Roberto Fernández de Luis

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.

Topological description of a 3D self-catenated nickel hybrid vanadate Ni(bpe)(VO3)2. Thermal stability, spectroscopic and magnetic properties

The three-dimensional Ni(bpe)(VO3)2 hybrid compound, where bpe is 1,2-di(4-pyridyl)ethene, (C12H10N2), has been synthesized using mild hydrothermal conditions under autogeneous pressure at 140 °C during five days, obtaining green emerald prismatic single-crystals suitable for X-ray structure determination. The compound crystallizes in the orthorhombic system, space groupPbcn, with a = 14.9066(5), b = 7.6269(2) and c = 26.9624(10) A, Z = 8, and R1 = 0.0373 for 4149 observed reflections. Single-crystal X-ray diffraction reveals that the crystal structure is composed of a 3D self-catenated 10-connected uninodal net constructed from 36-hxl like {NiV2O6} inorganic sheets linked through bpe ligands. The thermal evolution of the crystal parameters shows three different tendencies during the heating process: (i) initial contraction, (ii) thermal expansion, (iii) structural collapse due to the thermal instability of the organic ligand. The IR spectrum shows the vibrational modes of the bpe organic molecules and those of the (VO4)3− tetrahedral oxoanions. Diffuse reflectance electronic absorption spectroscopy shows the characteristic bands of the Ni(II) d8-high spin cation in slightly distorted octahedral geometry. From the positions of the bands in the electronic spectrum the Dq (940 cm−1) and Racah, B (930 cm−1) and C (3350 cm−1), parameters have been calculated. Magnetic measurements indicate the existence of antiferromagnetic interactions between the Ni(II) centres of the dinuclear units, with a value of the J/k = −59.4, with g = 2.076.

Four nodal self-catenated [{Ni8(Bpy)16}V24O68]·8.5(H2O), combining three dimensional metal–organic and inorganic frameworks

The chiral three dimensional crystal structure of [{Ni8(Bpy)16}V24O68]·8.5(H2O) is the first example of a hybrid vanadate combining a three dimensional metal–organic subnet with a three dimensional inorganic framework. The metal–organic framework consists of 3D + 2D polycatenation of a 3D “cds” like net and two 2D “sql” layers. The vanadium oxide subunit is a complex chain constructed from V5O15 cycles linked through a single tetrahedron. The vanadate chains are located in the channels of the metal–organic framework, and corner linked to the nickel metal centres giving rise to an unprecedented four nodal self-catenated framework. Moreover, as far as we as concerned, this is the first vanadate in which the V5O15 cycles has been isolated in the solid state. The crystallization water molecules are partially encapsulated between the organic ligands and the inorganic framework. The loss of crystallization water molecules gives rise to a contraction of the 0.6% of the unit cell volume. The IR spectrum shows the characteristic bands of the vanadium oxide subunit, and the bpy ligand. The BET measurement gives rise to a type III profile, (3.7 cm2 g−1), suggesting weak adsorbate-adsorbent interactions. The thermal evolution of the magnetic susceptibility is attributed to the zero-field splitting for eight non interacting Ni(II) cations.

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.

{Co(HBpe)2}(V4O12): pedal motion induced order–disorder P → C transition and disrupted C → C2/m displacive transition due to thermal instability

The one dimensional {Co(HBpe)2}(V4O12) inorganic–organic compound, where Bpe is 1,2-di(4-pyridyl)ethene (C12H10N2), has been synthesized using mild hydrothermal conditions under autogenous pressure at 120 °C for three days, obtaining single-crystals suitable for X-ray structure determination. The compound crystallizes in the triclinic system, space group P, with a = 15.4705(3) A, b = 11.8919(3) A, c = 7.8490(2) A, α = 88.252(2)°, β = 95.429(2)° and γ = 92.534(2)° at 100 K. The crystal structure possesses two crystallographically independent units, strong pseudo-symmetry elements, and a unit cell with a possible monoclinic metric at higher temperatures. At low temperature (100–293 K) the crystallographically independent units present perfectly ordered conformers of the HBpe ligand. The thermal evolution of the cell parameters was studied by single X-ray and powder X-ray diffraction, showing a clear anomaly in the 90–165 °C temperature range. The crystal structures determined at different temperatures (100, 293, 438, 503 and 533 K) show that a complete disorder of the HBpe ligand through pedal motion occurs between 90 °C and 165 °C. This dynamical process is completely reversible and gives rise to the P to C order–disorder structural transition. At higher temperatures the crystal structure tends to the monoclinic C2/m symmetric crystal structure, however, the thermal instability disrupts this hypothetical displacive structural transition. To the best of our knowledge this is the second polymeric compound in which the pedal motion has been reported. The spectroscopic and magnetic properties were also determined. The IR-spectrum shows the characteristic bands related to the organic ligand and V4O12 cycles. The thermal evolution of the magnetic susceptibility is related to magnetically isolated Co(II) centers exhibiting the spin–orbit coupling.

