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

Single crystal of hydrated sodium borate Na(2)B(5)O(8)(OH).2H(2)O has been grown with sizes up to 5 x 5 x 3 mm(3) under mild hydrothermal conditions at 180 degrees 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 Pna2(1), with a = 11.967(2) A, b = 6.5320(13) A, c = 11.126(2) A, Z = 4, R1 = 0.0183, and wR2 = 0.0483. The crystal structure of Na(2)B(5)O(8)(OH).2H(2)O is made up of Na-O polyhedra, and [B(5)O(8)(OH)](2-) polyborate anions. Transmittance spectrum is performed on the Na(2)B(5)O(8)(OH).2H(2)O crystal, which shows an absorption edge less than 190 nm in the UV region. The powder second-harmonic generation intensity measured by the Kurtz-Perry method indicates that Na(2)B(5)O(8)(OH).2H(2)O is about half that of KH(2)PO(4) (KDP).