Reddy Th Dhileep N, Ivanov Alexander S, Driscoll Darren M, Jansone-Popova Santa, Jiang De-En
Department of Chemistry, University of California, Riverside, California 92521, United States.
Chemical Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, Tennessee 37831, United States.
ACS Omega. 2022 Jun 9;7(24):21317-21324. doi: 10.1021/acsomega.2c02531. eCollection 2022 Jun 21.
Rare-earth elements (REEs) such as neodymium are critical materials needed in many important technologies, and rigid neutral bis-lactam-1,10-phenanthroline (BLPhen) ligands show one of the highest extraction performance for complexing Nd(III) in REE uptake and separation processes. However, the local structure of the complexes formed between BLPhen and Nd(III) in a typical organic solvent such as dichloroethane (DCE) is unclear. Here, we perform first-principles molecular dynamics (FPMD) simulations to unveil the structure of complexes formed by BLPhen with Nd(NO) in the DCE solvent. BLPhen can bind to Nd(III) in either 1:1 or 2:1 fashion. In the 1:1 complex, three nitrates bind to Nd(III) via the bidentate mode in the first solvation shell, leading to the formation of a neutral complex, [Nd(BLPhen)(NO)], in the organic phase. In contrast, there are two nitrates in the first solvation shell in the 2:1 complex, creating a charged complex, [Nd(BLPhen)(NO)]. The third nitrate was found to be far away from the metal center, migrating to the outer solvation shell. Our simulations show that the binding pocket formed by the two rigid BLPhen ligands allows ample space for two nitrates to bind to the Nd(III) center from opposite sides. Our findings of two nitrates in the first solvation shell of the 2:1 complex and the corresponding bond distances agree well with the available crystal structure. This study represents the first accurate FPMD modeling of the BLPhen-Nd(III) complexes in an explicit organic solvent and opens the door to more atomistic understanding of REE separations from first principles.
钕等稀土元素是许多重要技术所需的关键材料，刚性中性双内酰胺-1,10-菲咯啉（BLPhen）配体在稀土元素吸收和分离过程中对Nd(III)的络合表现出最高的萃取性能之一。然而，在典型的有机溶剂如二氯乙烷（DCE）中，BLPhen与Nd(III)形成的配合物的局部结构尚不清楚。在此，我们进行第一性原理分子动力学（FPMD）模拟，以揭示BLPhen与Nd(NO)在DCE溶剂中形成的配合物的结构。BLPhen可以以1:1或2:1的方式与Nd(III)结合。在1:1配合物中，三个硝酸盐在第一溶剂化层中通过双齿模式与Nd(III)结合，导致在有机相中形成中性配合物[Nd(BLPhen)(NO)]。相比之下，在2:1配合物的第一溶剂化层中有两个硝酸盐，形成带电荷的配合物[Nd(BLPhen)(NO)]。发现第三个硝酸盐远离金属中心，迁移到外部溶剂化层。我们的模拟表明，由两个刚性BLPhen配体形成的结合口袋为两个硝酸盐从相反侧与Nd(III)中心结合提供了足够的空间。我们在2:1配合物的第一溶剂化层中发现两个硝酸盐以及相应键长的结果与现有的晶体结构非常吻合。这项研究代表了在明确的有机溶剂中对BLPhen-Nd(III)配合物的首次精确FPMD建模，并为从第一原理更深入地理解稀土元素分离打开了大门。
