Department of Physics, Stockholm University, AlbaNova University Centre, 106 91 Stockholm, Sweden.
J Phys Chem A. 2010 Mar 18;114(10):3615-21. doi: 10.1021/jp911271q.
The electronic spectra of uranyl(VI) coordinated with four equatorial halide ligands, [UO2X4]2- (X = F, Cl, Br, and I), have been calculated at the all-electron level using the multiconfigurational CASPT2 method, with spin-orbit coupling included through the variational-perturbational method. The halide-to-uranyl charge-transfer states were taken into account in the calculation by including ligand orbitals in the active space. In order to do that, it is assumed that the charge transfer takes place from only one of the four ligands. Two models, which in principle can describe this, were investigated: the first one makes use of a localizing technique and the second one replaces three ligands by ab initio model potentials (AIMPs). The basis set dependence was investigated by using two different basis sets for the halides, of triple-zeta and quadruple-zeta quality. The localization procedure turned out to be strongly basis set dependent, and the most stable results were obtained with ab initio model potentials. The ground state is a closed shell singlet state, and the first excitation is from the bonding sigma(u) orbital on uranyl to the nonbonding delta(u) orbitals, except for the [UO2I4]2- complex, where the first excited state has a mixed character of charge transfer from the I- and the sigma(u)(1)phi(u)(1) configuration. In [UO2F4]2- there is no charge transfer excitation below 50,000 cm(-1) , while in [UO2Cl4]2- it appears around 33,000 cm(-1) and in [UO2Br4]2- around 23,000 cm(-1) . A blueshift of the spectra, from F- to I-, is observed. The calculations compare reasonably well with available experimental results.
铀酰(VI)与四个赤道卤化物配体[UO2X4]2-（X = F、Cl、Br 和 I）配位的电子光谱已使用多组态 CASPT2 方法在全电子水平上进行了计算，其中自旋轨道耦合通过变分-微扰方法包含在内。卤化物到铀酰的电荷转移态已通过在活性空间中包含配体轨道计入计算中。为了做到这一点，假设电荷转移仅发生在四个配体之一中。研究了两种原则上可以描述这种情况的模型：第一种模型利用局部化技术，第二种模型用从头算模型势（AIMPs）替代三个配体。通过使用两种不同的卤化物基组（三重 zeta 和四重 zeta 质量）研究了基组依赖性。局部化过程强烈依赖于基组，并且使用从头算模型势获得了最稳定的结果。基态是一个闭壳单重态，第一个激发态是从铀酰的成键 sigma(u)轨道到非键 delta(u)轨道，除了[UO2I4]2-络合物，其中第一个激发态具有从 I-和 sigma(u)(1)phi(u)(1)构型转移电荷的混合特征。在[UO2F4]2-中，在 50000cm(-1)以下没有电荷转移激发，而在[UO2Cl4]2-中，它出现在 33000cm(-1)左右，在[UO2Br4]2-中出现在 23000cm(-1)左右。观察到光谱从 F-到 I-的蓝移。计算结果与现有实验结果相当吻合。
