Synthesis, crystal structure and optical properties of a new lead fluoride borate with isolated [B9O21]15− unit

Pb8B9O21F has been synthesized from the PbO–PbF2–B2O3 system for the first time. It crystallizes in the trigonal system, space group R-3c with unit-cell parameters a = 9.740(3) Å, b = 9.740(3) Å, c = 38.167(15) Å, Z = 6, and volume = 3135.5(8) Å3. The structure of the compound is solved by the direct methods and to the best of our knowledge, Pb8B9O21F is the first structure reported so far with isolated boron–oxygen anionic [B9O21]15−compound. Functional groups present in the sample were identified by Fourier transform infrared spectrum. The Diffuse reflectance spectrum shows that the ultraviolet cutoff edge for the Pb8B9O21F crystal is about 276 nm.