The crystal structure of Cs[VOF3] · 12H2O

The crystal structure of $\text{Cs[VOF}{}_3\text{]}\text{·}\text{1}\text{2}\text{H}{}_2\text{O}$ has been determined and refined on the basis of three-dimensional X-ray diffractometer data (MoKα radiation). The structure is monoclinic, a = 7.710(2), b = 19.474(7), c = 7.216(2)Å, β = 116.75(1)°, V = 967.5ų, Z =8, space group Cc (No. 9). The final R and R_w were 0.0295 and 0.0300, respectively, for 1356 independent reflections and 117 variables.The structure contains two crystallographically different VOF₅ octahedra linked so as to form complex chains. Two non-equivalent octahedra share one FF edge, forming V₂O₂F₈ doublets. Two F atoms, connected to different V atoms within the doublet, form an edge in the adjacent equivalent V₂O₂F₈ unit thus continuing the chain. The VO distances are 1.583(7) and 1.595(7) Å. The VF distances are in the range 1.881-2.205 Å, mean value: 1.989 Å. The H₂O group is a crystal water molecule.     

La3Os2O10, a new compound containing isolated clusters Os2O10 with metal-metal bonds

The formula of a new compound isolated in the LaOsO system has been established by means of crystal structure determination. There are two La₃Os₂O₁₀ units in a face-centered monoclinic unit cell (S.G. $\text{C2}\text{m}$); a = 7.911(2) Å, b = 7.963(2) Å, c = 6.966(2)Å, β = 115.76(2)°;. For 1082 intensities, collected on an automated single-crystal diffractometer, the final R value was 0.025 after absorption corrections. The structure consists of isolated Os₂O₁₀ clusters composed of two edge-shared OsO₆ octahedra. These dimeric units are connected together by two types of La³⁺ ions in eightfold coordination. In view of the OsOs distance inside the pair (2.462 Å), La₃Os₂O₁₀ provides an example of metal-metal bonding involving a transition metal in a half-integral formal oxidation state of 5.5.     

L'oxyde double TeVO4 II. Structure cristalline de TeVO4-β-relations structurales

β-TeVO₄ crystallizes in the monoclinic system with the space group $\text{P2}{}_1\text{c}$ and the parameters: a = 4.379 Å, b = 13.502 Å, c = 5.446 Å, and β = 91.72°. Vanadium occupies the center of a square pyramid of oxygens, an extra oxygen is at VO = 2.77 Å. These distorted octahedra share corners forming puckered sheets parallel to (010). The sheets are held together by [Te₂O₆]^4? groups in which tellurium is one-side coordinated by four oxygen atoms.     

Oxydes de plomb. I. Structure cristalline du minium Pb3O4, à température ambiante (293 K)

The structure of Pb₃O₄ at 293 K has been refined to an R value of 0.06, using 29 neutron diffraction data obtained from a powdered sample.Oxygen atoms are displaced in the quadratic cell (space group $\text{P4}{}_2\text{mbc}\text{; a = 8.811}$ Å and c = 6.563 Å) with respect to previous results obtained by several authors. The interatomic Pb^IVO and Pb^IIO distances are compared with those found in other lead oxides. While the oxygen octahedra around Pb^IV atoms are characterized by bondings a little too long, the divalent lead coordination is characterized by bondings a little too short.     

