Crystal structure of a new polar borate Na₂Ce₂[BO₂(OH)][BO₃]₂ · H₂O with isolated boron triangles

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• 作者：A. P. Topnikova ; E. L. Belokoneva ; O. V. Dimitrova ; A. S. Volkov
• 刊名：Crystallography Reports
• 出版年：2016
• 出版时间：November 2016
• 年：2016
• 卷：61
• 期：6
• 页码：940-944
• 全文大小：634 KB
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Crystallography
  Russian Library of Science
  
• 出版者：MAIK Nauka/Interperiodica distributed exclusively by Springer Science+Business Media LLC.
• ISSN：1562-689X
• 卷排序：61

文摘

Crystals of a new polar borate Na₂Ce₂[BO₂(OH)][BO₃]₂ · H₂O were prepared by hydrothermal synthesis. The crystals are orthorhombic, a = 7.2295(7) Å, b = 11.2523(8) Å, c = 5.1285(6) Å, Z = 2, sp. gr. C2mm (Amm2), R = 0.0253. The formula of the compound was derived from the structure determination. The Ce and Na atoms are coordinated by nine and six O atoms, respectively. The Ce position is split, and a small amount of Ce is incorporated into the Na1 site with the isomorphous substitution for Na. The anionic moieties exist as isolated BO₃ and BO₂(OH) triangles. The planes of the BO₂(OH) triangles with mm2 symmetry are parallel to the ab plane. The planes of the BO₃ triangles with m symmetry are perpendicular to the ab plane and are rotated in a diagonal way. The splitting of the Ce positions and the polar arrangement of the BO₂(OH) triangles, water molecules, and Na atoms are observed along the polar a axis. The new structure is most similar to the new borate NaCa₄[BO₃]₃ (sp. gr. Ama2), in which triangles of one type are arranged in a polar fashion along the c axis. Weak nonlinear-optical properties of both polar borates are attributed to the quenching of the second-harmonic generation due to the mutually opposite orientation of two-thirds of B triangles in the unit cell.