Edurne S. Larrea

Thermal response, catalytic activity, and color change of the first hybrid vanadate containing Bpe guest molecules.

Four isomorphic compounds with formula [{Co2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoBpe 1; [{CoNi(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, CoNiBpe 2; [{Co0.6Ni1.4(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiCoBpe 3; and [{Ni2(H2O)2(Bpe)2}(V4O12)]·4H2O·Bpe, NiBpe 4, have been obtained by hydrothermal synthesis. The crystal structures of CoBpe 1 and NiBpe 4 were determined by single-crystal X-ray diffraction (XRD). The Rietveld refinement of CoNiBpe 2 and NiCoBpe 3 XRD patterns confirms that those are isomorphic. The compounds crystallize in the P1̅ space group, exhibiting a crystal structure constructed from inorganic layers pillared by Bpe ligands. The crystal structure contains intralayer and interlayer channels, in which the crystallization water molecules and Bpe guest molecules, respectively, are located. The solvent molecules establish a hydrogen bonding network with the coordinated water molecules. Thermodiffractometric and thermogravimetric studies showed that the loss of crystallization and coordinated water molecules takes place at different temperatures, giving rise to crystal structure transformations that involve important reduction of the interlayer distance, and strong reduction of crystallinity. The IR, Raman, and UV-vis spectra of the as-synthesized and heated compounds confirm that the structural building blocks and octahedral coordination environment of the metal centers are maintained after the structural transformations. The color change and reversibility of the water molecules uptake/removal were tested showing that the initial color is not completely recovered when the compounds are heated at temperatures higher than 200 °C. The thermal evolution of the magnetic susceptibility indicates one-dimensional antiferromagnetic coupling of the metal centers at high temperatures. For NiCoBpe 3 and NiBpe 4 compounds magnetic ordering is established at low temperatures, as can be judged by the maxima observed in the magnetic susceptibilities. CoNiBpe 2 was proved as catalyst being active for cyanosilylation reactions of aldehydes.

M(C6H16N3)2(VO3)4 as heterogeneous catalysts. Study of three new hybrid vanadates of cobalt(II), nickel(II) and copper(II) with 1-(2-aminoethyl)piperazonium

Three new hybrid vanadates have been synthesized under hydrothermal conditions with the formula M(C(6)H(16)N(3))(2)(VO(3))(4), where M = Co(II), Ni(II) and Cu(II). The structural analyses show that the phases are isostructural and crystallize in the monoclinic space group P2(1)/c. These compounds show a two-dimensional crystal structure, with sheets composed of [VO(3)](n)(n-) chains and metal centres octahedrally coordinated, chelated by two 1-(2-aminoethyl)piperazonium ligands. The thermal study reveals that the copper containing phase is less stable than the cobalt and nickel containing ones. The IR spectra of the three phases are very similar, with little differences in the inorganic bond region of the copper containing phase. The UV-visible spectra show that the cobalt(II) and the nickel(II) are in slightly distorted octahedral environments. The catalytic tests show that the phases act as heterogeneous catalysts for the selective oxidation of alkyl aryl sulfides, with both H(2)O(2) and tert-butylhydroperoxide as oxidizing agents. The influence of the steric hindrance in the kinetic profile has been studied. The catalytic reactions induce the partial amorphization of the phases.

Hybrid vanadates constructed from extended metal–organic arrays: crystal architectures and properties

The hybrid vanadates exhibit structural archetypes between the hybrid zeotypes, in which the inorganic framework is surrounding an organic cation acting as a template, and metal–organic frameworks whose crystal structures are constructed from metal nodes or clusters linked by organic bridges. Here we present the summary of the studies carried out on hybrid vanadates constructed from extended metal–organic arrays. The crystal structures are systematically described and classified according to the dimensionality of the inorganic and metal–organic frameworks. Finally, the magnetic, thermal and catalytic properties of different structural archetypes are discussed.

Composite β-AgVO3@V1.65+V0.44+O4.8 hydrogels and xerogels for iodide capture

Herein, we report on the study of silver vanadium oxide (β-AgVO3) and slightly reduced vanadium oxide (V1.65+V0.44+O4.8) composite hydrogels, which were synthesized under ambient conditions using a mixture of two solutions. Acidification of the reaction media plays a crucial role in the chemical and physical properties of the hydrogels. The non-covalent cross linked three dimensional network of silver vanadium oxide and vanadium oxide nano-ribbons traps water thus stabilizing the gel form of the materials. Xerogels of the selected materials were produced by drying the hydrogels at 70 °C. The morphology and composition of the nano-ribbons were studied using scanning (SEM) and transmission (TEM) electron microscopy and EDX and EELS compositional analyses of selected areas and punctual microanalyses. In addition, the three dimensional reconstruction of a single nano-ribbon was carried out using electron tomography. Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS) and double titration chemical analyses together with inductively coupled plasma mass spectroscopy (ICP-AES) chemical analyses allowed the proposal of average chemical formulas and vanadium oxidation state. EPR spectroscopy and magnetic susceptibility measurements confirm the existence of a secondary slightly reduced vanadium oxide within the silver vanadium oxide gels jellified under acidic conditions. The micro and mesoporosity of the xerogels were studied using N2 adsorption isotherms, which reveal different porous structures depending on the synthetic conditions. Finally, due to their porous and reactive nature, the hydrogels, organogels and xerogels were tested against methylene blue, crystal violet and iodide adsorption.

Crystal structure of (NH4)2[FeII5(HPO3)6], a new open-framework phosphite

(NH4)2[FeII 2(HPO3)6] exhibits an open-framework structure with channels in which disordered ammonium cations are situated.

Compositional space diagrams and crystallization sequences in M/Bpa/NaVO3 (M = Ni, Co) systems. Physical properties of [{Ni(H2O)(Bpa)}(VO3)2]·2H2O and {Co(Bpa)}(VO3)2 3D hybrid vanadates

The 3D hybrid compounds {Co(Bpa)}(VO3)2 (1) and [{Ni(H2O)(Bpa)}(VO3)2]·2H2O (2), where Bpa is 1,2-di(4-pyridil)ethane, have been synthesized using mild hydrothermal conditions. The compositional diagrams for the Co(II)/Bpa/VxOy and Ni(II)/Bpa/VxOy systems have been constructed and qualitative crystallization sequences have been proposed. The 3D crystal structures of both compounds are closely related, and are constructed of inorganic layers pillared by the organic ligand. The UV-vis spectra for (1) shows the characteristic bands of the Co(II) d7high-spin cation in a slightly distorted trigonal bipyramid geometry. The thermal behaviour of (1) allows the determination of the expansion coefficients for the cell and angle parameters, which were closely related to the different types of bonds that exist in the crystal structure. The cobalt compound exhibits antiferromagnetic coupling of the cobalt centres within the inorganic layers, probably coupled in dimeric units, as is expected for the different magnetic exchange pathways. For (2), the diffuse scattering is probably related to the motion of the crystallization water molecules, which is observed in the (h0l), (h2l), (hk0) and (hk2) planes.

Crystal structure of K0.75[FeII3.75FeIII1.25(HPO3)6]·0.5H2O, an open-framework iron phosphite with mixed-valent FeII/FeIII ions

K0.7[FeII 3.7FeIII 1.3(HPO3)6]·5H2O was synthesized under mild hydrothermal conditions. The open-framework phosphite contains channels extending along [001] in which disordered potassium cations and water molecules are located.

Catalytic behaviour of two structurally related vanadyl arsenates

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