A UV birefringent crystal: RbNH4(H2C3N3O3)2·2H2O

Abstract

The excellent ultraviolet (UV) birefringent materials are essential to optical systems. Thus, a new UV birefringent crystal RbNH4(H2C3N3O3)2·2H2O has been obtained via the hydrothermal method. It crystallizes in centrosymmetric space group Pnma (No. 62) with the unit cell parameters: a = 6.820(2) Å, b = 16.457(6) Å, c = 11.767(4) Å and Z = 4. The structure of RbNH4(H2C3N3O3)2·2H2O contains the 2∞[H2C3N3O3]− ribbons via hydrogen bonds with the filling of H2O molecules, NH4+ and Rb+ cations. Its calculated birefringence is about 0.40 @ 1064 nm, which comparable or larger than some of the reported largest birefringent values of cyanurates, the experimental UV cutoff edge is down to 223 nm, and the band gap is 5.24 eV. Besides, the first-principles investigation of the electronic properties on the title compound reveals that the parallel alignment of π-conjugated (H2C3N3O3)− anions lead to the short ultraviolet cutoff edge and large birefringence. These results suggest that RbNH4(H2C3N3O3)2·2H2O is a potential UV birefringent material.