A novel germanate, Cu2Fe2Ge4O13, with a four tetrahedra oligomer

The structure of Cu₂Fe₂Ge₄O₁₃, previously thought to be CuFeGe₂O₆, has been determined from single-crystal X-ray diffraction data to be monoclinic, P2₁/m, a=12.1050(6), b=8.5073(4), c=4.8736(2) Å, β=96.145(1)°, Z=2, with R1=0.0231 and wR2=0.0605. The unique structure has an oligomer of four germanate tetrahedra, cross-linked laterally by square-planar copper ions, joined end-to-end by a zigzag chain of edge-sharing iron oxide octahedra. Running along the a-direction the metal oxide chain consists of alternating Cu-Cu and Fe-Fe dimers. A hypothetical series of homologous structures (Cu_n−2Fe₂Ge_nO_3n+1 with n=3,4,…,∞) with different length germanate oligomers is proposed, where as n increases, the infinite chain of the CuGeO₃ is approached. In this context, Cu₂Fe₂Ge₄O₁₃ is viewed as being built from blocks of CuGeO₃ and the Fe oxide chains. This material has significance to the study of low-dimensional mixed-spin systems.     

Synthesis and crystal structures of CaY2Ge3O10 and CaY2Ge4O12

New compounds CaY₂Ge₃O₁₀ and CaY₂Ge₄O₁₂ were prepared by heating mixtures of CaCO₃, Y₂O₃ and GeO₂ at 1200 °C. CaY₂Ge₃O₁₀ is stable at 1300 °C, while CaY₂Ge₄O₁₂ decomposes into a melt and CaY₂Ge₃O₁₀ at approximately 1250 °C. We obtained single crystals of CaY₂Ge₃O₁₀ by cooling a sample with an initial composition of Ca:Y:Ge=1:2:8 from 1300 °C with a rate of −6 °C/h. The crystal structure of CaY₂Ge₃O₁₀ was determined by single crystal X-ray diffraction. CaY₂Ge₃O₁₀ crystallizes in the monoclinic space group P2₁/c with a=6.0906(8), b=6.8329(8), and β=109.140(3)°, Z=4, and R₁=0.029 for I>2σ(I). In the structure of CaY₂Ge₃O₁₀, Ca and Y atoms are situated disorderly in three 7-fold coordination sites between isolated germanate groups of triple GeO₄ tetrahedra, Ge₃O₁₀. The structural formula of CaY₂Ge₃O₁₀ is expressed as (Ca_0.45Y_0.55)(Ca_0.46Y_0.54)(Ca_0.09Y_0.91)Ge₃O₁₀. The crystal structure of CaY₂Ge₄O₁₂ was analyzed by the Rietveld method for the X-ray powder diffraction pattern. CaY₂Ge₄O₁₂ is isotypic with SrNa₂P₄O₁₂, crystallizing in the orthorhombic space group P4/nbm, a=9.99282(6), , Z=2, R_wp=0.092, R_p=0.067. CaY₂Ge₄O₁₂ contains four-membered GeO₄-tetrahedra rings, Ge₄O₁₂. Eight-fold coordinated square-anitiprism sites and 6-fold octahedral sites between the layers of the Ge₄O₁₂ rings are occupied by Y atom and Ca/Y atoms, respectively The structural formula is Y(Ca_0.5Y_0.5)₂Ge₄O₁₂.     

Multianvil high-pressure/high-temperature synthesis, crystal structure, and thermal behaviour of the rare-earth borogermanate Ce6(BO4)2Ge9O22

The new monoclinic cerium borogermanate Ce₆(BO₄)₂Ge₉O₂₂ was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 10.5 GPa and 1200 °C. Ce₆(BO₄)₂Ge₉O₂₂ crystallizes with two formula units in the space group P2₁/n with lattice parameters a=877.0(2), b=1079.4(2), c=1079.1(2) pm, and β=95.94(3)°. As the parameter pressure favours the formation of compounds with cations possessing high coordination numbers, it was possible to produce simultaneously BO₄-tetrahedra and GeO₆-octahedra in one and the same borogermanate for the first time. Furthermore, the cerium atoms show high coordination numbers (C.N.: 9 and 11), and one oxygen site bridges one boron and two germanium atoms (O^[3]), which is observed here for the first time. Besides a structural discussion, temperature-dependent X-ray powder diffraction data are presented, demonstrating the metastable character of this high-pressure phase.     

