New Alkaline-Earth Metal Fluoroiodates Exhibiting Large Birefringence and Short Ultraviolet Cutoff Edge with Highly Polarizable (IO3F)2– Units

By the selective fluorination of IO4 in iodates, SrI2O5F2 (SIOF) and Ba­(IO2F2)2 (BIOF) were synthesized successfully. They are the first reported cases of alkaline-earth metal fluoroiodates, and the (IO3F)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 (IO3F)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.