Jennifer G Abigail, Schreckenbach Georg, Varathan Elumalai
Department of Chemistry, SRM Institute of Science and Technology, Kattankulathur, Chennai 603203, Tamil Nadu, India.
Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
Dalton Trans. 2024 May 7;53(18):7899-7911. doi: 10.1039/d4dt00395k.
In the process of handling and storage of radioactive actinides it is essential to selectively sequester the minor actinides, such as Am and Cm, through a competitive complexation process. Herein we computationally designed two core modified ligands (L2 and L3) through systematic oxygen substitution at the NH sites of dipyriamethyrin (L1_2H), a hexadentate expanded porphyrin, and studied their competitive complexation towards trivalent actinides (An = Am/Cm) from their trichlorides using density functional theory (DFT). We observed shorter An-N bonds and longer An-O bonds in complexes based on core modified ligands (L2 and L3). The An-Cl bond length increases with increasing axial coordination number (, from L1 to L3) to accommodate the ligands. All the bonds were identified to be electrostatic in nature. L1 exhibits shorter bonds and larger bond orders on complexing with Am than with Cm. On moving from complexes of L2 to L3, the An-N bond lengths are shortened, while An-O bond lengths become larger. Between the complexes of Am and Cm, there is marginal difference in their bond distances with L2 and L3. Charge analysis shows ligand to metal charge transfer during coordination, with back-donation from An to N/O and Cl. The calculated spin-density analysis indicates that An remains in its trivalent oxidation state on complexation, while orbital occupation analysis shows that the 5f and 6d orbitals are involved in bonding; this was confirmed by molecular orbital (MO) analysis that shows the complexes of L2 and L3 to exhibit higher degeneracy in their overlapping MOs. Further, the energy decomposition analysis (EDA) confirms that all ionic bonds are primarily due to electrostatic contributions, where the orbital contributions increase from L1 to L3 complexes and maximum covalency was observed in Cm complexes due to the energy matching between the 5f orbitals of Cm and the 2p orbitals of N and Cl, compared to Am. To confirm the competitiveness in the complexation of the ligand towards Am Cm, the thermodynamic parameters were analysed for the ligand and metal substitution reactions. L1 shows more affinity towards Am than Cm, while L2 and L3 prefer Cm.
在放射性锕系元素的处理和储存过程中，通过竞争性络合过程选择性地隔离次要锕系元素（如镅和锔）至关重要。在此，我们通过在六齿扩展卟啉二吡啶甲基卟啉（L1_2H）的NH位点进行系统的氧取代，通过计算设计了两种核心修饰配体（L2和L3），并使用密度泛函理论（DFT）研究了它们从三氯化物中对三价锕系元素（An = Am/Cm）的竞争性络合。我们观察到基于核心修饰配体（L2和L3）的络合物中An-N键较短，An-O键较长。An-Cl键长度随着轴向配位数的增加（从L1到L3）而增加，以容纳配体。所有键在本质上均被确定为静电键。与Cm络合时相比，L1与Am络合时表现出更短的键和更大的键级。从L2的络合物到L3的络合物，An-N键长度缩短，而An-O键长度变大。在Am和Cm的络合物之间，它们与L2和L3的键距存在微小差异。电荷分析表明配位过程中存在配体到金属的电荷转移，同时存在从An到N/O和Cl的反馈。计算得到的自旋密度分析表明，络合时An保持其三价氧化态，而轨道占据分析表明5f和6d轨道参与成键；分子轨道（MO）分析证实了这一点，该分析表明L2和L3的络合物在其重叠MO中表现出更高的简并度。此外，能量分解分析（EDA）证实所有离子键主要归因于静电贡献，其中轨道贡献从L1到L3络合物增加，并且由于Cm的5f轨道与N和Cl的2p轨道之间的能量匹配，在Cm络合物中观察到最大共价性，与Am相比。为了证实配体对Am Cm络合的竞争性，分析了配体和金属取代反应的热力学参数。L1对Am的亲和力比对Cm的亲和力更强，而L2和L3更倾向于Cm。