Crystal structure of hexagonal SrAl2O4 at 1073 K

The crystal structure of SrAl₂O₄ at 1073 K was determined from conventional X-ray powder diffraction data using direct methods, and it was further refined by the Rietveld method. The structure was hexagonal (space group P6₃, Z=6) with a=0.89260(3) nm, c=0.84985(2) nm and V=0.58639(3) nm³. Final reliability indices were R_wp=7.87%, R_p=5.87% and R_B=4.19%. The [AlO₄] tetrahedra are linked to form trigonally distorted rings and they are joined in layers. These layers are stacked with a two-layer repeat and connected by the tetrahedral apices. All of the Sr atoms occupy the centers of the rings when viewed along the c-axis. The structure is described as a stuffed derivative of tridymite.     

Enthalpy of mixing in 0.8[xB2O3-(1 − x)P2O5]-0.2Na2O glasses at 298 K

0.8[xB₂O₃-(1 − x)P₂O₅]-0.2Na₂O (with 0 ≤ x ≤ 1) glasses have been characterized by solution calorimetry at 298 K in acid solvent. The experimental data showed a strong negative departure of the enthalpy of mixing from the ideality described by the equation (in kJ/mol): ΔH = x(1 − x)(−660.2 + 570x). The results were interpreted on the basis of the structural data. Enthalpies of mixing were consistent with sub-regular solution behaviour.     

Cluster self-organization of Na-TR-Ge-O-H (TR = La-Lu, Y, and Sc) germanate systems: Suprapolyhedral precursor clusters and self-assembly of Na2Pr6Ge8O26, Na4Sc2Ge4O13, and Na5ScGe4O12 crystal structures

In an M-T-O model system (M is a polyvalent metal; T = Ge or Si), we consider initial stages of formation of cyclic MT clusters and the mechanism of their modification by T tetrahedra. The polyhedron ratio T/M in clusters increases progressively during modeling from one in M₂T₂ to two (M₂T₂ + 2T = M₂T₄), three (M₂T₂ + 2T₂ = M₂T₆), and four (M₂T₂ + 2T + 2T₂ = M₂T₈). These types of clusters were used to find precursor clusters for T-condensed structures of Na₂Pr₆Ge₈O₂₆, Na₄Sc₂Ge₄O₁₃, and Na₅ScGe₄O₁₂. The TOPOS program package was used to carry out the complete 3D reconstruction of the self-assembly of Na,TR germanates: precursor cluster → primary chain → microlayer → microframework (supraprecursor) → ... framework. In all structures, as previously in six orthotetrahedral Na,TR germanate structures, the basic invariant type of four-polyhedral cyclic precursor cluster M₂T₂ was identified; this cluster is built of TR polyhedra, with CN = 6 or 7, linked via orthotetrahedra. The features of the generation of a Ge radical were considered in the form of a Ge₂O₇ chain and a Ge₄O₁₂ ring in various layers of the Na₂Pr₆Ge₈O₂₆ composite structure, a Ge₄O₁₃ chain in Na₄Sc₂Ge₄O₁₃, and a Ge₁₂O₃₆ ring in the Na₅ScGe₄O₁₂ superionic conductor. Original Russian Text ? G.D. Ilyushin, L.N. Dem’yanets, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 484–496.     

Enthalpy of mixing in 0.8[xB2O3-(1 − x)SiO2]-0.2K2O melts at 973 K

0.8[xB₂O₃-(1 − x)SiO₂]-0.2K₂O (with 0 ≤ x ≤ 1) glasses were synthesized by melt quenching techniques. DSC curves of the glasses exhibit only one glass transition. Calorimetric measurements of heats of dissolution in lead borate at 973 K indicated small negative enthalpies of mixing. Consequently phase separation was not observed over the whole composition range. The results are in good agreement with the structural data available in the literature.     

Metamagnetic transition in the 75 K antiferromagnet Gd4Co2Mg3

Gd₄Co₂Mg₃ (Nd₄Co₂Mg₃ type; space group P2/m; a=754.0(4), b=374.1(1), c=822.5(3) pm and β=109.65(4)° as unit cell parameters) was synthesized from the elements by induction melting in a sealed tantalum tube. Its investigation by electrical resistivity, magnetization and specific heat measurements reveals an antiferromagnetic ordering at T_N=75(1) K. Moreover, this ternary compound presents a metamagnetic transition at low critical magnetic field (H_cr=0.93(2) T at 6 K) and exhibits a magnetic moment of 6.3(1) μ_B per Gd-atom at 6 K and H=4.6 T. Due to this transition the compound shows a moderate magnetocaloric effect; at 77 K the maximum of the magnetic entropy change is ΔS_M=−10.3(2) J/kg K for a field change of 0-4.6 T. This effect is compared to that reported previously for compounds exhibiting a magnetic transition in the same temperature range.     

