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

• Published in: Crystallography reports 2016-11, Vol.61 (6), p.940-944
• Main Authors: Topnikova, A. P., Belokoneva, E. L., Dimitrova, O. V., Volkov, A. S.
• Format: Article
• Language: English
• Subjects: Atomic structure; Borates; Crystal structure; Crystallography and Scattering Methods; Hydrothermal crystal growth; Molecular structure; Nonlinear optics; Optical properties; Physics; Physics and Astronomy; Second harmonic generation; Structure of Inorganic Compounds; Symmetry; Unit cell
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774516060171

Crystals of a new polar borate Na 2 Ce 2 [BO 2 (OH)][BO 3 ] 2 · H 2 O 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. C 2 mm ( Amm 2), 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 BO 3 and BO 2 (OH) triangles. The planes of the BO 2 (OH) triangles with mm 2 symmetry are parallel to the ab plane. The planes of the BO 3 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 BO 2 (OH) triangles, water molecules, and Na atoms are observed along the polar a axis. The new structure is most similar to the new borate NaCa 4 [BO 3 ] 3 (sp. gr. Ama 2), 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.