Ba 1.09 Pb 0.91 Be 2 (BO 3 ) 2 F 2 : The First Pb-Containing Beryllium Borate Fluoride with Trigonal Prismatic PbO 6 and 2D [Be 3 B 3 O 6 F 3 ] ∞ Layers.

Ba 1.09 Pb 0.91 Be 2 (BO 3 ) 2 F 2 (BPBBF), a previously unreported lead-containing beryllium borate fluoride, has been successfully grown through a high-temperature flux method. Its structure is solved by single-crystal X-ray diffraction (SC-XRD), and it is optically characterized via infrared, Raman, UV-vis-IR transmission, and polarizing spectra as well. SC-XRD data suggests that it can be indexed by a trigonal unit cell (space group P 3 m 1) with lattice parameters a = 4.7478(6) Å, c = 8.3856(12) Å, Z = 1, and V = 163.70(5) Å. This material could be considered as a derivative of the Sr 2 Be 2 B 2 O 7 (SBBO) structural motif. It consists of 2D [Be 3 B 3 O 6 F 3 ] ∞ layers in the crystallographic ab plane, with divalent Ba 2+ or Pb 2+ cations serving as spacers among the adjacent layers. Ba and Pb were found to adopt a disordered arrangement in the trigonal prismatic coordination within the BPBBF structural lattice, which is evidenced by both structural refinements against SC-XRD data and energy dispersive spectroscopy. The UV absorption edge (279.1 nm) and birefringence (Δ n = 0.054@ 546.1 nm) of BPBBF are confirmed by UV-vis-IR transmission and polarizing spectra, respectively. The discovery of this previous unreported SBBO-type material, BPBBF, along with other reported analogues such as Ba M Be 2 (BO 3 ) 2 F 2 ( M = Ca, Mg, and Cd), provide a prodigious example for tuning the bandgap, birefringence, and short UV absorption edge via simple chemical substitution.