From NaGa(IO₃)₃F to NaGa(IO₃)₂F₂ and NaGa(IO₃)₄: The Effects of Chemical Substitution between F^– Anions and IO₃^– Groups on the Structures and Properties of Gallium Iodates

Introducing F^– anions or substituting F^– anions with IO₃^– groups has been proven to be ideal strategies for designing novel noncentrosymmetric (NCS) and polar materials, yet systematic investigation into the effect of F^– anions or the substitution of IO₃^– for F^– anions on structures and properties remains rarely explored. Herein, two new gallium iodates, NaGa­(IO₃)₂F₂ (<b>1</b>) and NaGa­(IO₃)₄ (<b>2</b>), were successfully designed and synthesized based on NaGa­(IO₃)₃F by introducing more F^– anions and replacing F^– anions with IO₃ groups, respectively. Structurally, in compound <b>1</b>, the adjacent [GaF₃(IO₃)₃]^3– polyanions are connected in an antiparallel manner, resulting in a complete cancellation of local polarity. While in compound <b>2</b>, all IO₃ groups in 2D [Ga­(IO₃)₄]_∞^– layers are aligned, leading to large macroscopic polarization. Additionally, chemical substitution also results in a qualitative improvement in the functional properties of compound <b>2</b>. It possesses strong SHG response (12 × KDP @1064 nm) and broad optical transparency, coupled with large birefringence (0.21 @1064 nm), showcasing its promise as a promising nonlinear optical (NLO) crystal. The effects of chemical substitution between F^– anions and IO₃^– groups on the structures and properties are discussed in detail.