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Nonlinear optical (NLO) crystals are widely used in various fields. The introduction of lone-pair cations is regarded as an effective strategy to explore NLO crystals. In this work, two novel lead phosphite halides, centrosymmetric Pb6(HPO3)(H2PO3)Cl9and noncentrosymmetric Pb6(HPO3)2Br8(H2O)·H2O, were obtained via a hydrothermal method. Pb6(HPO3)(H2PO3)Cl9is the first reported lone-pair metal phosphite with two kinds of phosphite groups (HPO32–and H2PO3–) and Pb6(HPO3)2Br8(H2O)·H2O is the first inorganic NLO phosphite halide with a phase-matchable SHG effect of 1.02 × KDP. In addition, the Pb-centered polyhedral units of PbOCl4, PbOCl6, PbO2Cl5, PbO2Br5, PbOBr6, and PbO3(H2O)Br3in these two structures have never been reported before. An in-depth study on the structure–property relationship of the two compounds with halogen substitution is also performed.

Designing short-wavelength nonlinear-optical (NLO) crystals is of vital importance for laser applications. Here, the combination of alkaline-earth metals, d0transition metals, and F atom has generated two new and isostructural fluorides, CaBaZr2F12(CBZF) and CaBaHf2F12(CBHF), which adopt centrosymmetric space group I4/mmm. Taking CBZF and CBHF as the parents, two new fluorides, K2BaZr2F12(KBZF) and K2BaHf2F12(KBHF), with an Imm2 polar structure were obtained via a heterovalent cation substitution strategy. All four compounds feature ZrF8-dodecahedra-built {[Zr2F12]4–}∞chains and show short ultraviolet cutoff edges (<200 nm). KBZF and KBHF show phase-matchable behavior with moderate second-harmonic-generation responses [0.6 and 0.35 × KH2PO4(KDP)] under 1064 nm laser radiation. This work enriches fluorides as promising short-wavelength NLO materials.

Oxychalcogenides are increasingly attracting wide attention because they contain multiple anions that may combine the advantages of oxides and chalcogenides. In this work, two new pentanary oxythiogermanates, Ba3MGe3O2S8[M = Ca (1), Zn (2)], were synthesized by a high-temperature solid-state reaction. They crystallize in the orthorhombic space group Pnma, and their structures contain isolated [Ge3O2S8]8–units constructed by one [GeO2S2] and two [GeOS3] tetrahedra that link with M2+ions to build the {[MGe3O2S8]6–}8chain, representing a new type of oxythiogermanate. Notably, a [ZnS5] square pyramid exists in 2. Their structural chemistry and relationship with relevant structures are analyzed. 1and 2exhibit wide band gaps of 3.93 and 2.63 eV, birefringences of 0.100 and 0.089 at 2100 nm, respectively, and also obvious photocurrent responses. This work may be extended to a family of AE3MIIMIV3O2Q8(AE = alkali-earth metal; MII= Ca, Zn, Cd, Hg; MIV= Si, Ge, Sn; Q = S, Se), and further systematic survey on them can be performed to enrich the study of multifunctional oxychalcogenides.

Designing new compounds based on anion regulation has been widely favored due to the production of diverse crystal structures and excellent optical properties. Here, a new nitrate oxyfluoride, Hg16O12(NO3)6F2(H2O), has been obtained through a hydrothermal reaction. It crystallizes in the centric Ibcaspace group and shows a novel three-dimensional [(Hg16O12F2(H2O))6+]∞cationic framework composed of interconnected HgO2F, HgO3, and HgO2(H2O) units, with isolated NO3–groups as balanced anions to build the whole structure. Notably, the HgO2F and HgO2(H2O) units are first presented here among mercury (Hg)-based compounds. Additionally, Hg16O12(NO3)6F2(H2O) exhibits a large birefringence of 0.17 at 546 nm. This work enriches the multiformity of Hg-based compounds and provides a route for developing promising birefringent materials.