Li0.8Mg2.1B2O5F: the first borate fluoride with magnesium–oxygen–fluorine octahedral chains

Abstract

The first alkali metal and magnesium mixed borate fluoride, Li_0.8Mg_2.1B₂O₅F, was prepared by the high-temperature solution method. It crystallizes in the monoclinic space group P2₁/n (no. 14) with lattice constants a = 3.0881(4) Å, b = 13.6020(2) Å, c = 9.6563(1) Å, β = 91.744(9)°, Z = 4. In the structure, a special magnesium–oxygen–fluorine octahedral chain is found in borates for the first time. The octahedral chains are linked into a three-dimensional framework containing tunnels with ¹_∞[LiO₄]⁷⁻ chains and isolated B₂O₅ groups filling in. The differences of octahedral chains in Li_0.8Mg_2.1B₂O₅F and magnesium inosilicate minerals are discussed. The TG-DSC curves, IR spectrum and UV-Vis-NIR diffuse reflectance spectrum were measured.