Pyrazinamide–IBr: an organic–inorganic hybrid crystal exhibiting giant optical anisotropy

Abstract

A novel organic–inorganic hybrid crystal, pyrazinamide–IBr (PZA–IBr, C₅H₅N₃OIBr), was successfully synthesized using a facile in situ reduction method. PZA–IBr exhibits remarkable birefringence (Δn_exp = 0.524 at 550 nm, Δn_cal = 0.760 at 550 nm), surpassing those of commercially available birefringent crystals. PZA–IBr also has a moderate band gap of 2.32 eV. Structural and theoretical analyses reveal that the large birefringence originates from both the planar π-conjugated PZA and linear IBr molecules and is enhanced by the N–I halogen bonds, N–H⋯O hydrogen bonds, and C–H⋯π interactions. This work demonstrates the effectiveness of combining a heterocyclic molecule with an interhalogen molecule to create high-performance birefringent crystals.