Synthesis, Structure, and Characterization of d⁰ Transition-Metal Iodate: BaTi(IO₃)₆·0.5H₂O

A new noncentrosymmetric (NCS) d⁰ transition-metal (TM) iodate BaTi­(IO₃)₆·0.5H₂O has been successfully synthesized by the typical hydrothermal method. The single-crystal X-ray diffraction shows that BaTi­(IO₃)₆·0.5H₂O crystallizes in the polar trigonal space group R3 (no. 146) with a = b = 11.1920(12) Å, c = 24.006(3) Å. The reported compound features zero-dimensional (0D) [Ti­(IO₃)₆]^2– clusters that are separated by Ba²⁺ cations and bound water in the structure. By comparing BaTi­(IO₃)₆·0.5H₂O with the centrosymmetric (CS) α- and β-BaTi­(IO₃)₆ that were reported before, it can be found that the bound water plays an important role for the formation of NCS structure for BaTi­(IO₃)₆·0.5H₂O. In addition, based on the powder second harmonic (SHG) measurement, BaTi­(IO₃)₆·0.5H₂O can achieve type-I phase matching with a moderate SHG effect (∼1 × KDP). The source of SHG effect was analyzed by dipole moment calculation and structure comparison. UV–vis–NIR diffuse reflectance spectroscopy, infrared spectroscopy, and thermogravimetric measurements are also presented.