LAUSR

Abstract Two new isostructural lead borates, Pb8Mg(BO3)6 and Pb8Ca(BO3)6, have been synthesized via high temperature solution method. The single crystal structures of title compounds contain ∞[Pb8B6O18]2- double layers composed of planar BO3 triangles, Pb(2)O9 and distorted Pb(1)O5 polyhedra, these layers condense in c-axis, and the MgO6 (or CaO6) polyhedra fill into the layers, forming a three-dimensional framework. The stereochemical activity of lone pair (SCALP) electrons were found in the Pb(1)O5 polyhedra, which combine with the BO3 units, generating strong optical anisotropy. The calculated birefringences of Pb8Mg(BO3)6 and Pb8Ca(BO3)6 using first-principles method are 0.15@1064 nm and 0.12@1064 nm, respectively, which are comparable to the commercial α-BaB2O4 (α-BBO) crystal and imply that they probably can be used as birefringent materials. The electronic structures, density of states of title compounds were calculated by density functional theory (DFT). Meanwhile, the TG-DSC curves, infrared spectral and UV–Vis–NIR diffuse reflectance spectral were measured.