By the selective fluorination of IO 4 in iodates, SrI 2 O 5 F 2 (SIOF) and Ba(IO 2 F 2 ) 2 (BIOF) were synthesized successfully. They are the first reported cases of alkaline-earth metal fluoroiodates, and the (IO 3 F) 2− units in SIOF were discovered for the first time to the best of our knowledge. BIOF possesses the shortest UV cutoff edge (230 nm), and SIOF has the largest birefringence (cal. 0.203 at 532 nm) among the reported fluoroiodates. The highly polarizable (IO 3 F) 2− , with high polarizability anisotropy, induces a large birefringence in SIOF by theoretical calculation. This work will contribute to enlarge the structural diversity and provide a good choice for the material design in fluoroiodates.

The first zinc iodate fluoride, ZnIO 3 F, was synthesized by the Zn 2+ cation, the IO 3 group, and fluorine ion, where Zn 2+ is coordinated by O atoms from iodate and F atoms to form the ZnO 4 F 2 polyhedron. It has outstanding optical characteristics, including large birefringence (Δ = 0.219 at 546 nm), wide band gap (E g = 4.2 eV), and good thermal stability (over 475 °C), showing a subtle balance between the wide band gap and birefringence.

Two new alkaline-earth-metal fluoroiodate compounds, BaI2O5F2 and BaIO2F3, were successfully synthesized by replacing the O atoms in the iodates with F atoms via the hydrothermal method. They crystallize in centrosymmetric...