Synthesis, structure and properties of nonlinear optical crystal Li(H2O)4B(OH)4·2H2O

• The crystal Li(H2O)4B(OH)4·2H2O was synthesized via hydrothermal method.
• It is composed of B(OH)4, Li(H2O)4 and H2O units.
• The SHG efficiency of Li(H2O)4B(OH)4·2H2O is about 0.8 times that of KDP.
• The SHG response originates from the cooperation of BO4 and LiO4 units.

Single crystal of Li(H2O)4B(OH)4·2H2O has been synthesized via hydrothermal method and its structure was determined by single crystal X-ray diffraction. The space group of Li(H2O)4B(OH)4·2H2O is P3 with cell parameters a = b = 6.5601(4) Å, c = 6.1748(3) Å, and Z = 1. The crystal lattice structure is composed of four B(OH)4 tetrahedra, one Li(H2O)4 tetrahedron and two isolated water molecules. Powder X-ray diffraction (XRD), infrared (IR) spectroscopy, UV-vis-IR diffuse reflectance spectroscopy, powder second-harmonic generation (SHG) measurements and TG/DSC analysis were performed for the title compound. It reveals that the SHG efficiencies of Li(H2O)4B(OH)4·2H2O is about 0.8 times that of KH2PO4 (KDP). The direction and magnitude of the dipole moments in BO4 and LiO4 units of Li(H2O)4B(OH)4·2H2O have been quantified using the bond-valence approach, which shows that the SHG response originates from the cooperation of BO4 and LiO4 units along c axis.

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