Jinfan Huang

Synthesis, crystal structure, and optical properties of a new bismuth magnesium vanadate : BiMg2VO6

Abstract A new bismuth magnesium vanadate, BiMg 2 VO 6 , has been synthesized and structurally characterized from single crystal X-ray diffraction data. It crystallizes in orthorhombic symmetry with a = 7.9136(6) A, b = 12.246(2) A, c = 5.444(2) A, V = 527.6(2)A 3 , z = 4, and a space group of Cmcm (No. 63). An unusual fivefold coordination is found for Mg. The five O atoms bound to Mg form a square pyramidal coordination polyhedron with MgO bond lengths ranging from 1.973(7) to 2.066(3) A. The Bi atom is coordinated by four O atoms with BiO bond lengths 2.213(2) A forming a square pyramid. The V atom bonds to four O atoms with VO distances from 1.672(6) to 1.725(5) A; all the OVO angles are very close to the value of an ideal VO 4 tetrahedron. The BiMg 2 VO 6 structure may be viewed as connected chains of edge-shared BiO 4 units and corner-shared MgO 5 units extending along the c axis. These chains are then connected to each other through the VO 4 tetrahedra and edge sharing of the MgO 5 units. The absorption edge (about 450 nm) determined from the photothermal deflection technique is consistent with results from the excitation-emission spectrum. An emission band around 650 nm was observed. The IR spectrum of this compound is also reported.

The mixed orthoborate pyroborates Sr2Sc2B4O11 and Ba2Sc2B4O11: Pyroborate geometry

Abstract Two new alkaline-earth scandium borates, the mixed orthoborate pyroborates A 2 Sc 2 B 4 O 11 ( A = Sr or Ba), have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. The compounds may be represented by the descriptive formula A 2 Sc 2 (BO 3 ) 2 (B 2 O 5 ) which indicates two orthoborate groups and one pyroborate group for each formula unit. The Sr compound crystallizes in the triclinic system in space group P 1 (No. 2) with cell parameters a = 6.293(3), b = 7.285(3), c = 5.084(3) A, α = 90.71(5), β = 104.68(4), γ = 78.07(4)°, and V = 220.4(4) A 3 . The structure exhibits layers composed of an admixture of orthoborate and pyroborate groups. These layers are interleaved by Sr atoms occupying 8-coordinate sites and Sc atoms occupying distorted octahedral sites. The geometry of the pyroborate group is unusual, exhibiting the angle BOB = 180°. The Ba compound crystallizes in the monoclinic system in space group C2 c (No. 15) with cell parameters a = 16.022(2), b = 9.354(2), c = 6.343(2) A, β = 100.42(2)°, and V = 934.8(7) A 3 . The structure contains two types of Sc-centered, distorted octahedral sites. One type is isolated by bridging borate groups while members of the second type condense along trans edges to form one-dimensional chains. The chains are bridged by Ba atoms, simple orthoborate groups, and a unique pyroborate group. The principal planes of the pyroborate are rotated by 76.8°, one relative to the other, and the angle BOB = 112.1(7)°. Results of extended Huckel calculations indicate facile rotation of the principal planes of the pyroborate group is expected.

New layered copper oxides containing double CuO2 sheets: Ca3Cu2O4Cl2 and Ca3Cu2O4Br2

Two new compounds, Ca3Cu2O4Cl2 and Ca3Cu2O4Br2, have been synthesized. The x-ray powder patterns of these compounds indicate tetragonal crystal structures with a = 3.861(1) A and c = 21.349(6) A for Ca3Cu2O4Cl2 and a = 3.8651(2) A and c = 23.620(1) A for Ca3Cu2O4Br2. These structures are closely related to those of the known compounds of the type A2CuO2X2 where A may be Ca or Sr and X may be Cl or Br. Electrical and magnetic properties of the new phases were evaluated. These phases contain the CuO2 sheets which generally give high-temperature superconductivity when the copper oxidation state is suitably adjusted. However, attempts to dope both the A2CuO2X2 and A3Cu2O4X2 phases to produce superconductivity have been unsuccessful.