A pyrazole-based orthogonal ferromagnetically coupled [2 × 2] homoleptic square Cu4 grid: Magnetostructural correlations

The synthesis and structure of a pyrazole-based orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid complex [Cu₄(PzOAPyz)₄(ClO₄)₂](ClO₄)₂ · 6H₂O (1), formed by the reaction between the ditopic ligand PzOAPyz and Cu(ClO₄)₂ · 6H₂O, are described. The ligand contains terminal pyrazole and pyrazine residues bound to a central flexible diazine subunit (N–N) as well as one potentially bridging alkoxo group. The two adjacent metal centers are linked by an alkoxo oxygen forming essentially a square Cu₄(μ-O₄) cluster. In the Cu₄(μ-O₄) core, out of the four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by one of the oxygen atoms of a coordinated perchlorate ion. Complex 1 has been characterized structurally and magnetically. Although the large Cu–O–Cu bridge angles (137–138°) and short Cu–Cu distances (3.964–3.970 Å) are suitable for the transmission of the expected antiferromagnetic coupling, the square-based Cu₄(μ-O₄) cluster exhibits an intramolecular ferromagnetic exchange (J = 7.47 cm⁻¹) between the metal centers with an S = 2 magnetic ground state associated with the quasi orthogonal arrangement of the magnetic orbitals (d_x2-y2${\text{d}}_{x^2-y^2}$). The exchange pathway parameters have been evaluated from density functional calculations.     

Synthesis, crystal structure and thermal behavior of a novel oxoborate SrBi2B4O10

A new compound, SrBi₂B₄O₁₀, has been grown by cooling a melt with the stoichiometric composition. It is triclinic, P−1, a=6.819(1), b=6.856(1), c=9.812(2) Å, α=96.09(1), β=109.11(1), γ=101.94(1)°, V=416.5(1) Å³, Z=2. The crystal structure of the compound has been solved by direct methods and refined to R₁=0.050 (wR₂=0.128). The structure contains Bi-O pseudolayers build up from Bi-O chains involving oxocentred OBi₃ triangles. Sr atoms and [B₄O₉]⁶⁻ isolated anions (4B:3Δ□:<2Δ□>Δ) are located between the Bi-O packages.The thermal treatment as well as DSC experiment showed that the compound melts above 800 °C presumably according to the peritectic reaction: SrBi₂B₄O₁₀ ↔ SrB₂O₄+SrB₄O₇+ Liquid. According to high-temperature X-ray powder diffraction study thermal expansion of SrBi₂B₄O₁₀ structure is anisotropic (α₁₁=13, α₂₂=9, α₃₃=2, α_V=24×10⁻⁶ °C⁻¹).     

Preparation, crystal structure, and magnetic studies of Na3Fe2Mo5O16, a new oxide containing Mo3O13 clusters

The complex oxide Na₃Fe₂Mo₅O₁₆ has been synthesized, and its crystal structure was determined by single-crystal X-ray diffraction (space group (SG) P-3m1; a=5.7366(6) Å, c=22.038(3) Å; Z=2). The compound can be considered as a new structure type containing Mo₃O₁₃ cluster units, which can be derived from the Na₂In₂Mo₅O₁₆ structure model by doubling of the cell along the c-axis. Na₃Fe₂Mo₅O₁₆ crystallizes in centrosymmetric SG (P-3m1) and the positions of the sodium atoms are fully occupied in contrast to the proposed Na₂In₂Mo₅O₁₆ model SG (P3m1). Magnetic properties of Na₃Fe₂Mo₅O₁₆ were studied by superconducting quantum interference device measurements, revealing antiferromagnetic ordering below Tχ_max=10(1) K. Thermal stability in air was investigated by in situ high-temperature X-ray powder diffraction. Structural relationships to Na₂In₂Mo₅O₁₆ and NaFe(MoO₄)₂ are discussed.     