The crystal structure of Ba2V2O7

Ba₂V₂O₇ is triclinic with a = 13.571(3), b = 7.320(2), c = 7.306(2) Å, α = 90.09(1), β = 99.48(1), β = 99.48(1), γ = 87.32(1)°, V = 7.15.1 ų, Z = 4, and space group $\text{P}\text{1}$. The crystal structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares analysis to a R_w of 0.034 (R = 0.034) using 2484 reflections measured on a Syntex $\text{P}\text{1}$ automatic four-circle diffractometer. The structure has two unique divanadate groups that are repeated by the b and c lattice translations to form sheets of divanadate groups parallel to (100). These sheets are linked by four unique Ba atoms that lie between these sheets. Ba(1) and Ba(3) are coordinated by eight oxygens arranged in a distorted biaugmented triangular prism and a distorted cubic antiprism, respectively. Ba(2) is coordinated by 10 oxygens arranged in a distorted gyroelongated square dipyramid and Ba(4) is coordinated by nine oxygens arranged in a distorted triaugmented triangular prism. These coordination numbers are substantiated by a bond strength analysis of the structure, and the variation in 〈BaO〉 distances is compatible with the assigned cation and anion coordination numbers. Both divanadate groups are in the eclipsed configuraton with 〈VO(br)〉 bond lengths of 1.821(4) and 1.824(4) Å and VO(br)V angles of 125.6(3) and 123.7(3)°, respectively. Examination of the divanadate groups in a series of structures allows certain generalizations to be made. Longer 〈VO(br)〉 bond lengths are generally associated with smaller VO(br)V angles. When VO(br)V < 140°, the divanadate group is generally in an eclipsed configuration; when VO(br)V > 140°, the divanadate group is generally in a staggered configuration. Nontetrahedral cations with large coordination numbers require more oxygens with which to bond, and hence O(br) is more likely to be three coordinate, with the divanadate group in the eclipsed configuration. In the eclipsed configuration, decrease in VO(br)V promotes bonding between O(br) and nontetrahedral cations, and hence smaller nontetrahedral cations are generally associated with smaller VO(br)V angles.     

Phase equilibria in the system V2O3Ti2O3TiO2 at 1473°K

The phase equilibria in the V₂O₃Ti₂O₃TiO₂ system have been determined at 1473°K by the quench method, using both sealed tubes and controlled gaseous buffers. For the latter, $\text{CO}{}_2\text{H}{}_2$ mixtures were used to vary the oxygen fugacity between 10^?10.50 and 10^?16.73 atm. Under these conditions the equilibrium phases are: a sesquioxide solid solution between V₂O₃ and Ti₂O₃ with complete solid solubility and an upper stoichiometry limit of (V, Ti)₂O_3.02; an M₃O₅ series which has the V₃O₅ type structure between V₂TiO₅ and V_0.69Ti_2.31O₅ and the monoclinic pseudobrookite structure between V_0.42Ti_2.58O₅ and Ti₃O₅; series of Magneli phases, V₂Ti_n?2O_2n?1Ti_nO_2n?1, n = 4–8; and reduced rutile phases (V, Ti)O_2?x, where the lower limit for x is a function of the $\text{V}\text{(V + Ti)}$ ratio. The extent of the different solid solution areas and the location of the oxygen isobars have been determined.     

Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

The crystal structure of V_0.985Al_0.015O₂ has been refined from single-crystal X-ray data at four temperatures. At 373°K it has the tetragonal rutile structure. At 323°K, which is below the first metal-insulator transition, it has the monoclinic M₂ structure, where half of the vanadium atoms are paired with alternating short (2.540 Å) and long (3.261 Å) V-V separations. The other half of the vanadium atoms form equally spaced (2.935 Å) zigzag V chains. At 298°K, which is below the second electric and magnetic transition, V_0.985Al_0.015O₂ has the triclinic T structure where both vanadium chains contain V-V bonds, V(1)-V(1) = 2.547 Å and V(2)-V(2) = 2.819 Å. At 173°K the pairing of the V(1) chain remains constant: V(1)-V(1) = 2.545 Å, whereas that of the V(2) chain decreases: V(2)-V(2) = 2.747 Å. From the variation of the lattice parameters as a function of temperature it seems that these two short V-V distances will not become equal at lower temperatures. The effective charges as calculated from the bond strengths at 298 and 173°K show that a cation disproportionation has taken place between these two temperatures. About 20% of the V⁴⁺ cations of the V(1) chains have become V³⁺ and correspondingly 20% of the V⁴⁺ cations of the V(2) chains have become V⁵⁺. This disproportionation process would explain the difference between the two short V-V distances. Also it would explain why the T → M₁ transition does not take at lower temperatures.     