Crystal structure of high temperature strontium pyrovanadate

Abstract Single crystals of the high-temperature phase of strontium pyrovanadate, α-Sr 2 V 2 O 7 , were grown from a melt in the Bi-Sr-V-O system. This compound crystallizes in the triclinic system in space group P1 (#2) with α = 7.0936(4) A , b = 12.986(2) A , c = 7.046(1) A , α = 93.78(1)°, β = 90.877(7)°, γ = 99.447(7)°, V = 638.6(1) A 3 and Z = 4. The structure can be described as the packing of four Sr 2 V 2 O 7 layers that are approximately normal to the b axis or as the stacking of two zigzag chains. Two different types of (V 2 O 7 ) 4− anions are present. Three reported X-ray powder patterns are indexed with the cell parameters from this work. The α-to-β polymorphic transition temperature is about 645°C.

A new bismuth strontium vanadate, BiSr2V3O11, with both orthovanadate and pyrovanadate groups

Abstract A new bismuth strontium vanadate, BiSr2V3O11, has been synthesized, and its structure was determined from single crystal X-ray diffraction data. This compound may be represented by the descriptive formula BiSr2(VO4)(V2O7), indicating one orthovanadate group and one pyrovanadate group in each formula unit. The compound crystallizes in the triclinic space group P 1 with a = 7.0332(6) A, b = 10.213(2) A, c = 6.982(2) A, α = 96.01(2)°, β = 92.87(2)°, γ = 99.16(2)°, V = 491.3(1) A3, and Z = 2. The Bi atom is 7-coordinated to oxygen atoms with BiO distances from 2.208(8) to 2.88(1) A. Two types of Sr atoms were found: one with a coordination number of 9 and the other with one of 7. For the orthovanadate group, the average VO bond length is 1.72 A and the OVO angles are in the range of 103.9(4)° to 116.2(4)°. For the pyrovanadate group, the average VO bond length is 1.716 A and the VOV angle is 125.3°.

Synthesis and structure of new bismuth containing oxychlorides: BiSr3O3Cl3 and BiCa3O3Cl3

A new bismuth strontium oxychloride BiSr 3 O 3 Cl 3 has been synthesized and structurally characterized from single crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma (#62) with a =6.687(2) A, b =11.4618(8) A, c =11.565(2) A, V =886,4(3) A 3 , and Z =4. From the formula weight of 626.20, the density is calculated to be 4.693 g/cm 3 . The structure of BiSr 3 O 3 Cl 3 can be described as a layered structure arranged in sequence Cl/Sr-O/Bi-Sr-O-Cl/Sr-O/Cl along the b axis. The Bi-Sr-O-Cl layer is unique among all the known bismuth oxyhalides in that oxygen and halide are mixed in one layer. Two types of Sr atom and one type of Bi atom are found. Strontium of the Sr-O layer is coordinated by three O atoms with Sr-O distances ranging from 2.404(7) to 2.557(6) A and by five Cl atoms with Sr-Cl distances from 3.010(2) to 3.394(3) A. Strontium of the Bi-Sr-O-Cl layer is coordinated to three oxygen atoms with Sr-O distances in the range of 2.419(8) to 2.505(6) A and to six chlorine atoms with Sr-Cl distances in the range 2.922(3) to 3.796(4) A. The Bi atom is coordinated by three O atoms and two Cl atoms with Bi-O bond lengths ranging from 2.062(8) to 2.071(6) A and Bi-Cl bond lengths of 3.472(3) A. The isostructural compound BiCa 3 O 3 Cl 3 was also synthesized; the cell dimensions from single crystal data are a =6.383(3) A, b =10.803(3) A, and c =11.422(3) A.