[C(NH2)3]BiCl2SO4: an excellent birefringent material obtained by multifunctional group synergy

Herein, a multifunctional group synergistic strategy was proposed to develop an excellent organic-inorganic hybrid guanidine sulfate material [C(NH2)(3)]BiCl2SO4 (GuBiCl(2)SO(4)), which was constructed with three types of functional groups including planar triangle pi-conjugated [C(NH2)(3)](+) cations, [BiCl2O4](7-) anion polyhedra with stereochemical-active lone pairs and [SO4](2-) tetrahedra. GuBiCl(2)SO(4) possesses a large birefringence (0.143@546 nm), much larger than those of other representative Bi-based/Gu-based compounds containing tetrahedral anionic birefringent crystals. Interestingly, the title compound also displays light-blue emission, which indicates that it is an outstanding bifunctional optical material. The computational analysis revealed that the broadband emission of GuBiCl(2)SO(4) can be attributed to charge transitions from organic [C(NH2)(3)](+) cations to [BiCl2O4](7-) anion polyhedra and the large birefringence stems from the cooperative effect of the planar triangle pi-conjugated [C(NH2)(3)](+) cations, [BiCl2O4](7-) anion polyhedra and [SO4](2-) distorted tetrahedra.