Sun Taoxiang, Xu Chao, Xie Xiaofeng, Chen Jing, Liu Xuegang
Institute of Nuclear and New Energy Technology, Beijing Key Lab of Radioactive Waste Treatment, Collaborative Innovation Center of Advanced Nuclear Energy Technology, Tsinghua University, Beijing 100084, China.
ACS Omega. 2018 Apr 11;3(4):4070-4080. doi: 10.1021/acsomega.8b00359. eCollection 2018 Apr 30.
The extraction of lanthanide series by Cyanex301, i.e., bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301), has been modeled by density functional theory calculation, taking into account the formation of both inner- and outer-sphere complexes. The inner-sphere complex Ln(C301) and the outer-sphere complex Ln(HO)(C301) are optimized, followed by the analysis of interaction energy, bond length, Laplacian bond orders, and Mulliken populations. The covalency degree increases in Ln-S and Ln-O bonds in the inner- and outer-sphere complexes, respectively, as the lanthanide series is traversed. Mulliken population analysis indicates the important role of the 5d-orbital participation in bonding in the formation of inner- and outer-sphere complexes. Two thermodynamic cycles regarding the formation of inner- and outer-sphere complexes are established to calculate the extraction Gibbs free energies (Δ ), and relaxed potential energy surface scan is utilized to model the kinetic complexation of C301 anion with hydrated metal ions. Light lanthanides can form both inner- and outer-sphere complexes, whereas heavy lanthanides only form outer-sphere complexes in biphasic extraction. After adopting the data of forming inner-sphere complex for light Ln(III) and that of forming outer-sphere complexes for heavy Ln(III), the trend of the calculated -Δ agrees very well with that of the experimental distribution ratios on crossing the Ln(III) series. Results from this work help to theoretically understand the extraction behavior of Cyanex301 with respect to different Ln(III).
采用密度泛函理论计算对Cyanex301（即双（2,4,4-三甲基戊基）二硫代次膦酸（HC301））萃取镧系元素进行了模拟，同时考虑了内界和外界配合物的形成。对内界配合物Ln(C301)和外界配合物Ln(HO)(C301)进行了优化，随后分析了相互作用能、键长、拉普拉斯键级和穆利肯布居数。随着镧系元素的递变，内界和外界配合物中Ln-S键和Ln-O键的共价程度分别增加。穆利肯布居数分析表明5d轨道参与内界和外界配合物形成过程中键合的重要作用。建立了两个关于内界和外界配合物形成的热力学循环来计算萃取吉布斯自由能（Δ ），并利用松弛势能面扫描对内界配合物C301阴离子与水合金属离子的动力学络合进行了模拟。轻镧系元素能形成内界和外界配合物，而重镧系元素在双相萃取中仅形成外界配合物。采用轻Ln(III)形成内界配合物的数据和重Ln(III)形成外界配合物的数据后，计算得到的-Δ 趋势与Ln(III)系列中实验分配比的趋势非常吻合。这项工作的结果有助于从理论上理解Cyanex301对不同Ln(III)的萃取行为。
