Vertex-sharing Octahedra Research Articles

Crystal Structure and Magnetic Properties of the Novel Hollandite Ba1.3Co1.3Ti6.7O16

Single crystals of the new barium hollandite Ba1.3Co1.3Ti6.7O16 were obtained from a BaCl2 flux (I2/m, Z = 1, a = 9.9470(4), b = 2.9714(2), c = 10.2260(5) Å , β = 90.906(2)◦). In the crystal structure piles of Ba atoms are situated within a framework of edge- and vertex-sharing octahedra (Co,Ti)O6. The composition was deduced from microprobe analyses, structure refinements and charge balance arguments in agreement with the observed magnetic properties. The temperature dependence of the magnetic susceptibility χ(T) of Ba1.3Co1.3Ti6.7O16 single crystals reveals paramagnetism down to 2 K. The value of the Co magnetic moment deduced from the Curie-Weiss law agrees well with the theoretical value of the high-spin state spin-only moment of μeff = 3.87 μB for Co2+ (S = 3/2)

A New Perovskite Polytype in the High-Pressure Sequence of BaIrO3

The high-pressure sequence of the perovskite polytypes of BaIrO(3) has been investigated in the pressure range up to 10 GPa. At ambient pressure the so-called "9R" polytype has been prepared by solid-state reaction and slow cooling in air to yield an almost fully oxygen-stoichiometric BaIrO(2.96(1)) composition. The crystal structure has been refined from XRD data in the monoclinic C2/m space group with a = 10.0046(3) A, b = 5.75362(14) A, c = 15.1839(4) A, beta = 103.27(1) degrees ; it contains trimers of face-sharing octahedra (or Ir(3)O(12) trioctahedra) that are linked by their vertices to form columns parallel to the c-axis with a stacking of layers of corner sharing (c) and face sharing (h) IrO(6) octahedra along the sequence hhchhc. This structure is stable up to 3 GPa; at 4 GPa a new 5H polytype has been stabilized as a pure phase. The crystal structure has been solved by ab initio procedures from powder XRD data. It is monoclinic with a = 9.9511(2) A, b = 5.7503(1) A, c = 13.71003(3) A, beta = 118.404(2) degrees , and it was refined in the C2/m space group from NPD data collected at room temperature. This polytype can be described as a stacking of IrO(6) octahedra along the sequence hchcc. The structure contains chains of double dimer units of face-sharing octahedra; the twin dimers are connected to single layers of vertex-sharing octahedra, forming infinite chains along c. This is a unique stacking that, with this repetition length, has never been described before among the hexagonal polytypes of ABO(3) perovskites. The 5H polytype is stable in a narrow pressure range; at 5 GPa the 6H structure is formed, stable up to 10 GPa. The 6H-BaIrO(3) polytype is monoclinic, space group C2/c, with a = 5.7483(2) A, b = 9.9390(3) A, c = 14.3582(5) A, beta = 91.319(2) degrees . The structure consists of dimers of face-sharing octahedra separated by single corner-sharing octahedra, showing the sequence hcchcc along the c-axis. At 10 GPa the cubic 3C perovskite structure could be identified as a minority phase, with a = 4.0611(7) A, defined in the Pm3m space group. The precarious stability of the 5H polytype, as well as the novel pressure sequence displayed by BaIrO(3) that is distinct from the classical sequence 9R-4H-6H-3C exhibited by many transition metal oxides, for instance BaRuO(3), is a result of the particular stability of the "9R" ambient-pressure structure, which is reinforced by a strong Ir-Ir bond across the octahedral faces, and the Ir-Ir Coulombic repulsion across shared faces that destabilizes the 4H polytype relative to the 6H phase to allow stabilization of the hybrid 5H polytype in a narrow presure range.

(A19N7)[In4]2 (A: Ca, Sr) and (Ca4N)[In2]: Synthesis, Crystal Structures, Physical Properties, and Chemical Bonding.

AbstractFor Abstract see ChemInform Abstract in Full Text.

NEVADAITE, (Cu2+, , Al, V3+)6 [Al8 (PO4)8 F8] (OH)2 (H2O)22, A NEW PHOSPHATE MINERAL SPECIES FROM THE GOLD QUARRY MINE, CARLIN, EUREKA COUNTY, NEVADA: DESCRIPTION AND CRYSTAL STRUCTURE

