Anionic configuration extension induced birefringence enhancement in vanadium iodate oxyfluorides.

Rb2VOF4(IO2F2) and RbVO2F(IO3) were successfully synthesized. In their structures, the connectivity between the V-O/F polyhedra and I-O/F units evolves from isolated [VOF4(IO2F2)] clusters in Rb2VOF4(IO2F2) to extended two-dimensional anionic layers constructed from [VO2F(IO3)2] chains in RbVO2F(IO3). This structural evolution further enhances the structural anisotropy, thereby significantly increasing the birefringence from 0.079 to 0.129 at 1064 nm. Additionally, the structural transition and performance comparison were also discussed in detail.