RbY(SO4)2·4H2O: A new ultraviolet birefringent crystal

The SO 4 tetrahedral group exhibits a low degree of polarization anisotropy, leading to a minimal level of birefringence of sulfates. Our report introduces a novel sulfate compound, RbY(SO 4 ) 2 ·4H 2 O, which exhibits exceptional birefringence in deep ultraviolet sulfates. This crystal possesses dimensions of 6 mm × 4 mm × 1 mm and was synthesized using a straightforward technique involving the evaporation of an aqueous solution. The structure of this substance is characterized by a unique arrangement of SO 4 tetrahedra YO 9 polyhedra, and H 2 O molecules. Each SO 4 moiety contribution two oxygen atoms to share edges with a neighboring YO 9 polyhedron, resulting in significant deformation of these groups. The unique arrangement of edge-sharing arrangement in RbY(SO 4 ) 2 ·4H 2 O results in a birefringence of about 0.045@546 nm. This sets a new record for sulfates in the deep ultraviolet range that have similar non-π-conjugated anionic groups. We elucidate UV–Vis–NIR diffuse-reflection, IR spectra, transmission spectra, and conduct theoretical calculations. These fascinating discoveries will improve our understanding of sulfates and provide valuable insights for studying deep-UV sulfates with strong birefringence.