Synthesis, structures and properties of two new nitrate optical materials: Rb3ZnNO3Cl4 and Rb5Na(NO3)4Cl2

Two new nitrates Rb3ZnNO3Cl4 and Rb5Na(NO3)4Cl2 have been synthesized by hydrothermal method, and they are crystallized in orthorhombic space group Pnma (no. 62) and tetragonal space group P4/mnc (no. 128), respectively. ZnCl4 and RbO3Cl6 polyhedron, NaO4Cl2 and RbO8Cl2 polyhedron are connected by sharing O or Cl atoms to construct three-dimensional (3D) frameworks with trigonal plane NO3 units as pseudo-layers, in which different types of channels are presented. In addition, Rb5Na(NO3)4Cl2 exhibits a perovskite-related framework, and Rb3ZnNO3Cl4 crystals is grown with dimensions up to 5×4.5×1 mm3. Notably, these two compounds have short UV cut-off edge (below 222 nm and 238 nm, respectively). Theoretical calculations indicate that the birefringence enhancement is mainly derived from π-conjugated NO3 units.