Nevadaite, (Cu 2+ , □, Al, V 3+ ) 6 (PO 4 ) 8 F 8 (OH) 2 (H 2 O) 22 , is a new supergene mineral species from the Gold Quarry mine, near Carlin, Eureka County, Nevada, U.S.A. Nevadaite forms radiating clusters to 1 mm of prismatic crystals, locally covering surfaces more that 2 cm across; individual crystals are elongate on [001] with a length:width ratio of >10:1 and a maximum diameter of ~30 μm. It also occurs as spherules and druses associated with colorless to purple-black fluellite, colorless wavellite, strengite–variscite, acicular maroon-to-red hewettite, and rare anatase, kazakhstanite, tinticite, leucophosphite, torbernite and tyuyamunite. Nevadaite is pale green to turquoise blue with a pale powder-blue streak and a vitreous luster; it does not fluoresce under ultraviolet light. It has no cleavage, a Mohs hardness of ~3, is brittle with a conchoidal fracture, and has measured and calculated densities of 2.54 and 2.55 g/cm 3 , respectively. Nevadaite is biaxial negative, with α 1.540, β 1.548, γ 1.553, 2 V (obs.) = 76°, 2 V (calc.) = 76°, pleochroic with X pale greenish blue, Y very pale greenish blue, Z blue, and with absorption Z ≫ X > Y and orientation X = c , Y = a , Z = b. Nevadaite is orthorhombic, space group P 2 1 mn , a 12.123(2), b 18.999(2), c 4.961(1) A, V 1142.8(2) A 3 , Z = 1, a:b:c = 0.6391:1:0.2611. The strongest seven lines in the X-ray powder-diffraction pattern [ d in A(I)( hkl )] are: 6.077(10)(200), 5.618(9)(130), 9.535(8)(020), 2.983(6)(241), 3.430(4)(041), 2.661(4)(061), and 1.844(4)(352). A chemical analysis with an electron microprobe gave P 2 O 5 32.54, Al 2 O 3 27.07, V 2 O 3 4.24, Fe 2 O 3 0.07, CuO 9.24, ZnO 0.11, F 9.22, H 2 O (calc.) 23.48, OH ≡ F–3.88, sum 102.09 wt.%; the valence states of V and Fe, and the amount of H 2 O, were determined by crystal-structure analysis. The resulting empirical formula on the basis of 63.65 anions (including 21.65 H 2 O pfu ) is (Cu 2.00 2+ Zn 0.02 V 0.98 3+ Fe 0.01 3+ Al 1.15 ) ∑ 4.16 Al 8 P 7.90 O 32 [F 8.37 (OH) 1.63 ] ∑10 (H 2 O) 21.65 . The crystal structure of nevadaite was solved by direct methods and refined to an R index of 4.0% based on 1307 observed reflections collected on a four-circle diffractometer with Mo K α X-radiation. The structure consists of ordered layers of vertex-sharing octahedra and tetrahedra alternating with layers of disordered vertex-sharing and face-sharing octahedra in the b direction. [Alϕ 5 ] chains of octahedra are decorated by (PO 4 ) tetrahedra that share vertices with octahedra adjacent in the chain. These chains link in the c direction by sharing vertices between octahedra and tetrahedra to form an ordered layer of the form [Al 8 (PO 4 ) 8 F 8 (H 2 O) 8 ]. In the disordered layer, octahedral containing positionally disordered Cu 2+ , V 3+ , Al and □ (vacancy) share trans faces to form columns that link by sharing octahedron vertices to form ribbons extending in the c direction; the resulting layer has the form {(Cu 2 2+ □ 2 V 3+ ,Al) ∑6 (H 2 O) 12 (OH) 2 (H 2 O) x }, x ≈ 2. The layers link in the b direction by sharing vertices between octahedra and tetrahedra. Although decorated chains topologically equivalent to that in nevadaite are common in many oxysalt minerals, its chain is geometrically distinct from those topologically equivalent chains. The M – M linkage along the [ M ϕ 5 ] chains in most minerals take place through trans vertices of the octahedra, with one example of linkage through cis vertices; in nevadaite, the M – M linkage involves both trans and cis vertices, as does the chain in slavikite. In most of these decorated chains, alternate tetrahedra along the chain occur either in a trans or a cis arrangement. In nevadaite and slavikite, the tetrahedra are arranged in both trans and cis arrangements; the arrangements in these two minerals are geometrically distinct, however.

Hydrated metal complexes of N-(6-amino-3,4-dihydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl)glycinate: interplay of molecular, molecular-electronic and supramolecular structures.

The title anion, (C(7)H(8)N(5)O(4))(-), L(-), forms hydrated metal complexes with a range of metal ions M(+) and M(2+). Lithium and manganese(II) form finite molecular aggregates [Li(L)(H(2)O)(3)] (1) and [Mn(L)(2)(H(2)O)(4)].6H(2)O (4) in which the molecular aggregates are linked into three-dimensional frameworks by extensive hydrogen bonding. The sodium and potassium derivatives, [Na(2)(L)(2)(H(2)O)(3)] (2) and [K(L)(H(2)O)] (3) both form organic-inorganic hybrid sheets in which metal-oxygen ribbons are linked by strips containing only organic ligands: these sheets are linked by hydrogen bonds into three-dimensional frameworks. In (2) the metal-oxygen ribbon is built from pairs of edge-shared trigonal bipyramids linked by water molecules, while in (3) it consists of a continuous chain of vertex-sharing octahedra. The nitroso group in the anion acts as an eta(1) ligand towards Na(+) and as an eta(2) ligand towards K(+). In all cases the anion L(-) shows the same unusual pattern of interatomic distances as the neutral parent LH.

