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首页> 外文期刊>Crystallography reports >Crystal structure of the lead bromo-borate Pb-2[B5O9]Br from precision single-crystal X-ray diffraction data and the problem of optical nonlinearity of hilgardites
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Crystal structure of the lead bromo-borate Pb-2[B5O9]Br from precision single-crystal X-ray diffraction data and the problem of optical nonlinearity of hilgardites

机译：基于精密单晶X射线衍射数据的溴硼酸铅Pb-2 [B5O9] Br的晶体结构和白云母的光学非线性问题

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摘要

The structural features responsible for the high nonlinear optical activity of crystals of the hilgardite-like anhydrous bromo-borate Pb-2[B5O9]Br (space group Pnn2) are analyzed with the use of data obtained from two (precision and conventional) single-crystal X-ray diffraction experiments. The electron-density peaks associated with the stereochemically active lone electron pair are located in free space at two equally probable positions in the vicinity of the Pb(2) atom on the side of the two most distant atoms, Br(1) and Br(2). The stereochemical activity of two nonequivalent lead atoms in the crystal structure increases upon changing over from the Pb(1) atom to the Pb(2) atom. This is in agreement with the behavior of the lone electron pairs in the hilgardite-like hydrated borate Na0.5Pb2[B5O9](OH)(1.5) center dot 0.5H(2)O and another nonlinear optical borate, namely, Pb-2[B4O5(OH)(4)](OH)(2) center dot H2O, which is related to the compound BiB3O6. The most pronounced nonlinear optical properties of the lead bromo-borate Pb-2[B5O9]Br as compared to other orthorhombic hilgardites and lead borates are associated with the presence of highly polarized Pb-Br bonds. In this case, the electron density of the lone electron pair of the Pb(2) atom enhances the polarization effect.
机译：利用从两个（精密和常规）单晶获得的数据，分析了类硅藻石样无水溴化硼酸盐Pb-2 [B5O9] Br（空间群Pnn2）的晶体的高非线性光学活性的结构特征。晶体X射线衍射实验。与立体化学活性孤电子对相关的电子密度峰位于自由空间中两个最相距较远的原子Br（1）和Br（ 2）。从Pb（1）原子转换为Pb（2）原子时，晶体结构中两个不等价的铅原子的立体化学活性增加。这与白铁矿状水合硼酸盐Na0.5Pb2 [B5O9]（OH）（1.5）中心点0.5H（2）O和另一种非线性光学硼酸盐Pb-2中孤电子对的行为一致[B4O5（OH）（4）]（OH）（2）中心点H2O，与化合物BiB3O6有关。溴硼酸铅Pb-2 [B5O9] Br与其他正交斜长石和硼酸铅相比，最明显的非线性光学性质与高极化Pb-Br键有关。在这种情况下，Pb（2）原子的孤电子对的电子密度增强了极化效应。

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