CEA, Nuclear Energy Division, Research Department of Mining, and Fuel Recycling Processes, BP 17171, F-30207, Bagnols sur Cèze, France.
A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, 119071, Russia.
Chemistry. 2019 Mar 21;25(17):4435-4451. doi: 10.1002/chem.201805858. Epub 2019 Feb 28.
The magnetic properties of Ln and An complexes formed with dipicolinate ligands have been studied by NMR spectroscopy. To know precisely the geometries of these complexes, a crystallographic study by single-crystal X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) in solution was performed. Several methods to separate the paramagnetic shifts observed in the NMR spectra were applied to these complexes. Methods using a number of nuclei of the dipicolinate ligands revealed an abrupt change in the geometries of the complexes and a metal-ligand interaction in the middle of the lanthanide series. A study of the variation of the paramagnetic shifts with temperature demonstrated that higher-order terms of the dipolar and contact contributions are required, especially for the lightest Ln and almost all the studied An . Bleaney's parameters and relating to the contact and dipolar terms, respectively, were deduced from experimental data and compared with the results of ab initio calculations. Quite a good agreement was found for the temperature dependencies of and . However, the values obtained from cation magnetic anisotropy calculations showed some discrepancies with the values derived from Bleaney's equation defined for Ln . Other parameters, such as the crystal field parameter and the hyperfine constants F obtained from the experimental data of the [An(ethyl-dpa) ] complexes (ethyl-dpa=4-ethyl-2,6-dipicolinic acid), are at odds with the assumptions underlying Bleaney's theory.
镧系和锕系元素与二吡啶甲酸盐配体形成的配合物的磁性通过 NMR 光谱进行了研究。为了精确确定这些配合物的几何形状，通过单晶 X 射线衍射（XRD）和溶液中的扩展 X 射线吸收精细结构（EXAFS）进行了晶体学研究。针对这些配合物，应用了几种分离 NMR 光谱中观察到的顺磁位移的方法。使用二吡啶甲酸盐配体的多个核的方法揭示了配合物几何形状的急剧变化，以及在镧系元素系列中间的金属-配体相互作用。对顺磁位移随温度的变化的研究表明，需要更高阶的偶极子和接触贡献项，特别是对于最轻的镧系元素和几乎所有研究的锕系元素。分别从实验数据推导出了与接触项和偶极项相关的 Bleaney 参数 和 ，并将其与从头算计算的结果进行了比较。对于 和 的温度依赖性，发现了相当好的一致性。然而，从阳离子磁各向异性计算得出的 值与 Bleaney 方程定义的镧系元素的 值存在一些差异。其他参数，如从[An(ethyl-dpa) ]配合物（ethyl-dpa=4-乙基-2,6-二吡啶甲酸）的实验数据得出的晶体场参数和超精细常数 F，与 Bleaney 理论的基本假设不一致。