Ab initio structure determination of new compound Li4CaB2O6

A new compound, Li₄CaB₂O₆, has been synthesized by solid-state reaction and its structure has been determined from powder X-ray diffraction data by direct methods. The refinement was carried out using the Rietveld methods and the final refinement converged with R_p=10.4%, R_wp=14.2%, R_exp=4.97%. This compound belongs to the orthorhombic space group Pnnm, with lattice parameters a=9.24036(9) Å, b=8.09482(7) Å, and c=3.48162(4) Å. Fundamental building units are isolated [BO₃]³⁻ anionic groups, which are all parallel to the a-b plane stacked along the c-axis. The Ca atoms are six-coordinated by the O atoms to form octahedral coordination polyhedra, which are joined together through edges along the c-axis, forming infinitely long three-dimensional chains. The Li atoms have a four-fold and a five-fold coordination with O atoms that lead to complex Li-O-Li chains that also extend along the c-axis. The infrared spectrum of Li₄CaB₂O₆ was also studied, which is consistent with the crystallographic study.     

Cu2(bipy)2V6O17: A new type of layered inorganic–organic hybrid copper(II) vanadate

Hydrothermal reaction of copper(II) acetate, 2,2′-bipyridine (bipy) and NH₄VO₃ at 170 °C lead to a new layered polyoxovanadate with organically covalent-bonded copper(II) complex, Cu₂(bipy)₂V₆O₁₇ (1). Cu₂(bipy)₂V₆O₁₇ (1) is a new copper(II) vanadium(V) oxide featuring a new layered architecture, in which the V₂O₇ dimeric units and the cyclic tetranuclear V₄O₁₂ cluster units are interconnected via corner sharing into a unique one-dimensional {V₆O₁₇}⁴⁻ anionic chain, such chains are further bridged by {Cu(bipy)}²⁺ complex cations into a 010 organic–inorganic hybrid layer.     

Thermodynamic evaluation and optimization of the (Na2SO4 + K2SO4 + Na2S2O7 + K2S2O7) system

A complete, critical evaluation of all phase diagram and thermodynamic data was performed for all phases of the (Na₂SO₄ + K₂SO₄ + Na₂S₂O₇ + K₂S₂O₇) system and optimized model parameters were obtained. The Modified Quasichemical Model in the Quadruplet Approximation was used for modelling the liquid phase. The model evaluates first- and second-nearest-neighbour short-range ordering, where the cations (Na⁺ and K⁺) are assumed to mix on a cationic sublattice, while anions were assumed to mix on an anionic sublattice. The Compound Energy Formalism was used for modelling the solid solutions of (Na,K)₂SO₄ and (Na,K)₂S₂O₇. The models can be used to predict the thermodynamic properties and phase equilibria in multicomponent heterogeneous systems. The experimental data from the literature were reproduced within experimental error limits.     

Temperature dependence of structural parameters in oxide-ion-conducting Nd9.33(SiO4)6O2: single crystal X-ray studies from 295 to 900 K

Crystallographic space group, structural parameters and their thermal changes in oxide-ion-conducting Nd_9.33(SiO₄)₆O₂ were investigated using high-temperature single-crystal X-ray diffraction experiments in the temperature range of 295?T?900 K. The title compound has the apatite structure (space group P6₃/m), and no notable structural change occurred over the temperature range examined. Observed anisotropy in thermal motions of oxide ions which belong to SiO₄ tetrahedron indicated high rigidity of the tetrahedron in the structure, indicating that they form sp3 hybrid orbitals and the ligand oxygens do not take part in oxide-ion conductivity. Virtually full occupation of the 6h Nd site and highly anisotropic displacements of oxide ion inside the hexagonal channel were maintained over the temperature range examined. This result confirms that oxide-ion transport inside the hexagonal channel is the dominant process of conduction in the title compound.     

Preparation and crystal structure of [Bi3I(C4H8O3H2)2(C4H8O3H)5]2Bi8I30 containing the novel polynuclear [Bi8I30] anion

Preparation and crystal structure of the novel compound [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ are reported. The title compound is prepared by heating of BiI₃ and diethylene glycol at 413 K in a sealed quartz glass tube filled with argon. Deep red single crystals are grown and applied to perform X-ray powder diffraction and X-ray single-crystal diffraction measurements. The compound crystallizes triclinic with space group P-1: Z=2, a=13.217(1) Å, b=15.277(1) Å, c=22.498(1) Å, α=84.33(1), β=73.18(1), γ=67.48(1). [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]₂Bi₈I₃₀ comprises the novel polynuclear [Bi₈I₃₀]⁶⁻ anion and [Bi₃I(C₄H₈O₃H₂)₂(C₄H₈O₃H)₅]³⁺ as the cation. Cation as well as the anion can be assumed to represent intermediates between solid BiI₃ and BiI₃ completely dissolved in diethylene glycol.     

