Syntheses and Crystal Structures of Two AlxRE3(Si1-yAly)S7(RE=Sm and Gd)Compounds

Two new quaternary rare-earth chalcogenides,Al_（0.42）Sm_3（Si_（0.74）Al_（0.26））S_7（1） and Al_（0.38）Gd_3（Si_（0.86）Al_（0.14））S_7（2）,have been synthesized by a facile solid-state route with boron as the reducing reagent.They crystallize in the noncentrosymmetric hexagonal space group P6_3,belonging to the Ce_6Al_（3.33）S_（14） structure-type.Their 3-D structures feature 3-D frameworks constructed by RES_8 bicapped trigonal prisms,and Al and Si occupy the octahedral and tetrahedral voids,respectively.Al（2） and Si（1） co-occupying the 2b site and Al（1） partially occupying the 2a site have to be considered for the stability of the structures and charge balances.The Ce_6Al_（3.33）S_（14） structure-type compounds with their rich compositions and traits are discussed.The diffuse reflectance spectrum measurement of 2 indicates that it has an energy gap of 2.13 eV.

Synthesis and Crystal Structure of Ho_4S_3Si_2O_7

In an attempt to synthesize the homologous sulfide of KHo2CuSe4 by using KBr as flux in a sealed evacuated quartz tube, transparent crystals of Ho4S3Si2O7 (Mr = 924.08) were isolated. The crystal structure of Ho4S3Si2O7 was determined by single-crystal X-ray diffraction method. Ho4S3Si2O7 crystallizes in a tetragonal system, space group I41/amd (No. 141) with a = 11.666(4), c = 13.593(5) ? V = 1850(2) ?, Z = 8, Dc = 6.64g/cm3, F(000)= 3200, m(MoKa) = 34.79mm-1, final R = 0.0355 and Rw = 0.0378 for 851 reflections with I > 3s(I). The structure of Ho4S3Si2O7 contains two crystallographically independent Ho3+ cations that are interconnected by S2 anions and the isolated [Si2O7]6 units. Ho(1) is coordinated by three O atoms and three S atoms to form a trigonal prismatic geometry, while Ho(2) is coordinated by six O atoms and three S atoms to form a tricapped trigonal prismatic geometry. The Si2O7 double tetrahedra are in the eclipsed configuration with non-linear SiOSi bridges (angle : 129.2(9)).

Synthesis and Single Crystal Structure of RbEr_2Cu_3Se_5

Single crystals of a new quaternary rare-earth selenide RbEr2Cu3Se5 have been isolated through the RbCl flux reaction in the RE-Cu-Se system. The title compound crystallizes in an orthorhombic system, space group Cmcm with a = 4.089(2), b = 14.498(6), c = 16.977(2) ? V = 1006.5(7) ?, Z = 4, Dc = 6.63 g/cm3, F(000) = 1720 and m(MoKa) = 45.51 mm-1. The final R = 0.0498 and wR = 0.0734 for 1401 observed reflections with I > 3s(I). The structure of RbEr2Cu3Se5 is a three-dimensional tunnel structure composed of ErSe6 and CuSe4 polyhedra with the charge-balanced Rb+ cations stuffing into the one-dimensional channels along the a direction. In the Er2RbCu3Se5 structure, the 1[Er2Se(1)4/2Se(2)2Se(3)4/2] double-octahedral chains are linked into a 2[Er2Cu2Se6] layer in the a-b plane via sharing Se(1)Se(3) edges with the 1[Cu(2)2Se(1)2Se(3)4/2] double tetrahedral chains, and 2[Er2Cu2Se6] layers are further interconnected along the c direction by sharing Se(1)Se(2) edges with the 1[Cu(1)Se(1)2Se(2)2/2] tetrahedral chains, forming a three-dimensional framework with the channels along the a axis accommodated by Rb+ ions.

Crystal Structure and Properties of a Sodium Terbium Borate Na_(2.67)Tb_(2.11)B_3O_9

A new nonlinear optical crystal of sodium terbium borate （Na2.67Tb2.11B3O9, Mr = 573.14） was synthesized by solid reaction method. The colorless transparent single crystals were grown from the high temperature solution by employing NaBO2 as flux. The structure was deter- mined by single-crystal X-ray diffraction method. The compound crystallizes in the orthorhombic system, space group Amm2 with a = 5.0744（10）, b = 10.990（2）, c = 6.9078（14） A, V = 385.24（13） A3, Dc = 4.941 g/cm3, F（000） = 250, Z = 2, μ= 9.205 mm-1, the final R = 0.0253 and wR = 0.0610. Its three-dimensional network structure is constructed from isolated BO33-, Na（1）O8, Na（2）O6, Na（3）O6 and Tb（1）O9 polyhedra. Variable-temperature magnetic susceptibility measurements show the compound is paramagnetic （μj = 7.04 μb）. The intensity of the second harmonic generation of Na2.67Tb2.11B3O9 is 2.5 times that of KDP.

Synthesis, Single-crystal Structure, and Optical and Magnetic Properties of CaEr_2S_4

Brown needle-like crystals of CaEr2S4 were isolated as the major product from a reaction of elements and binary sulfides by a two-step flux technique. CaEr2S4 crystallizes in the orthorhombic space group Pnma with a=12.845（4）, b=3.862（4）, c=13.001（2）（A）, V=645.0（7）（A）3,Z=4, F（000）=880,μ（MoKα）=27.794 mm^-1, the final R=0.0528 and wR=0.0562 for 1070observed reflections with I 〉 3σ（I）. The CaEr2S4 structure forms a three-dimensional framework that consists of interconnected tetra-octahedral Er4S18 fragments. Ca^2＋cations, in a monocapped trigonal prism geometry, are stuffed in two parallel rows into the one-dimensional channels along the b direction. CaEr2S4 is an infrared-transparent semiconductor with a band gap of 1.81 eV. Magnetic susceptibility measurements over 6～300 K indicate a Curie-Weiss paramagnetic behavior for the phase, with an effective magnetic moment of 9.64（1） μB per Er^3＋ ion.

Syntheses,Structures and Band Gaps of KLnSiS_4(Ln=Sm,Yb)

Two new quaternary sulfides, KSmSiS4 （1） and KYbSiS4 （2）, have been synthesized by high-temperature solid-state reaction. Single,crystal X-ray diffraction analyses indicate that both compounds crystallize in the space group P21/m, and the crystal data are as follows： a = 6.426（11）, b = 6.582（11）, c = 8.602（15）A, β= 107.90（13）°, Z = 2, V= 346.2（10） A^3, Dc = 3.317 g/cm^3, F（000） = 318,μ（MoKα） = 10.334 mm^-1, the final R = 0.0559 and wR = 0.1370 for 1; and α= 6.3244（10）, b = 6.5552（10）, c = 8.5701（15）A, β= 108.001（13）°, Z = 2, V = 337.91（9） A^3, De= 3.621 g/cm^3, F（000） = 334, μ（MoKα） = 15.737 mm^-1, the final R = 0.0422 and wR = 0.0960 for 2. The KLnSiS4 （Ln = Sm, Yb） structure consists of corrugated ∞^2 [LnSiS4]^- layers which are formed by edge-sharing LnS8 bicapped trigonal prisms and SiS4 tetrahedra. The K^＋ cations are located in the cavities defined by S2 anions between the ∞^2[LnSiS4]^- layers. Band-gap analyses show that compounds 1 and 2 are semiconductors with optical band-gaps of 2.40 and 2.34 eV, respectively.