LiK[B ₅ O ₈ (OH)]·1.5H ₂ O: A novel lithium borate with nonlinear optical property

A new acentric borate of LiK[B ₅ O ₈ (OH)]·1.5H ₂ O (1) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectroscopy, thermogravimetric analysis (TGA) and UV spectrum, respectively. The structural analysis shows that 1 crystallizes in the orthorhombic space group C222 ₁ with a = 6.6403(4) Å, b = 11.7638(9) Å, c = 20.5334(13) Å, and Z = 2. In the structure 1, the structural building unit, B ₅ O ₁₀ (OH) cluster, connects with four same ones to form 2-D [B ₅ O ₈ (OH)] _n ^2n- layer with nine-member ring windows. Furthermore, the 2-D layers packed in the -ABCD- mode, which is an unprecedented stacking-mode in layered borates. Second-harmonic generation (SHG) measurements on the powder samples reveal that 1 exhibits SHG efficiency approximately 1.3 times that of KH ₂ PO ₄ (KDP). Also it has a UV cutoff edge below 200 nm.