K2MnII2(H2O)2C2O4(HPO3)2: a new 2D manganese(II) oxalatophosphite with double-layered honeycomb sheets stabilized by potassium ions

A novel 2D metal oxalatophosphite, K2MnII2(H2O)2C2O4(HPO3)2 (KMnCP), was hydrothermally synthesized and characterized. The hexagonal morphology and crystal growth faces of KMnCP were predicted by the Bravais–Friedel–Donnay–Harker (BFDH) theory. Single crystal X-ray diffraction analysis revealed that the compound displays a unique double layered structure constructed from Mn(H2O)(HPO3) single layers linked by oxalate ligands, where the potassium levels interrupt the 3D connectivity through the organic bridges. Moreover, in order to classify this archetype, a crystallochemical revision of metal oxalatophosphites with anionic frameworks has been carried out. Several secondary building units (SBUs) formed from metal–phosphite substructures and different roles of the oxalate bridges have been observed, which has led us to propose a new structural classification for these kinds of materials that share common features with classic inorganic metal phosphates and coordination polymers. Finally, the thermal, spectroscopic and magnetic properties together with the electronic structure of the studied compound 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.

Water-induced phase transformation of a CuII coordination framework with pyridine-2,5-dicarboxylate and di-2-pyridyl ketone: synchrotron radiation analysis

Phase transformations in solid coordination frameworks (SCFs) are of interest for several applications, and this work reports a crystal-to-crystal transformation found for hydrogen-bonded CuII-based solid coordination frameworks (SCFs). Thus, the combination of PDC and (py)2C(OH)2 ligands, where PDC is pyridine-2,5-dicarboxylate and (py)2C(OH)2 is the derivative gem-diol of di-2-pyridyl ketone ((py)2CO), produces [Cu(PDC)((py)2C(OH)2)(H2O)] (1). Compound 1 transforms into [Cu(PDC)((py)2C(OH)2)] (2) by thermally-induced dehydration. Characterization of both compounds has been carried out by means of IR spectroscopy, single crystal and powdered sample X-ray diffraction (XRD) through conventional and synchrotron radiation, thermogravimetry (TG), X-ray thermodiffractometry (TDX), and scanning electron microscopy (SEM). Since the molecules of water in 1 are coordinated to the metal ions, their removal induces local distortions on the coordination sphere (square pyramidal for 1 and square planar for 2), which extend through the whole framework, affecting the hydrogen bond system and the packing. In fact, the wavy nature of the planes in 1 becomes sharper in 2, producing an oscillation of the framework, i.e., from open (1) to close (2) waves. The crystal-to-crystal transformation is reversible (1 ↔ 2) and hysteresis has been observed associated with it. Quantum-mechanical calculations based on density functional theory (DFT) show that the 1 ↔ 2 structural rearrangement involves a high amount of energy, which means that the role of the coordinated molecule of water exceeds the mere formation of hydrogen bonds.

Fluorinated mixed valence Fe(II)–Fe(III) phosphites with channels templated by linear tetramine chains. Structural and magnetic implications of partial replacement of Fe(II) by Co(II)

Three new fluorinated mixed valence Fe(II)–Fe(III) phosphites were synthesized by employing mild hydrothermal conditions. (H4baepn)0.5[FeIII2.3FeII1.7(H2O)2(HPO3)4−(x+y)(HPO4)x(PO4)yF4] (x ≃ 0.13, y ≃ 0.3) (1) (baepn = N,N′-bis(2-aminoethyl)-1,3-propanediamine (C7N4H20)) and the Co(II)-substituted phase with the formula (H4baepn)0.5[FeIII2.0FeII0.71CoII1.29(H2O)2(HPO3)4−x(HPO4)xF4] (x ≃ 0.38) (2) were studied by single crystal X-ray diffraction. The phase with the major content of Co(II), (H4baepn)0.5[FeIII2.0FeII0.62CoII1.38(H2O)2(HPO3)4−x(HPO4)xF4] (x ≃ 0.38) (3) was obtained as a polycrystalline powder and studied by Rietveld refinement by using the structural model of 2. These compounds were characterized by ICP-Q-MS, thermogravimetric and thermodiffractometric analyses, and XPS, IR, UV/vis and Mossbauer spectroscopy. The single crystal data indicate that phases 1 and 2 crystallize in the P21/c space group with lattice parameters a = 13.6808(4), b = 12.6340(2), c = 12.7830(3) A and β = 116.983(4)° for 1 and a = 13.6823(4), b = 12.6063(3), c = 12.7535(4) A and β = 116.988(4)° for 2, with Z = 4. The reciprocal space of 1 shows satellite reflections with a modulation wavevector q = 0.284(2)a* which indicate an incommensurate long-range order. The average structure of these compounds is built up by a 3D lattice constructed by inorganic layers of Fe(III) chains and Fe(II) and Co(II) dimers joined by phosphite groups partially substituted by HPO4 and PO4 tetrahedral groups. These anionic layers stack along the [100] direction encapsulating linear tetramines in eight-membered open channels involving host–guest interactions. Magnetic measurements of 1 and 3 showed antiferromagnetic coupling as the major interactions, exhibiting a weak ferromagnetic component together with a spin glass transition at low temperature in the case of 1. Heat capacity measurements showed a small anomaly at 20.5 K for 1 and a sharp magnetic peak at 28 K for 3. Unexpectedly, the small anomaly observed in 1 increased with the magnetic field and became better defined.

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.