Synthesis, Structure, and Properties of the Noncentrosymmetric Hydrated Borate Na2B5O8(OH)∙2H2O.

Single crystal of hydrated sodium borate Na2B5O8(OH)∙2H2O has been grown with sizes up to 5 × 5 × 3 mm3 under mild hydrothermal conditions at 180°C. The structure is determined by single-crystal X-ray diffraction and further characterized by IR and TG analyses. It crystallizes in the orthorhombic space group Pna21, with a =11.967(2) Å, b = 6.5320(13) Å, c = 11.126(2) Å, Z = 4, R1 = 0.0183, and wR2 = 0.0483. The crystal structure of Na2B5O8(OH)∙2H2O is made up of Na—O polyhedra, and [B5O8(OH)]2- polyborate anions. Transmittance spectrum is performed on the Na2B5O8(OH)∙2H2O crystal, which shows an absorption edge less than 190 nm in the UV region. The powder second-harmonic generation intensity measured by Kurtz—Perry method indicates that Na2B5O8(OH)∙2H2O is about half that of KH2PO4(KDP). [ABSTRACT FROM AUTHOR]