early days of lanthanide coordination chemistry. The structure and properties of lanthanides in these solutions are essential in industrial rare-earth separation, as well as in the fundamental solution chemistry of these elements. Pending decades of debate, it was established that nitrate is bidentate and coordinates in the inner sphere, and complexes have been observed with as many as four nitrates coordinated to a single lanthanide(III) center in nonaqueous solutions. We revisit the interactions between nitrate and europium(III) in methanol using optical spectroscopy, X-ray total scattering, and the current understanding of europium(III) photophysics. By a combination of direct and indirect methods to probe the structure, it was found that four distinct species from Eu(MeOH) to [Eu(MeOH)(NO)] are present in solutions containing from 0 to 2 M NO ions. It was shown that the changes in transition probabilities together with high-resolution spectra can provide information on speciation and how the minute changes in ligand field affect the microstates. By a comparison to total X-ray scattering, it was concluded that the optical spectra alone allow the constitution and symmetry of the europium(III) species to be determined. Most notably, the minute changes in the all oxygen atom coordination imply significant changes in the optical properties of the europium(III) center.
自镧系配位化学早期以来，人们就一直在争论高硝酸盐溶液中镧系（III）离子的结构。这些溶液中镧系元素的结构和性质对于工业稀土分离以及这些元素的基础溶液化学都至关重要。经过几十年的争论，已经确定硝酸盐是双齿配体，并在内球中配位，并且已经观察到多达四个硝酸盐与单个镧系（III）中心配位的非水相溶液中的络合物。我们使用光学光谱，X 射线总散射以及当前对铕（III）光物理的了解，重新研究了甲醇中硝酸盐与铕（III）之间的相互作用。通过直接和间接方法的组合来探测结构，发现在从 0 到 2 M 的 NO 离子存在的溶液中存在四种不同的物种，从 Eu(MeOH) 到 [Eu(MeOH)(NO)]。结果表明，跃迁概率的变化以及高分辨率光谱可以提供有关形态和配体场的微小变化如何影响微观状态的信息。通过与总 X 射线散射的比较，可以得出结论，仅光学光谱就可以确定铕（III）物种的组成和对称性。值得注意的是，所有氧原子配位的微小变化意味着铕（III）中心的光学性质发生了重大变化。