Röntgenographische,thermoelektrische, und IR-spektroskopische Untersuchung des Spinellsystems LixMn1−xV2O4

The spinels of the system Li_xMn_1?xV₂O₄ (0 ? x ? 1) have been prepared at 700–750°C from LiV₂O₄ and MnV₂O₄. The lattice constants decrease linearly with increasing x. In the region x>0.75, the d-electrons of V should be delocalized as the VV distances are lower than the critical VV separation of 2.94 Å. Experimentally, the samples with x>0.6 show no IR absorption bands and the Seebeck coefficient is near zero. The Seebeck coefficient can be described with a model of intermediate polarons and can be expressed by the equation $\text{Θ = 198}\text{log}\text{[1 +}\text{(1 ? x)}{}^5\text{x}\text{]}$.     

Phase diagram and some physical properties of V2O3+x1 (0 ? x ? 0.080)

The magnetic and electric properties of V₂O_3+x were investigated by measurements of magnetic susceptibility, electrical resistivity, magnetotorque, Mössbauer of doped ⁵⁷Fe, and NMR of ⁵¹V, and the results were compared with those of the (V_1?xTi_x)₂O₃ system or highly pressured V₂O₃. The results obtained are as follows: (1) The metallic state shows an antiferromagnetic ordering at T_N (x). The value of T_N for metallic V₂O₃, obtained by interpolation to x = 0, shows the coincidence between V₂O_3+x and the (V_1?xTi_x)₂O₃ system. (2) Magnetic susceptibility of V₂O_3+x is expressed as χ_M(V₂O_3+x) = (1?x)χ_M(V³⁺) + xχ_M(V⁴⁺). χ_M(V⁴⁺) obeys the Curie-Weiss law $\text{(χ}{}_{\mathrm{<mtext>M</mtext>}}\text{(}\text{V}{}^{\mathrm{4+}}\text{) =}\text{0.77}\text{T}\text{+ 17)}$. (3) In the insulating phase, the electrical resistivity ? is expressed as a common equation: $\text{? = 10}{}^{\mathrm{?1.8}}\text{exp}\text{(}\text{E}\text{kT}\text{)}$. This implies that the substitution of Ti or nonstoichiometry (V⁺⁴ + metal vacancies) has little influence on the carrier mobility (or bandwidth). (4) There is a critical length in the c-axis (? 14.01 Å) where the metal-insulator transition takes place. This suggests that the length of the c-axis plays an important role in the metal-insulator transition of V₂O₃-related compounds.     

A structural model for barium platinum oxide,Ba3Pt2O7

A single crystal study of Ba₃Pt₂O₇ shows that the structure tolerates a variable composition which can be written Ba₃Pt_2+xO_7+2x. The crystal studied has a hexagonal cell of dimensions a = 10.108 ± 0.006 Å and c = 8.638 ± 0.009 Å, and a probable space group $\text{P}\text{6}\text{2c, Z = 4}$. The density determined by water displacement is 7.99 g/cm³; the theoretical density for Ba₃Pt₂O₇ is 7.94 g/cm³. The structure was determined from the set of 401 observed independent reflections obtained from 5189 reflections measured by automated counter methods. Refinement on F was carried to a conventional R of 8.0%. The structure has barium-oxygen layers with an essentially four-layer stacking sequence of the double hexagonal (ABAB) type. Platinum is found mainly in face-sharing octahedra, but is also distributed over some sites in which the coordination is nearly square planar and other sites in which the coordination is trigonal prismatic with three PtO bond lengths of 2.00 Å and three long PtO distances of 2.65 Å. The platinum with planar coordination is 0.08 Å from the plane of the four oxygen atoms.     

