An effective pathway to design and synthesize UV birefringent crystals via rational assembly of -conjugated [CO₃]^2- and [NO₃]^- triangles

Planar MO3 (M = B, C, N) units have frequently been considered important structural components of novel birefringent crystal materials. An efficient approach for constructing new functional crystals is to simultaneously assemble multiple structural motifs together. Two compounds, Na3Rb6(CO3)(3)(NO3)(2)X center dot 6H(2)O (X = Br and Cl), were synthesized by the integration of three kinds of anionic groups. More interestingly, the [CO3](2-) and [NO3](-) groups in Na3Rb6(CO3)(3)(NO3)(2)X center dot 6H(2)O are all coplanar with the aid of [NaO7](13-) polyhedra, which can enhance the anisotropic polarizability. Na3Rb6(CO3)(3)(NO3)(2)X center dot 6H(2)O have a large theoretical birefringence of similar to 0.165 at 1064 nm and possess a short UV cut-off edge of similar to 230 nm. Additionally, the two compounds exhibit good crystal growth habits. These properties illustrate that Na3Rb6(CO3)(3)(NO3)(2)X center dot 6H(2)O are promising UV birefringent crystals.