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

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.