From (C₁₂H₉N₂)₂TeBr₆·2H₂O to (C₁₂H₉N₂)₂TeBr₆: Dehydration-Driven Crystal Reorganization for Birefringence...

Birefringent crystals are essential in laser modulation, optical communication, and imaging systems. This paper reports two tellurium-based hybrid birefringent crystals─(C₁₂H₉N₂)₂TeBr₆·2H₂O and (C₁₂H₉N₂)₂TeBr₆─composed of Te⁴⁺-centered octahedral units and [C₁₂H₉N₂]⁺ π-conjugated organic cations. The hydrate converts to the anhydrate via thermal dehydration, a process in which water removal eliminates steric hindrance, promoting a more ordered molecular arrangement. Optical measurements show significantly enhanced birefringence after dehydration. The value at 546 nm increases from 0.17 to 0.31, nearly doubling. These findings highlight the potential of such materials for advanced optical applications that require high birefringence.