Explorations of New SHG Materials in Mercury Iodate Sulfate System**

Through systematic experiments, two novel mercury iodate sulfates, namely, Hg2 (IO3 )2 (SO4 )(H2 O) and Hg2 (IO3 )2 (SO4 ) were obtained. They crystallize in monoclinic space group C2 and C2/c, respectively. Hg2 (IO3 )2 (SO4 )(H2 O) exhibits the [Hg(IO3 )]+ polar cationic layer inherited from Hg(IO3 )2 and the three-dimensional (3D) framework inherited from HgSO4 . This enables Hg2 (IO3 )2 (SO4 )(H2 O) to generate a strong second harmonic generation (SHG) response of 6 times that of KH2 PO4 (KDP). The structure of Hg2 (IO3 )2 (SO4 ) is very similar to that of Hg2 (IO3 )2 (SO4 )(H2 O), and they can be transformed into each other. Hg2 (IO3 )2 (SO4 )(H2 O) shows a large optical band gap of 3.98 eV and a high dehydration temperature of 250 °C. This study indicates that by reasonable design, the introduction of multiple functional groups into a compound may combine their advantages to achieve good overall optical performance.