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

Abstract

Herein, a multifunctional group synergistic strategy was proposed to develop an excellent organic–inorganic hybrid guanidine sulfate material [C(NH₂)₃]BiCl₂SO₄ (GuBiCl₂SO₄), which was constructed with three types of functional groups including planar triangle π-conjugated [C(NH₂)₃]⁺ cations, [BiCl₂O₄]⁷⁻ anion polyhedra with stereochemical-active lone pairs and [SO₄]²⁻ tetrahedra. GuBiCl₂SO₄ 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 GuBiCl₂SO₄ 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 π-conjugated [C(NH₂)₃]⁺ cations, [BiCl₂O₄]⁷⁻ anion polyhedra and [SO₄]²⁻ distorted tetrahedra.