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

Abstract

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.