Structural aspects of the metal-insulator transitions in (Ti0.9975V0.0025)4O7

The structure of (Ti_0.9975V_0.0025)₄O₇ has been refined at 298, 135, and 100°K from single-crystal X-ray diffraction data. This sample belongs to the region of the $\text{Ti}{}_4\text{O}{}_7\text{V}{}_4\text{O}{}_7$ phase diagram where still two electrical transitions are observed. The three structures of the V-doped sample are almost identical to the corresponding structures of pure Ti₄O₇. The charges are disordered in the metallic phase, they order very slightly in the intermediate phase, and they are almost completely ordered along the 3113 and the 4224 chains in the low-temperature phase. There is no evidence of cation pair-bond formation in the intermediate phase, whereas the Ti³⁺ cations are all paired in the low-temperature phase. The cationic Debye-Waller factors in the intermediate phase are anomalously large, which is indicative of a disorder. Thus, in order to explain the physical properties of the intermediate phase, as in the case of the pure sample, all the Ti³⁺ cations are thought to form pair bonds with no long-range order. The TiTi distances along the pseudorutile c-axis are shorter in the V-doped sample than in the pure one. This indicates that the relative bond strengths increase with the incorporation of vanadium. The main difference between pure Ti₄O₇ and (Ti_0.9975V_0.0025)₄O₇ is in the lattice parameters and unit-cell volume variations with temperature. In the latter sample two discontinuities are observed, each corresponding to one transition, whereas in the former only one transition is observed, which corresponds to the higher transition. In the low-temperature phase the V cations are either 3+ or 4+ and are either on the 3113 chains or on the 4224 chains. The V doping gives rise to four different patterns. Each one is discussed in order to explain the differences between V-doped sample and pure Ti₄O₇.     

Synthesis,characterization, and crystal structure of a new truly one-dimensional compound: PV2S10

PV₂S₁₀ was obtained by heating the elements in stoichiometric proportions at 490°C in evacuated Pyrex tubes. The crystal symmetry is monoclinic, space group $\text{P2}{}_1\text{c}$, with the unit cell parameters a = 12.734(8)Å, b = 7.349(7)Å, c = 23.662(4)Å, β = 95°22(1), V = 2205(4)ų, and Z = 8. The structure was solved from 2269 independant reflexions, and anisotropic least squares refinement gave R = 0.036 with 236 variables. The structure can be described as made of [V₂S₁₂] units forming endless chains themselves linked, two by two, by [PS₄] tetrahedra. In these units each vanadium is surrounded by eight sulfur atoms (mean d_VS = 2.459Å) arranged in a distorted bicapped triangular prism. Two of these prisms shared a rectangular face to form [V₂S₁₂] groups, in which intercationic distances implied vanadium-vanadium bonds (mean d_VV = 2.852(2)Å). Between the infinite double chains, only SS weak van der Waals' bonds exist. More than two thirds of the sulfur atoms are present as [SS]^?II pairs, (mean d_SS = 2.015Å); the rest are S^?II anions.     

Structural studies in the Li2MoO4MoO3 system: Part 1 the low temperature form of lithium tetramolybdate,LLi2Mo4O13

LLi₂Mo₄o₁₃ crystallizes in the triclinic system with unit-cell dimensions a = 8.578 Å, b = 11.450 Å, c = 8.225 Å, α = 109.24°, β = 96.04°, γ = 95.95° and space group $\text{P}\text{1}\text{, Z = 3}$. The calculated and measured densities are 4.02 g/cm³ and 4.1 g/cm³ respectively. The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 2468 unique reflections collected by counter methods, 1813 with I ? 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.031 (ωR = 0.038). LLi₂Mo₄O₁₃ is a derivative of the V₆O₁₃ structure with oxygen ions arranged in a face-centred cubic type array with octahedrally coordinated molybdenum and lithium ions ordered into layers.     