Synthesis and Crystal Structures of α- and β-CsTi 3P 5O 19

Crystals of α-CsTi 3P 5O 19, the low temperature phase, and β-CsTi 3P 5O 19, the high temperature phase, have been obtained by flux growth methods and structurally characterized by single crystal X-ray diffraction techniques. Crystal data: α-CsTi 3P 5O 19, monoclinic, Cm , a = 9.309(2) Å, b = 14.081(3) Å, c = 6.314(1) Å, β = 105.82(3)°, V = 796.3 Å 3 Z = 2, R = 0.027 for 928 unique reflections; β-CsTi 3P 5O 19, monoclinic, C 2/ c, a = 10.987(1) Å, b = 16.588(1) Å, c = 8.7618(8) Å, β = 100.09(1)°, V = 1572.2 Å 3, Z = 4, R = 0.038 for 1678 unique reflections. The two polymorphs have different three-dimensional networks of vertex-sharing octahedra and tetraheda. The framework of the α-phase consists of dimers of corner-sharing TiO 6 octahedra and discrete TiO 6 octahedra joined through PO 4 tetrahedra and P 2O 7 groups by corner-sharing. The β-phase is built up from discrete TiO 6 octahedra, PO 4 tetrahedra, and P 2O 7 groups. The structural formulas are CsTi(Ti 2O)(PO 4)(P 2O 7) 2 and CsTi 3(PO 4) 3(P 2O 7) for the α- and β-phases, respectively. Both frameworks have tunnels where the cesium cations are located. The cesium cations in the β-phase are disordered.

Structural and Electronic Properties of the Mixed Co/Ru Perovskites AA′CoRuO 6 ( A, A′ = Sr, Ba, La)

The compounds Sr 2CoRuO 6, SrLaCoRuO 6, Ba 2CoRuO 6, and BaLaCoRuO 6 have been prepared and characterized by X ray powder diffraction and SQUID magnetometry. All but Ba 2CoRuO 6 crystallize as pseudo-cubic perovskites with a disordered arrangement of Co and Ru cations over the six-coordinate sites. Ba 2CoRuO 6 adopts the hexagonal 6H perovskite structure with Co in the vertex-sharing octahedra and a random arrangement of Co and Ru in the M 2O 9 dimers. Frustration is apparent in the magnetic properties of each of these compounds at low temperatures, in contrast to the 6H perovskite Ba 3CoRu 2O 9, which shows no structural disorder and orders antiferromagnetically at 106 K.

The magnetic properties of the frustrated bidimensional antiferromagnet CsBaFe 3F 12

CsBaFe 3F 12 is isostructural with CsBaCr 3F 12 (monoclinic, C2/c, cell parameters at 130 K: a = 17.402(2) A ̊ , b = 9.994(1) A ̊ . c = 14.928(2) A ̊ , β = 124.76(2) δ, Z = 4). The structure is built up from [Fe 3F 12] layers of vertex-sharing octahedra separated by cesium and barium ions. The magnetic susceptibility measurements show an antiferromagnetic behaviour below the Néel temperature ( T N = (55±2)K) accurately determined by Mössbauer spectroscopy. The first calculated simulations of the magnetic structure give evidence for a magnetic cell ( a,3 b, c) with a 120° rotation angle of the spins which corresponds to a frustrated magnetic configuration.

Mixed [formula omitted] oxides: The crystal structure of Ba 3NiRuSbO 9

The crystal structure of Ba 3NiRuSbO 9 has been refined by Rietveld analysis of neutron powder diffraction data: space group P6 3 mmc , a = 5.7856(3), c = 14.2321(4) A ̊ at 295K. The phase adopts a 6H-BaTiO 3-like structure, with Ni 2+ exclusively occupying the vertex-sharing octahedra and a random distribution of Ru 5+ Sb 5+ on the face sharing sites. A magnetic susceptibility study shows that Ba 3NiRuSbO 9 follows an approximate Curie-Weiss law ( μ av = 3.50 μ B, υ = −25 K) down to 80 K, though a slight deviation from linearity at lower temperatures is indicative of some short-range magnetic order.

Crystal chemistry, plane nets and arabic mosaics: the structure of CsBaCr3F12, a new MX4 network

Abstract CsBaCr3F12 is monoclinic (S.G.: C2/c): a = 17.184(4) Å, b = 9.886(2) Å, c = 15.037(5) Å, β = 124.32(2)°, Z = 8. The structure was solved from single crystal data using 2218 independent reflections (R = 0.053, Rw = 0.042). The structure is built up from [Cr3F12] layers of vertex-sharing octahedra separated by cesium and barium ions located in an ordered way. The topology of the layers is unique and illustrates a case of plane net predicted by O'Keeffe, yet unknown in nature but imaginated by arabic artists in the 18th century.