A new tin iodate fluoride, Sn­(IO3)2F2, was meticulously designed based on Sn­(IO3)4 with an intriguing chemical tailoring transformation from the centrosymmetric to noncentrosymmetric structure. Sn­(IO3)2F2 crystallizes in polar space group P21 and features an one-dimensional chain constructed by IO3 and SnO4F2. It has an enlarged band gap (4.08 eV) compared to the Sn­(IO3)4 (3.96 eV) because of the introduction of strong electronegative F–. Also, powder second-harmonic generation (SHG) measurements revealed that Sn­(IO3)2F2 is a phase-matchable nonlinear crystal with a strong SHG response about 3 times that of KH2PO4. Theoretical investigations elaborated that its large nonlinearity originates from the synergistic effect of lone pairs on IO3 and flexible dipole moments of SnO4F2 polyhedra.

The first alkali-metal nitrate isocyanurates, A­(H3C3N3O3)­(NO3) (A = K, Rb), were synthesized by the tactic of introducing (NO3)− into isocyanurate with a mild hydrothermal technique. They crystallized into the same monoclinic centrosymmetric (CS) space group P21/c, which featured a 2D [(H3C3N3O3)­(NO3)]∞ layered structure separated by K+ and Rb+ cations, respectively. Both compounds exhibited short ultraviolet cutoff edges (λcutoff = 228 and 229 nm) and large birefringences (Δn = 0.253 and 0.224 at 546.1 nm). More importantly, in comparison with most of the isocyanurates and nitrates, they have better thermal stability with decomposition temperatures up to 319.8 and 324.4 °C. In addition, our theoretical calculations reveal that the π-conjugated groups play significant roles in improving the optical anisotropy. Remarkably, introducing a π-conjugated inorganic acid radical (NO3)− into isocyanurate is an extremely meaningful strategy to explore new UV birefringent crystals.