Polymorphic Pb14O8I12 and Pb7O4I6 oxyhalides featuring unprecedented [O8Pb14] clusters with broad IR transparency

Wide transmittance range is an essential factor for the design of infrared optical materials. Traditionally, designs mid-far crystals have focused on oxygen-free systems chalcogenides and pnictides. Nevertheless, introduction elements with large atomic numbers, such as lone-pair cation Pb2+ halogen anion I−, based oxyhalides, can broaden range. Thus, two new polymorphs Pb(II)-containing Pb14O8I12 (α-POI) Pb7O4I6 (β-POI), are successfully synthesized via high-temperature solution method. Interestingly, they crystallize in same space group, $$P\bar 1$$ , present unprecedented [O8Pb14] clusters from perspective oxo-centered [OPb4] basic units. Remarkably, POI exhibits a quite wide transparent (0.47–16.0 µm), which enlightens oxyhalides prominent properties. Additionally, first principles calculations show that birefringence (0.139 0.108 α- β-POI at 1064 nm, respectively), makes promising