Abstract A comparative experimental (UV–vis) and theoretical (DFT) study on the nonlinear optical (NLO) response of the double salts Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2 is presented in the current paper. For that purpose, a detailed analysis on the electronic absorption behavior of the compounds under investigation in the range from 200 to 1100 nm is conducted. The position of the experimentally registered electronic transitions is compared with that of the corresponding theoretical ones (calculated by means of DFT at B3LYP/6–311+G(d,p) level of theory). A time-dependent variant of DFT is applied to calculate the oscillator strengths and absorption maxima. Moreover, structural parameters, net atomic charges and molecular electrostatic potential surface are accomplished at B3LYP/6–311+G(d,p) level of theory as well. Results showed that the NLO response depends strongly on the structural water presence. Hence, the ionic salt Cs2Ni(SeO4)2•4H2O is a good NLO material in the middle ultraviolet (MUV), near ultraviolet (NUV) and near infrared (NIR) regions, while MUV and NUV areas characterize Cs2Ni(SeO4)2. However, it was revealed that Cs2Ni(SeO4)2 possesses considerably better NLO properties within 200–400 nm than Cs2Ni(SeO4)2•4H2O. These findings were related to a different electron density rearrangement in the Cs2Ni(SeO4)2•4H2O and Cs2Ni(SeO4)2, a consequence of the metal-oxygen interactions strength.

中文翻译：

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NLO 响应作为结构水存在的函数：Cs2Ni(SeO4)2.4H2O 和 Cs2Ni(SeO4)2 的比较实验 (UV-vis) 和 DFT（结构，NPA，MEP）研究

摘要 本文介绍了 Cs2Ni(SeO4)2•4H2O 和 Cs2Ni(SeO4)2 复盐的非线性光学 (NLO) 响应的对比实验 (UV-vis) 和理论 (DFT) 研究。为此，对所研究化合物在 200 至 1100 nm 范围内的电子吸收行为进行了详细分析。将实验记录的电子跃迁的位置与相应的理论跃迁的位置进行比较（通过 B3LYP/6–311+G(d,p) 理论水平的 DFT 计算）。应用 DFT 的时间相关变体来计算振荡器强度和吸收最大值。此外，结构参数、净原子电荷和分子静电势面也在 B3LYP/6-311+G(d,p) 理论水平上完成。结果表明 NLO 响应在很大程度上取决于结构水的存在。因此，离子盐 Cs2Ni(SeO4)2•4H2O 在中紫外 (MUV)、近紫外 (NUV) 和近红外 (NIR) 区域是一种很好的 NLO 材料，而 MUV 和 NUV 区域则表征 Cs2Ni(SeO4)2。然而，研究表明 Cs2Ni(SeO4)2 在 200-400 nm 范围内具有比 Cs2Ni(SeO4)2•4H2O 更好的 NLO 特性。这些发现与 Cs2Ni(SeO4)2•4H2O 和 Cs2Ni(SeO4)2 中不同的电子密度重排有关，这是金属-氧相互作用强度的结果。结果表明，与 Cs2Ni(SeO4)2•4H2O 相比，Cs2Ni(SeO4)2 在 200-400 nm 范围内具有明显更好的 NLO 特性。这些发现与 Cs2Ni(SeO4)2•4H2O 和 Cs2Ni(SeO4)2 中不同的电子密度重排有关，这是金属-氧相互作用强度的结果。结果表明，与 Cs2Ni(SeO4)2•4H2O 相比，Cs2Ni(SeO4)2 在 200-400 nm 范围内具有明显更好的 NLO 特性。这些发现与 Cs2Ni(SeO4)2•4H2O 和 Cs2Ni(SeO4)2 中不同的电子密度重排有关，这是金属-氧相互作用强度的结果。