Idle spin behavior of the shifted hexagonal tungsten bronze type compounds FeIIFeIII2F8(H2O)2 and MnFe2F8(H2O)2

Fe^IIFe^III₂F₈(H₂O)₂ and MnFe₂F₈(H₂O)₂, grown by hydrothermal synthesis ($\text{P ? 200}\text{MPa}\text{, T = 450}\text{or}\text{380°}\text{C}$), crystallize in the monoclinic system with cell dimensions (Å): a = 7.609(5), b = 7.514(6), c = 7.453(4), β = 118.21(3)°; and a = 7.589(6), b = 7.503(8), c = 7.449(5), β = 118.06(3)°, and space group $\text{C2}\text{m}\text{, Z = 2}$. The structure is related to that of $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$. It is described in terms of perovskite type layers of Fe³⁺ octahedra separated by Fe²⁺ or Mn²⁺ octahedra, or in terms of shifted hexagonal bronze type layers. Both compounds present a weak ferromagnetism below T_N (157 and 156 K, respectively). Mössbauer spectroscopy points to an “idle spin” behavior for Fe^IIFe^III₂F₈(H₂O)₂: only Fe³⁺ spins order at T_N, while the Fe²⁺ spins remain paramagnetic between 157 and 35 K. Below 35 K, the hyperfine magnetic field at the Fe²⁺ nuclei is very weak: H_hf = 47 kOe at T = 4.2 K. For MnFe₂F₈(H₂O)₂, Mn²⁺ spin disorder is expected at 4.2 K. This “idle spin” behavior is due to magnetic frustration.     

Semiconductor-metal transitions in NbO2 and Nb1−xVxO2

NbO₂, Nb_0.98V_0.02O₂, and Nb_0.95V_0.05O₂ transform from semiconducting to metallic state at temperatures higher than the DTA phase-transition temperatures. Vibrational mode softening and c-axis NbNb pairing appear to be important factors in the mechanism of these transitions. In the solid solutions, $\text{c}\text{a}$ ratio is maximum at x = 0.5 since the metal-metal interaction along the c axis becomes minimum; conductivity is minimum at this composition since there are no mobile electrons.     

The structure of a barium niobium silicon oxide with the probable composition Ba6+xNb14Si4O47 (x ⋍ 0.23)

Reaction of BaO, Nb₂O₅, and Nb in mole ratios of 2.4:1.6:1 in an evacuated silica capsule at 1250°C produces a mixture of at least two products, one of which has the probable composition $\text{Ba}{}_{\mathrm{6+x}}\text{Nb}{}_{14}\text{Si}{}_4\text{O}{}_{47}\text{(x ? 0.23)}$. This compound has an hexagonal unit cell of dimensions a = 9,034 ± 0.004 Å, c = 27.81 ± 0.02 Å, probable space group $\text{P6}{}_3\text{mcm}\text{, Z = 2}$. Its structure has been determined from 942 independent reflections collected by a counter technique and refined by least squares methods to a conventional R value of 0.062. The basic structure consists of strings of four NbO₆ octahedra sharing opposite corners, each string joined to the next by edge sharing of the end octahedra, so that the c axis corresponds to the length of a strand of seven corner-linked octahedra. Chains of three such strands are formed by corner sharing between the strands. The chains in turn are joined by NbO₆ octahedra and Si₂O₇ groups in which the SiOSi linkage is linear. Barium atoms are in sites between the chains coordinated by 13 oxygen atoms. A second site, 15 coordinated, probably has a small amount of barium as well; the fractional occupancy for barium in this site is 0.076.     

The isotropic temperature factors of Sr(Co1−xMnx)O3 (x = 0, 0.1, 0.5, 0.8, and 1.0)

The cubic perovskite Sr(Co_1?xMn_x)O₃ has a maximum value of a-axis at x = 0.3 and a change of spin state of Co⁴⁺ ion from low to high. To elucidate these properties, the isotropic temperature factor (B) of strontium, cobalt, manganese, and oxygen atoms for x = 0, 0.1, 0.5, 0.8, and 0.1 have been derived from powder X-ray diffraction measurements. The isotropic temperature factor of oxygen for x = 0, 0.1, and 1.0 is small and that for x = 0.5 and 0.8 is large. This fact suggests that the oxygen ion deviates from the center of the CoOMn bond in the solid solutions with $\text{x ≧ 0.3}$. Larger CoO₆ octahedra and smaller MnO₆ octahedra, which are connected by corner sharing of oxygens of the octahedron, are distributed statistically.     

