水合铀酰与尿嘧啶及其异构体配位体系的计算研究

运用B3LYP/6-311++G**(RLC ECP)方法研究[UO_2(Uracil)j(H_2O)k]~(2+)(Uijk,i为尿嘧啶6种异构体代号,j+k=5)配位体系的几何结构、振动光谱、结合能等性质,并用极化连续介质模型(PCM)考察了溶剂化效应。结果表明,在U1jk体系中,随着尿嘧啶配体数目的逐渐增加,U-Ouracil配位键和U=O键的键长逐渐伸长,水溶液中U=O键的伸缩振动频率逐渐减小,配离子的总结合能呈增加趋势,且气相中的线性拟合效果较好。在Ui14体系中,U-Ouracil的键长与U-OH_2的键长整体成负相关,与U=O键的伸缩振动频率成正相关,结合能最大的配离子并不是由能量最低的尿嘧啶异构体生成的。电子密度拓扑分析表明U-Ouracil键和U-OH_2键具有离子键性质。原子电荷分析揭示在配位过程中是由配体片段向铀酰发生了电子转移,且尿嘧啶的电荷转移量与该配体数目成负相关,其中Ur6异构体向铀酰离子转移电子数最多。

Computational Study on the Coordination Systems of Hydrated Uranyl with Uracil Tautomers

The geometric structure, vibrational spectra and binding energies of[UO₂(Uracil)_j(H₂O)_k]²⁺ (Uijk, i represents six kinds of uracil tautomers and j+k=5) have been studied by B3LYP method with 6-311++G(d, p) and RLC ECP basis sets. The solvent effect of water was simulated by polarized continuum model. The results show that as the number of the uracil increases, the U-O_uracil bond and the U=O bond in coordination ions are elongated and the stretching vibrational frequencies of the U=O bond gradually decrease in the aqueous solution. Meanwhile, the total binding energies of the coordination ions obviously increase, and the calculation also shows a linear relationship between the binding energies and the number of uracil ligand. Besides, the affinity of uracil ligand for the uranyl ion far exceeds that of H₂O ligand. The U-O_uracil bond lengths calculated in the gaseous phase are slightly shorter than those obtained in the aqueous phase, however, the lengths of the U-OH₂ bond show opposite behavior. In the Ui14 system, the bond length of U-O_uracil is negatively correlated with the bond length of U-OH₂, while is positively correlated with the vibrational frequency of U=O bond. The maximum binding energy of the coordination ion is evidently not formed by the lowest energy conformer of uracil. The topological analysis of electron density indicates that the coordination bond shows ionic character. Atomic charge analysis reveals that the charge transfer is from uracil to uranyl during the coordination process, and the amount of the uracil charge is inversely related with coordination number. The Ur6 tautomer possesses the most charge among six kinds of uracil tautomers because of forming bidentate complexation with uranyl.