α- and β‑(C₄H₅N₂O)(IO₃)·HIO₃: Two SHG Materials Based on Organic–Inorganic Hybrid Iodates

Organic–inorganic hybrid nonlinear optical (NLO) materials are highly anticipated because of the integration of both merits of the organic and inorganic moieties. Herein, the 2-pyrimidinone cation (C₄H₅N₂O)⁺ has been incorporated into the iodate system to form two polymorphic organic–inorganic hybrid iodates, namely, α- and β-(C₄H₅N₂O)(IO₃)·HIO₃. They crystallize in different polar space groups (Ia and Pca2₁), and their structures feature one-dimensional (1D) chain structures composed of (C₄H₅N₂O)⁺ cations, IO₃^– anions, and HIO₃ molecules interconnected via hydrogen bonds. α- and β-(C₄H₅N₂O) (IO₃)·HIO₃ exhibit strong and moderate second-harmonic-generation (SHG) responses of 6.4 and 0.9 × KH₂PO₄ (KDP), respectively, the same band gaps of 3.65 eV, and high powder laser-induced damage threshold (LIDT) values [51 and 57 × AgGaS₂ (AGS)]. The results of theoretical calculations revealed that the large SHG effect of α-(C₄H₅N₂O)(IO₃)·HIO₃ originated from the IO₃ and HIO₃ groups. This work indicates that (C₄H₅N₂O)⁺ is a potential group for designing new NLO materials with brilliant optical performances.