Hg16O12(NO3)6F2(H2O): A Mercury-Rich Nitrate Oxyfluoride with Diverse Triple-Coordinated Mercury-Based Units That Exhibits an Unparalleled [(Hg16O12F2(H2O))6+]∞ Cationic Framework and a Large Birefringence.

Designing new compounds based on anion regulation has been widely favored due to the production of diverse crystal structures and excellent optical properties. Here, a new nitrate oxyfluoride, Hg16O12(NO3)6F2(H2O), has been obtained through a hydrothermal reaction. It crystallizes in the centric Ibca space group and shows a novel three-dimensional [(Hg16O12F2(H2O))6+]∞ cationic framework composed of interconnected HgO2F, HgO3, and HgO2(H2O) units, with isolated NO3- groups as balanced anions to build the whole structure. Notably, the HgO2F and HgO2(H2O) units are first presented here among mercury (Hg)-based compounds. Additionally, Hg16O12(NO3)6F2(H2O) exhibits a large birefringence of 0.17 at 546 nm. This work enriches the multiformity of Hg-based compounds and provides a route for developing promising birefringent materials.