Crystal growth,structural and physical properties of the 5d noncentrosymmetric LaOsSi_3

LaOsSi3 single crystals are synthesized for the first time by an arc melting method. The crystal features a tetrag- onal BaNiSn3-type structure （space group 14mm） which lacks inversion symmetry along the crystallographic c axis and is isostructural with the intensively studied Rashba-type noncentrosymmetric superconductors LaRhSi3 and LaIrSi3. Un- like LaRhSi3 and LaIrSi3 displaying superconductivity, LaOsSi3 shows only metallic behavior over the measured temper- ature range of 2 K-300 K. The Sommerfeld coefficient ]/derived from specific heat is 5.76 mJ.mol-1 -K-2, indicating that LaOsSi3 has a weak electronic correlation effect. The absence of superconductivity in LaOsSi3 may lie in the Os 5d bands in the electronic structure. If it is true, it would be useful to provide complementary knowledge in understanding the relation between conduction and the d bands of M in LaMSi3 compounds （M = transition metals）.     

The structural transformation of monoclinic [(R)-C5H14N2][Cu(SO4)2(H2O)4]·2H2O into orthorhombic [(R)-C5H14N2]2[Cu(H2O)6](SO4)3: crystal structures and thermal behavior

Single crystals of [(R)-C₅H₁₄N₂][Cu(SO₄)₂(H₂O)₄]·2H₂O (1) were grown through the slow evaporation of a solution containing H₂SO₄, (R)-C₅H₁₂N₂ and CuSO₄·5H₂O. These crystals spontaneously transform to [(R)-C₅H₁₄N₂]₂[Cu(H₂O)₆](SO₄)₃ (2) over the course of four days at room temperature. The same single crystal on the same mounting was used for the determination of the structure of (1) and the unit cell determination of (2). A second single crystal of the transformed batch has served for the structural determination of (2). Compound 1 crystallizes in the noncentrosymmetric space group P2₁ (No. 4) and consists of trimeric [Cu(SO₄)₂(H₂O)₄]^2? anions, [(R)-C₅H₁₄N₂]²⁺ cations and occluded water molecules. Compound 2 crystallizes in P2₁2₁2 (No. 18) and contains [Cu(H₂O)₆]²⁺ cations, [SO₄]^2? anions and occluded water molecules. The thermal decompositions of compounds 1 and 2 were studied by thermogravimetric analyses and temperature-dependent X-ray diffraction.     

Syntheses and Single-crystal Structures of New Deficient Compounds in the R6B2C2Q14 Family

Four new deficient compounds in the R6B2C2QI4 family, LasCaSn2.75S4 1, Y6A10.67Ge2S14 2, Er5.33Si4S14 3 and Er4Ge4SI4 4, have been obtained via a precursor/flux method. Single-crystal analysis indicated that their crystal structures consist of three types of building blocks： RS7 （R = La/Ca for 1, R = Y for 2, R = Er for 3 and 4） mono-triangonal prism, CS6 （C = A1 for 1, C = Sn（2） for 2, C = Si（2） for 3, C = Ge（2） for 4） octahedron, and BS4 （B = Si for 1, B = Sn（1） for 2, B = Si（1） for 3, B = Ge（1） for 4） tetrahedron, as any other compounds belong to the R6B2C2Q14 family.     

From CsKTaF7 to CsNaTaF7: Alkali Metal Cations Regulation to Generate SHG Activity**

Inorganic metal halides play important roles in wide range of areas including fluorescence, X-ray detection, and nonlinear-optics. Herein, two new mixed alkali metal tantalum fluorides, CsKTaF₇ and CsNaTaF₇, have been obtained based on the strategy of cations regulation in A₂MF₇ (A represents monovalent cations and M is d⁰ transition-metal cation) system by a conventional hydrothermal route. CsKTaF₇ crystallizes in the centric Pnma space group, while CsNaTaF₇ crystallizes in the polar Cmc2₁ space group and exhibits moderate and phase-matchable NLO activity. Both halides possess large optical band gaps above 5.0 eV. The crystal structure evolution, optical properties, and detailed theory calculations of these two halides were elucidated in this work.     

Explorations of new types of second-order nonlinear optical materials in Cd(Zn)-VV-TeIV-O Systems

Solid-state reactions of zinc(II) or cadmium(II) oxide, V(2)O(5), and TeO(2) at high temperature led to two novel quaternary compounds, namely, Zn(3)V(2)TeO(10) and Cd(4)V(2)Te(3)O(15). The structure of Zn(3)V(2)TeO(10) is a complicated three-dimensional (3D) network constructed by the interconnection of ZnO(5), ZnO(6), VO(4), and TeO(4) polyhedra via corner- and edge-sharing. Cd(4)V(2)Te(3)O(15) with an acentric structure features a 3D network in which the cadmium tellurite layers are further interconnected by both "isolated" VO(4) tetrahedra and one-dimensional (1D) vanadium oxide helical chains. Cd(4)V(2)Te(3)O(15) displays a second harmonic generation (SHG) efficiency of about 1.4 times that of KH(2)PO(4) (KDP). Both compounds are direct band-gap semiconductors and are transparent in the range of 0.6-10.0 mum. Measurements of luminescence indicate that both compounds exhibit broad emission bands in the blue-light region.     

The structural properties of a noncentrosymmetric polymorph of 4‐aminobenzoic acid

The crystal structure of a polymorph of 4‐aminobenzoic acid (PABA), C₇H₇NO₂, at 100 K is noncentrosymmetric, as opposed to centrosymmetric in the structures of the other known polymorphs. The two crystallographically independent PABA molecules form pseudocentrosymmetric O—H...O hydrogen‐bonded dimers that are further linked by N—H...O hydrogen bonds into a three‐dimensional network. The benzene rings stack in the b direction. The CO₂ moieties are bent out slightly from the benzene ring plane.     

New Noncentrosymmetric Tetrel Pnictides Composed of Square-Planar Gold(I) with Peculiar Bonding

Three novel isostructural equiatomic gold tetrel pnictides, AuSiAs, AuGeP, and AuGeAs, were synthesized and characterized. These phases crystallize in the noncentrosymmetric (NCS) monoclinic space group Cc (no. 9), featuring square-planar Au within cis-[AuTt₂Pn₂] units (Tt=tetrel, Si, Ge; Pn=pnictogen, P, As). This is in drastic contrast to the structure of previously reported AuSiP, which exhibits typical linear coordination of Au with Si and P. Chemical bonding analysis through the electron localization function suggests covalent two-center two-electron Tt−Pn bonds, and three-center Au−Tt−Au and Au−Pn−Au bonds with 1.6 e⁻ per bond. X-ray photoelectron spectroscopy studies support the covalent and nonionic nature of Au−Pn and Au−Tt bonds. The title materials were found to be n-type narrow-gap semiconductors or semimetals, with nearly temperature-independent electrical resistivities and low thermal conductivities. A combination of the semimetallic properties with tunable NCS structure provides opportunities for the development of materials based on gold tetrel pnictides.