Hydrogen Bond-Assisted Structural Regulation Enables Large Birefringence in Two Antimony Oxalofluoride Crystals

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Antimony-based compounds are explored for optical applications.
• Oxalofluoride materials offer unique structural and electronic properties.
• Birefringent materials are crucial for optical devices.

Purpose of the Study:

• Synthesize novel antimony-based oxalofluoride crystals.
• Investigate their optical properties, including birefringence and band gap.
• Elucidate the structural factors contributing to optical anisotropy.

Main Methods:

• Solvent evaporation method for crystal synthesis.
• Single-crystal X-ray diffraction for structural determination.
• Optical spectroscopy and theoretical calculations for property analysis.

Main Results:

• Two new crystals, (NH4)2Sb(C2O4)1.5F2·H2O and (NH4)Sb(C2O4)F2·H2O, were synthesized.
• Large birefringence values (0.24 and 0.22) and wide optical band gaps (3.93 and 3.75 eV) were observed.
• Structural analysis revealed [SbO4F2]7- pentagonal pyramids and π-conjugated oxalate groups linked by hydrogen bonds.

Conclusions:

• The observed optical anisotropy results from the interplay of lone-pair electrons, π-conjugated anions, and hydrogen bonding.
• This study presents a molecular design strategy for UV birefringent materials.
• Cooperative structural modulation is key for tailoring material properties.