A novel cesium hydroxygallophosphate with a layered structure built up of rutile ribbons: CsGa2(OH)2[(PO4)H(PO4)]

A new cesium gallophosphate, CsGa₂(OH)₂[(PO₄)H(PO₄)], with an original layer structure has been synthesized by hydrothermal route and characterized by single-crystal X-ray diffraction (R=0.0344, R_w=0.0319). Its structure crystallizes in the monoclinic space group P2₁/a with cell parameters , , , β=93.36(4)° and Z=2. It consists of [Ga(OH)PO₄]_∞ layers built up of rutile ribbons interconnected through PO₄ tetrahedra. The structure of CsGa₂(OH)₂[(PO₄)H(PO₄)] is closely related to those of (NH₄)Ga(OH)PO₄ and (en)Ga₂(OH)₂(PO₄)₂ (en=ethylenediamine [H₃N(CH₂)₂NH₃]²⁺). The three structures differ mainly from each other by the relative positions and the spacing of the successive layers, which are governed by different hydrogen bonding modes between [Ga(OH)PO₄]_∞ layers and the interleaved species. The title compound presents strong symmetric hydrogen bonds O---H---O which bridge two PO₄ tetrahedra of two successive layers. As a consequence, the distance between the layers is significantly shorter than in the two other amine compounds.     

Hydrothermal syntheses and structures of two novel vanadium selenites, {[VO(OH)(H2O)](SeO3)}4·2H2O and (H3NCH2CH2NH3)[(VO)(SeO3)2]

Two novel vanadium selenites {[VO(OH)(H₂O)](SeO₃)}₄·2H₂O 1 and (H₃NCH₂CH₂NH₃)[(VO)(SeO₃)₂] 2 were synthesized by hydrothermal method and their crystal structures were determined by single-crystal X-ray diffraction. It is characterized by inductively coupled plasma (ICP), thermogravimetric (TG) and elemental analyses. Compound 1 crystallizes in the monoclinic system, space group C2/c, a=21.2250(11) Å, b=12.6309(6) Å, c=17.0249(10) Å, β=96.830(3)°, V=4531.8(4) Å³ and Z=8, R₁ [I>2σ(I)]=0.0344, wR₂ [I>2σ(I)]=0.119; Compound 2 crystallizes in the monoclinic system, space group P2₁/c, a=9.6389(4) Å, b=6.9922(3) Å, c=15.0324(5) Å, β=102.297(2)°, V=989.90(7) Å³ and Z=4, R₁ [I>2σ(I)]=0.0452, wR₂ [I>2σ(I)]=0.117. {[VO(OH)(H₂O)](SeO₃)}₄·2H₂O has a 1D structure constructed from the {[VO(OH)(H₂O)](SeO₃)}_∞ chains. (H₃NCH₂CH₂NH₃)[(VO)(SeO₃)₂] has a layered structure composed of alternating VO₅ and SeO₃ units with protonated ethylenediamine as interlayer guest.     

Crystal structure and magnetic properties of the 1D bimetallic thiocyanate bridged compound: {(CuL1)[Co(NCS)4]}(L1 = N-rac-5,12-Me2-[14]-4,11-dieneN4)

The synthesis, crystal structure and magnetic properties are reported for the new bimetallic compound {(CuL₁)[Co(NCS)₄]} where L₁ = N-rac-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene. The complex forms a one-dimensional zig-zag coordination polymer along the crystallographic c axis, with Co(II) and Cu(II) ions connected via thiocyanate bridges. The Co(II) centre in the [Co(NCS)₄] fragment approximates a distorted tetrahedral symmetry. The Cu(II) geometry is a distorted tetragonal bipyramid with the apical position occupied by the bridging thiocyanate ligand and the basal ones by the four nitrogen atoms from the macrocyclic ring. The polymer chain nearest Cu(1)?Co(1) distances are 6.4152(9) and 6.0988(9) Å and the nearest Cu(1)?Co(1) interchain distances are 6.8609(9), 6.9628(9) and 6.0336(10) Å. The magnetization measurements for the examined compound have been carried out over the range 1.8–300 K. This data suggest ferromagnetic interactions through the thiocyanate bridge.