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Benefiting from the planar π-conjugated (HxC3N3O3)x−3 (x = 0–3) groups, cyanurate crystals have recently become a research hotspot in birefringent materials. Herein, by combining the (HxC3N3O3)x−3 (x = 0–3) group with the (CN3H6)+ cationic group, two metal-free cyanurates, GU(H2C3N3O3) (I) and GU3(H2C3N3O3)3(H3C3N3O3) (II), were obtained by the hydrothermal method. These compounds have wide band gaps (∼5 eV) and a large birefringence (∼0.40@400 nm), demonstrating their potential to be ultraviolet birefringent crystals. Moreover, first-principles calculations indicate that their large birefringence values originated from the synergistic effect of the (CN3H6)+ cations and (HxC3N3O3)x−3 (x = 0–3) groups. These findings provide a new design strategy for exploring low-cost UV birefringent crystals with a large birefringence. [ABSTRACT FROM AUTHOR]

A new noncentrosymmetric borate, Na3Y3(BO3)4, was grown in the Na2O–B2O3–NaF flux system. Its open-framework structure features a large hexagonal tunnel (5.92 Å in diameter), which is extremely rare in borates. First-principles calculations on its kinetic stability and optical properties were performed. [ABSTRACT FROM AUTHOR]

An alkali metal selenite chloride, Rb2SeOCl4·H2O, has been hydrothermally synthesized and structurally characterized. It is the first example of an alkali metal selenite halide in the literature. The compound crystallizes in the noncentrosymmetric (NCS) space group, Cmc21(36), of the orthorhombic system with a = 10.342(3) Å, b = 10.124(3) Å, c = 9.158(3) Å, and α = β = γ = 90°. The anionic [SeOCl4]2− groups are arranged in the crystal in nearly the same direction, giving rise to a relatively large macroscopic dipole moment, causing the compound to display second harmonic generation (SHG) eight times as strong as that of KDP, measured using the Kurtz–Perry method on powders. First-principle density functional theory (DFT) calculations were carried out to interpret the relationship between the crystal structure and properties. [ABSTRACT FROM AUTHOR]

Two new quaternary selenides, namely Ba4Ga4SnSe12 and Ba6Ga2SnSe11, have been synthesized for the first time, representing the first two members in the A/M/Sn/Q (A = alkaline-earth metal; M = Al, Ga, In; Q = S, Se, Te) system. Ba4Ga4SnSe12 crystallizes in the non-centrosymmetric space group P4̅21/c of the tetragonal system and has a three-dimensional structure. Its three-dimensional framework is built up from corner-sharing GaSe4 and SnSe4 tetrahedra with eight-coordinated Ba2+ cations residing in the cavities. Ba6Ga2SnSe11 crystallizes in a new structure type in the monoclinic centrosymmetric space group P21/c. The structure of Ba6Ga2SnSe11 features a zero-dimensional structure containing totally isolated distorted SnSe4 tetrahedra and a discrete Ga2Se7 unit with Ba2+ cations located between them. On the basis of the diffuse-reflectance spectra, the band gaps are 2.16 (2) eV and 1.99 (2) eV for Ba4Ga4SnSe12 and Ba6Ga2SnSe11 respectively. In addition, the electronic structure calculation of Ba4Ga4SnSe12 indicates that it is a direct-gap semiconductor with the band gap mainly determined by the [Ga4SnSe12]8− anionic framework. [ABSTRACT FROM AUTHOR]

A new ternary selenostannate Ba6Sn6Se13 has been synthesized by a high temperature solid-state method. The compound crystallizes in the non-centrosymmetric orthorhombic space group P212121 and may be represented as Ba6Sn52+Sn4+Se13 with mixed valence Sn atoms. Sn4+ cations lie in a tetrahedral environment, while Sn2+ cations are found in two kinds of coordination environments: the trigonal pyramid and quadrangular pyramid. SnSen (n = 3, 4, 5) polyhedra are further connected to generate a three-dimensional framework with Ba2+ residing in cavities. Ba6Sn6Se13 shows moderate nonlinear optical response and is the first reported NLO compound in the Ba–Sn–Se system. In addition, diffuse reflectance spectroscopy measurement indicates that the band gap of Ba6Sn6Se13 is 1.52(2) eV and thermal analysis suggests that the compound melts incongruently. The theoretically calculated SHG response and band gap are in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

The high pressure behaviour of a cubic dense inorganic–organic framework [DABCOH22+][K(ClO4)3] (DABCOH22+ = diazabicyclo[2.2.2]octane-1,4-diium) has been systematically studied via synchrotron X-ray powder diffraction, over the range of 0–3.12 GPa. The framework [DABCOH22+][K(ClO4)3] shows a more rigid response, with a bulk modulus of 30(1) GPa and an axial compressibility of 7.6(4) × 10−3 GPa−1, compared with ZIF-8 and the dense hybrid solar cell perovskite CH3NH3PbI3. Density functional theory calculations reveal that the structural change in [DABCOH22+][K(ClO4)3] is attributed to the contraction of the KO12 polyhedra, which consequently results in the rotation of the perchlorate linkers and synergistic movement of the DABCOH22+ guest. Further extensive theoretical calculations of full elastic tensors give full mapping of the Young's moduli, shear moduli and Poisson's ratios of [DABCOH22+][K(ClO4)3], which are in the range of 31.6–36.6, 12.3–14.6 GPa and 0.2–0.32, respectively. The Young's and shear moduli of [DABCOH22+][K(ClO4)3] are larger than those of cubic MOF-5, ZIF-8 and CH3NH3PbI3. In addition, the narrow range of Poisson's ratios in [DABCOH22+][K(ClO4)3] indicates its very isotropic nature in response to biaxial stress. [ABSTRACT FROM AUTHOR]

A new sulfide, SnGa2GeS6, has been synthesized, which represents the first member in the quaternary Sn/M/M′/Q (M = Ga, In; M′ = Si, Ge; Q = S, Se, Te) system. It adopts a new structure type in the non-centrosymmetric space group Fdd2. In the structure, Sn2+ is coordinated to a distorted square-pyramid of five S atoms, demonstrating the stereochemical activity of the lone electron pair, while the Ge atom and Ga atom are both tetrahedrally coordinated to four S atoms. The SnS5 square-pyramids and the MS4 (M = Ga, Ge) tetrahedra are connected to each other via corner and edge-sharing to generate a three-dimensional framework. The compound exhibits a powder second harmonic generation signal at 2 μm whose strength is about one-fourth that of the benchmark material AgGaS2, which may be explained in view of the macroscopic arrangement of the SnS5 square-pyramids and the MS4 tetrahedra. Moreover, based on UV-vis-NIR spectroscopy measurements and the electronic structure calculations, SnGa2GeS6 has two optical transitions at about 1.12 eV and 2.04 eV respectively. [ABSTRACT FROM AUTHOR]