Hg[CS(NH₂)₂]₄(SiF₆): a fluorosilicate crystal with large birefringence achieved via multi-functional group...

Area of Science:

• Materials Science
• Crystallography
• Optics

Background:

• Hexafluorosilicates possess wide band gaps and short UV cutoff edges, but limited birefringence due to low SiF6 group anisotropy restricts their use in optical materials.
• Enhancing the birefringence of hexafluorosilicates is crucial for developing advanced optical functional materials.

Purpose of the Study:

• To develop a novel method for enhancing the birefringence of hexafluorosilicate compounds.
• To synthesize and characterize the first mercury-based hexafluorosilicate birefringent crystal.

Main Methods:

• Incorporation of thiourea ligands and Hg2+ ions into the hexafluorosilicate system.
• Synthesis of the Hg-based hexafluorosilicate crystal, Hg[CS(NH2)2]4(SiF6).
• Structural analysis and birefringence measurements (experimental and calculated).

Main Results:

• Successful synthesis of Hg[CS(NH2)2]4(SiF6), the first Hg-based hexafluorosilicate birefringent crystal.
• The crystal structure features interconnected SiF6 octahedra and Hg[CS(NH2)2]4 clusters linked by hydrogen bonding.
• Achieved a high birefringence of 0.145 (experimental) at 546 nm, comparable to commercial α-BaB2O4 and superior to other inorganic hexafluorosilicates.

Conclusions:

• The proposed method effectively enhances the birefringence of hexafluorosilicate compounds.
• Hg[CS(NH2)2]4(SiF6) represents a promising new birefringent material for optical applications.
• This study opens avenues for designing high-performance optical materials based on modified hexafluorosilicates.