Summers Thomas J, Sobrinho Josiane A, de Bettencourt-Dias Ana, Kelly Shelly D, Fulton John L, Cantu David C
Department of Chemical and Materials Engineering, University of Nevada, Reno, Reno, Nevada 89557-0388, United States.
Department of Chemistry, University of Nevada, Reno, Reno, Nevada 89557-0705, United States.
Inorg Chem. 2023 Apr 3;62(13):5207-5218. doi: 10.1021/acs.inorgchem.3c00199. Epub 2023 Mar 20.
Lanthanide-ligand complexes are key components of technological applications, and their properties depend on their structures in the solution phase, which are challenging to resolve experimentally or computationally. The coordination structure of the Eu ion in different coordination environments in acetonitrile is examined using ab initio molecular dynamics (AIMD) simulations and extended X-ray absorption fine structure (EXAFS) spectroscopy. AIMD simulations are conducted for the solvated Eu ion in acetonitrile, both with or without a terpyridyl ligand, and in the presence of either triflate or nitrate counterions. EXAFS spectra are calculated directly from AIMD simulations and then compared to experimentally measured EXAFS spectra. In acetonitrile solution, both nitrate and triflate anions are shown to coordinate directly to the Eu ion forming either ten- or eight-coordinate solvent complexes where the counterions are binding as bidentate or monodentate structures, respectively. Coordination of a terpyridyl ligand to the Eu ion limits the available binding sites for the solvent and anions. In certain cases, the terpyridyl ligand excludes any solvent binding and limits the number of coordinated anions. The solution structure of the Eu-terpyridyl complex with nitrate counterions is shown to have a similar arrangement of Eu coordinating molecules as the crystal structure. This study illustrates how a combination of AIMD and EXAFS can be used to determine how ligands, solvent, and counterions coordinate with the lanthanide ions in solution.
镧系元素-配体配合物是技术应用的关键组成部分，其性质取决于它们在溶液相中的结构，而通过实验或计算来解析这些结构具有挑战性。使用从头算分子动力学（AIMD）模拟和扩展X射线吸收精细结构（EXAFS）光谱研究了乙腈中不同配位环境下铕离子的配位结构。对乙腈中溶剂化的铕离子进行了AIMD模拟，模拟中有无三联吡啶配体，以及存在三氟甲磺酸盐或硝酸盐抗衡离子的情况。EXAFS光谱直接从AIMD模拟中计算得出，然后与实验测量的EXAFS光谱进行比较。在乙腈溶液中，硝酸盐和三氟甲磺酸盐阴离子均显示直接与铕离子配位，形成十配位或八配位的溶剂配合物，其中抗衡离子分别以双齿或单齿结构结合。三联吡啶配体与铕离子的配位限制了溶剂和阴离子的可用结合位点。在某些情况下，三联吡啶配体排除了任何溶剂结合并限制了配位阴离子的数量。具有硝酸盐抗衡离子的铕-三联吡啶配合物的溶液结构显示出与晶体结构中铕配位分子的类似排列。这项研究说明了如何结合使用AIMD和EXAFS来确定配体、溶剂和抗衡离子在溶液中如何与镧系离子配位。
