Facile Syntheses of Ba2[B4O7(OH)2] and Na[B5O7(OH)2](H2O) Borate Salts Exhibiting Nonlinear Optical Activity in the Ultraviolet

Two novel noncentrosymmetric metal borates, Ba 2 [B 4 O 7 (OH) 2 ] ( 1 ) and Na[B 5 O 7 (OH) 2 ](H 2 O) ( 2 ), have been obtained by hydrothermal and surfactant–thermal means. Compound 1 consists of novel one-dimensional borate chains formed by B 3 O 9 and B 3 O 8 rings, assembled into a three-dimensional (3D) framework by Ba 2+ cations. The structure of 2 exhibits double-helical chains constructed from B 5 O 10 primary building units, which are interconnected via Na + cations and H-bonding interactions to generate a 3D framework. Second-harmonic-generation (SHG) measurements show that 1 shows a phase-matching powder SHG response of ∼2.2 × KH 2 PO 4 (KDP), while 2 exhibits a weak SHG response. The cutoff edges of 1 and 2 are ∼242 and ∼221 nm, respectively, which suggests that they are potential ultraviolet nonlinear optical (NLO) materials. Band structures and NLO properties have also been theoretically studied.