Interactions magnétiques dans des groupements binucléaires [Fe2O7]8− au sein de Na8Fe2O7

The magnetic interaction in the structural units [Fe₂O₇]^8?, built of two corner-sharing FeO₄ tetrahedra, in Na₈Fe₂O₇ ($\text{Na}{}_2\text{O}\text{Fe}{}_2\text{O}{}_3\text{=}\text{4}\text{1}$) has been studied by magnetic susceptibility measurements (4.2–500 K). An exchange integral $\text{J}\text{K}{}_{\mathrm{<mtext>B</mtext>}}$ of ?37 K is obtained by comparison of the experimental values and the calculated ones using a Heisenberg-Dirac-Van Vleck-type Hamiltonian ? = $\text{?2J}\text{S}\text{?}{}_1\text{S}\text{?}{}_2$. The hypothesis of magnetically isolated [Fe₂O₇]^8? groups is corroborated by Mössbauer spectroscopy between 1.5 and 77 K. The susceptibility measurements of the solid solutions Na₈Fe_2?xM_xO₇ (M = Al, Ga; 0 ≤ x ≤ 0.2 for Al; 0 ≤ x ≤ 2 for Ga) leads to the same conclusion of the existence of isolated Fe³⁺Fe³⁺ pairs in Na₈Fe₂O₇. The type of substitution of Fe by Al or Ga is determined; homonuclear Fe³⁺Fe³⁺ and M³⁺M³⁺ pairs and heteronuclear Fe³⁺M³⁺ pairs are formed.     

Structure cristalline du tétramétaphosphate de nickel-ammonium heptahydraté: Ni(NH4)2P4O12 · 7H2O

Nickel-ammonium tetrametaphosphate, Ni(NH₄)₂P₄O₁₂ · 7H₂O is triclinic with a = 13.841(3); b = 9.621(5); c = 7.482(2)Å; α = 98.05(4); β = 97.25(4); γ = 103.01(4)°; M = 536.59; V = 947.9ų; Z = 2; D_x = 1.879 g cm^?3; μ = 14.524 cm^?1, and space group $\text{P}\text{1}$. The crystal structure was solved using 1661 independent reflections measured on a single-crystal diffractometer (MoKα). The final R value is 0.056. The two crystallographic independent nickel atoms Ni(1) and Ni(2) are octahedrally coordinated: Ni(1) by four oxygen atoms and two water molecules, Ni(2) by six water molecules. Ni(1), closely connected to two P₄O₁₂ rings, forms a complex anion [Ni(P₄O₁₂)₂(H₂O)₂]^6? which is associated to ammonium polyhedra and [Ni(H₂O)₆]²⁺ octahedra. Another interesting feature of this atomic arrangement is the presence of a large channel (10 × 4) Ų parallel to the $\text{c}$ axis. The internal surface of this channel is covered by six zeolitic water molecules.     

Crystal structures of some niobium and tantalum oxides. VIII. The 5Rb2O:14.6Ta2O5 phase—A tunnel structure

Rb₁₀Ta_29.20O₇₈ crystallizes in the hexagonal system with unit-cell dimensions (from single-crystal data) a = 7.503(4)Å, c = 36.348(4)Å, and space group $\text{P6}{}_3\text{mmc}\text{, z = 1}$. The structure was solved using three-dimensional Patterson and Fourier techniques. Of the 666 unique reflections measured by counter techniques, 515 with I ? 3σ(I) were used in the least-squares refinement of the model to a conventional R of 0.057 (R_ω = 0.039). The structure of Rb₁₀Ta_29.20O₇₈ consists of layers of corner-sharing groups of six edge-shared octahedra separated by layers of single octahedra and double hexagonal tungsten bronze-like layers, these layers being perpendicular to the hexagonal c-axis. Nine-coordinate tricapped trigonal prismatic sites between the hexagonal tungsten bronze-like layers are partially occupied by Ta(V) ions.