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

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.