Assisting the Effective Design of Polar Iodates with Early Transition-Metal Oxide Fluoride Anions.
Hongwei YuMatthew L NisbetKenneth R PoeppelmeierPublished in: Journal of the American Chemical Society (2018)
Polar materials are of great technical interest but challenging to effectively synthesize. That is especially true for iodates, an important class of visible and mid-IR transparent nonlinear optical (NLO) materials. Aiming at developing a new design strategy for polar iodates, we successfully synthesized two sets of polymorphic early transition-metal (ETM) oxide-fluoride iodates, α- and β-Ba[VFO2(IO3)2] and α- and β-Ba2[VO2F2(IO3)2]IO3, based on the distinct structure-directing properties of oxide-fluoride anions. α- and β-Ba[VFO2(IO3)2] contain the trans-[VFO2(IO3)2]2- polyanion and crystallize in the nonpolar space groups Pbcn and P212121. In contrast, α- and β-Ba2[VO2F2(IO3)2]IO3 contain the cis-[VO2F2(IO3)2]3- Λ-shaped polyanion and crystallize in the polar space groups Pna21 and P21, respectively. Detailed structural analyses show that the variable polar orientation of trans-[VFO2(IO3)2]2- polyanions is the main cause of the nonpolar structures in α- and β-Ba[VFO2(IO3)2]. However, the Λ-shaped configuration of cis-[VO2F2(IO3)2]3- polyanions can effectively guarantee the polar structures. Further property measurements show that polar α- and β-Ba2[VO2F2(IO3)2]IO3 possess excellent NLO properties, including the large SHG responses (∼9 × KDP), wide visible and mid-IR transparent region (∼0.5-10.5 μm), and high thermal stability (up to 470 °C). Therefore, combining cis-directing oxide-fluoride anions and iodates is a viable strategy for the effective design of polar iodates.