Three-Dimensional Reference Interaction Site Model Self-Consistent Field Study on the Coordination Structure and Excitation Spectra of Cu(II)-Water Complexes in Aqueous Solution
Three-Dimensional Reference Interaction Site Model Self-Consistent Field Study on the Coordination Structure and Excitation Spectra of Cu(II)-Water Complexes in Aqueous Solution
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水溶液中Cu(II)-水配合物的三维参考相互作用位点模型自洽场研究
DOI：
10.1021/acs.jpca.9b01364
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Nakano Haruyuki
中科院分区：
文献类型：
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作者：
Yang Chen;Watanabe Yoshihiro;Yoshida Norio;Nakano Haruyuki
用Kohn-Sham密度泛函理论(DFT)和三维参考作用点模型(3D-RISM)自洽场方法研究了水合Cu2+离子的分子结构和溶剂化结构及其激发光谱。在水溶液中发现了五种稳定的几何结构：扭曲的八面体[Cu(H2O)6]2+在Ci和D2h对称，方形锥体和三角双锥体[Cu(H2O)5]2+，正方形平面[Cu(H2O)4]2+。在[Cu(H_2O)_6]~(2+)中，扭曲的八面体结构优先于[Cu(H_2O)_6]~(2+)，而正方锥体和三角双锥体的稳定性几乎相同。在这些几何构型中，顺对称的六配位配合物[Cu(H2O)6]2+具有最低的亥姆霍兹能量。[Cu(H2O)6]2+具有扭曲的八面体结构，即两个长轴向键和四个赤道短键。[Cu(H2O)5]2+和[Cu(H2O)4]2+的空间分布函数和径向分布函数分析表明，[Cu(H2O)5]2+和[Cu(H2O)4]2+分别含有1个和2个溶剂水分子，构成了配位体水分分布的扭曲八面体。由分布函数得到的配位数(CNS)分别为5.2-5.4和5.3。这些结果表明，水溶液中的Cu2+离子在第一水化壳层中有5-6个配位水分子，一些不同CNS的结构可能在溶液中互换。利用三维棱镜产生的电场，用含时密度泛函理论计算了低能级d-d激发态的激发能和电子组态。由于所有结构的高度对称性，轨道能量和电子构型与经典晶场理论相似。在[Cu(H_2O)_6]~(2+)中，轨道简并被分解，而在[Cu(H_2O)_5]~(2+)和[Cu(H_2O)_4]~(2+)中，存在弱和强的准简并。结果表明，只有四配位络合物产生了第三和第四激发态，而在其他络合物中没有明显的简并特征。计算得到的激发能与吸收光谱符合得很好。
The molecular and solvation structures of the hydrated Cu2+ions and their excitation spectra were investigated using the Kohn–Sham density functional theory (DFT) and the three-dimensional reference interaction site model (3D-RISM) self-consistent field method. Five stable geometrical structures were found to exist in aqueous solution: the distorted octahedral [Cu(H2O)6]2+inCiandD2hsymmetries, the square pyramidal and trigonal bipyramidal [Cu(H2O)5]2+, and the square planar [Cu(H2O)4]2+. The distorted octahedral structure in theCisymmetry is preferred in [Cu(H2O)6]2+, and the square pyramidal and trigonal bipyramidal [Cu(H2O)5]2+show almost the same stability. Among these geometries, the six-coordinate complex [Cu(H2O)6]2+in theCisymmetry had the lowest Helmholtz energy. [Cu(H2O)6]2+had a distorted octahedral structure, that is, two long axial bonds and four short equatorial bonds. The spatial and radial distribution function analyses for [Cu(H2O)5]2+and [Cu(H2O)4]2+showed that [Cu(H2O)5]2+and [Cu(H2O)4]2+had one and two solvent water molecules that constituted a distorted octahedron with ligand water distribution. The coordination numbers (CNs) derived from the distribution functions were 5.2–5.4 for [Cu(H2O)5]2+and 5.3 for [Cu(H2O)4]2+. These results indicated that the Cu2+ion in an aqueous solution had 5–6 coordination water molecules in the first hydration shell and some structures with different CNs may interchange in the solution. The excitation energies and electronic configurations of low-lying d–d excited states were calculated using the time-dependent DFT with the electric field generated by 3D-RISM. The orbital energies and electronic configurations were in a similar picture to those of the classical crystal field theory because of the highly symmetrical features of all structures. In [Cu(H2O)6]2+, the degeneracies of orbitals were resolved, whereas in [Cu(H2O)5]2+and [Cu(H2O)4]2+, weak and strong quasi-degeneracies remained. As a result, only the four-coordinate complex generated third and fourth excited states, whereas in other complexes, there were no obvious characters of degeneracies. The resulting excitation energies were in good agreement with the absorption spectra.