Mg2Pb2Si2O7F2: a new lead-containing alkali earth metal silicate fluoride with a short cutoff edge

Abstract

A new silicate fluoride, Mg₂Pb₂Si₂O₇F₂, has been successfully synthesized using a high-temperature solution method. It crystallizes in the orthorhombic space group Pbcn (No. 60). Mg₂Pb₂Si₂O₇F₂ is the first lead-containing alkali earth metal silicate fluoride. The optical characterization indicates that Mg₂Pb₂Si₂O₇F₂ possesses a wide transparent window. To confirm the coordination environment of Si and its thermostability, infrared spectra and thermal behaviors were also analyzed. First-principles calculations were also implemented for a better understanding of the relationship between the structure of Mg₂Pb₂Si₂O₇F₂ and its properties. Additionally, to further explore the structural novelty of Mg₂Pb₂Si₂O₇F₂, its structure is compared with anionic structures of silicate fluorides with alkali metals, alkaline earth metals or lone pair metal cations. Interestingly, the results indicate that the isolated [Si₂O₇] dimer is rare among the above systems, which enriches the structural chemistry of silicate fluorides.