Pb₁₀O₄(BO₃)₃I₃: a new noncentrosymmetric oxyborate iodide synthesized by the straightforward hydrothermal method

Borate iodide has interesting functional properties but is challenging for synthesizing. A new non-centrosymmetric borate iodide Pb10O4(BO3)3I3 has been synthesized by a straightforward hydrothermal method. Pb10O4(BO3)3I3 crystallizes in the noncentrosymmetric monoclinic space group Cc. In its structure, the basic structural building units [Pb10O8] connect with BO3 groups to form two-dimensional (2D) [Pb10O8B2O6]∞ layers stacked along the b-axis, which are further linked by the B(1)O3 groups to constitute a 3D framework. Interestingly, in this structure, some oxygen atoms are coordinated by four Pb2+ cations to form [OPb4] groups, rather than directly connecting with B3+ cations. Therefore, this compound belongs to a new type of borate iodide, oxyborate iodide. To the best of our knowledge, this is the first reported oxyborate iodide. In addition, its functional properties including second harmonic generation (SHG) response, UV-vis-NIR diffuse reflectance and IR spectra were also investigated. The origin of the SHG effect was studied by dipole moment calculations and structure comparison.