Polyoxovanadate Research Articles

A Versatile Polyoxovanadate in Diverse Cation Matrices: A Supramolecular Perspective.

A series of decavanadate based compounds, formulated as [Co(H2O)6][{Na4(H2O)14}{V10O28}]·4H2O (1), [Zn(H2O)6][Na3(H2O)14] [HV10O28]·4H2O (2), [HMTAH]2 [{Zn(H2O)4}2{V10O28}]·2H2O (3), [{Co(3-amp)(H2O)5}]2 [3-ampH]2 [V10O28] · 6H2O (4), [4-ampH]10[{Na(H2O)6}{HV10O28}][V10O28]·15H2O (5), [{4-ampH}6 {Co(H2O)6}3][V10O28]2·14H2O (6), and [{4-ampH}10{Zn(H2O)6}][V10O28]2·10H2O (7), have been synthesized (where HMTAH = mono-protonated hexamethylenetetramine, 3-ampH = protonated 3-amino pyridine and 4-ampH= protonated 4-aminopyridine) from the relevant aqueous sodium-vanadate solution, by varying the pH of the solution and amino pyridine/hexamine derivatives as well as transition metal salts (Co(II)- and Zn(II)-salts). In this series of compounds 1–7, the polyoxovanadate (POV) cluster [V10O28]6− is the common cluster anion, stabilized by diverse cations. The diverse supramolecular patterns around the decavanadate cluster anion in different cationic matrices have been described to understand the microenvironment in the decavanadate-based minerals. All of these compounds have solvent water molecules in their respective crystal lattices. Since water can interact directly with cations and anions, providing an additional stability and structural diversity, we have analyzed supramolecular water structures in all these compounds to comprehend the role of the lattice water in the formation of natural decavanadate containing minerals. Compounds 1–7, that are isolated at an ambient condition from aqueous solution, are characterized by routine spectral analysis, elemental analyses and finally unambiguously by single crystal X-ray crystallography.

Diversified polyoxovanadate derivatives obtained by copper(i)-catalysed azide-alkyne cycloaddition reaction: their synthesis and structural characterization.

In this work, we confirmed that the copper-catalysed azide-alkyne cycloaddition (CuAAC) reaction is an effective method for the organic-functionalization of polyoxometalates (POMs). Herein, for the first time, four novel 1,2,3-triazole functionalized polyoxovanadate (POV) organic-inorganic hybrids, (Bu4N)2[V6O13{(OCH2)3C5H6N3O}2]·1.5CH3CN 2, (Bu4N)2[V6O13{(OCH2)3C7H8N3O2}2]·2CH3CN 3, (Bu4N)2[V6O13{(OCH2)3C11H10N3}2] 4 and (Bu4N)2[V6O13{(OCH2)3C10H7N3Cl}2] 5 were prepared through the CuAAC reaction using the azide functionalized hexavanadate, (Bu4N)2[V6O13{(OCH2)3CCH2N3}2]·2.5CH3CN 1, as the precursor, where CuI was used as the catalyst and N,N-diisopropylethylamine (DIPEA) as a stabilizer for CuI. All the four compounds were structurally and compositionally characterized by single-crystal X-ray diffraction, elemental analyses, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), 1H NMR, ESI-MS, UV-Vis and thermogravimetric analysis (TGA).

Alcohol Oxidations Using Reduced Polyoxovanadates

A full account of our recently communicated room temperature alcohol oxidation using reduced polyoxovanadates (r‐POVs) is presented. Extensive optimizations revealed optimal conditions employing 0.02 equiv. of r‐POV catalyst Cs5(V14As8O42Cl), 5 equiv. tert‐butyl hydrogen peroxide (tBuOOH) as the terminal co‐oxidant, in an acetone solvent for the quantitative oxidation of aryl‐substituted secondary alcohols to their ketone products. The substrate scope tolerates most aryl substituted secondary alcohols in good to quantitative yields while alkyl secondary and primary activated alcohols were sluggish in comparison under similar conditions. Catalyst recyclability was successful on a 1.0 mmol scale of starting alcohol 1‐phenylethanol. The oxidation was also successfully promoted by the VIV/VV mixed valent polyoxovanadate (POV) Cs11Na3Cl5(V15O36Cl). Finally, a third POV, Cs2.64(V5O9)(AsO4)2, was investigated for catalytic activity using our established reaction protocol, but proved ineffective as compared to the other two r‐POV catalysts. This study expands the field of POM‐mediated alcohol oxidations to include underexplored r‐POV catalysts. While our catalysts do not supplant the best catalysts known for the transformation, their study may inform the development of other novel oxidative transformations mediated by r‐POVs.

The Cu(i)-catalysed Huisgen 1,3-dipolar cycloaddition route to (bio-)organic functionalisation of polyoxovanadates.

The [V6O13{(OCH2)3CCH2OCH2C[triple bond, length as m-dash]CH}2]2- with two terminal alkyne functionalities exhibits excellent reactivity towards (bio-)organic azides. The designed synthetic protocol for the generation of triazol-modified Lindqvist hexavanadates grants access to bio-"clicked" polyoxometalates with spectroscopically detectable 51V nuclei.

Self-Assembly of Polyoxovanadate-Containing Fluorosurfactants.

Two novel polyoxovanadate (POV)-containing fluorosurfactants, each with two hydrophobic fluorinated "tails" and one nanosized, hydrophilic, rigid POV "head group", are synthesized for the first time. They self-assemble into spherical, bilayer vesicles in acetonitrile/water mixed solvents, as evidenced by systemic studies using laser light scattering (LLS) and electron microscopy techniques. The vesicle sizes demonstrate dynamic change over different solvent compositions mainly as a result of the solvent swelling of the fluorocarbon chains, although the charge number on the POVs changes over the solvent polarity as well.

A Vanadium (VO2+) Metal–Organic Framework: Selective Vapor Adsorption, Magnetic Properties, and Use as a Precursor for a Polyoxovanadate

The reaction of VOSO(4) with 2-carboxyethylphosphonic acid (H(2)-CEP) in presence of piperazine (PIP) produces a 3D inorganic-organic hybrid framework, {(H(2)PIP)(0.5)[VO(CEP)]·H(2)O} (1) with bidirectional channels occupied by the H(2)PIP cations and H(2)O molecules. The PO(3)(2-) unit of CEP connects three V(IV) centers to generate a 1D ladder, which is further linked to four such ladders by the CEP linkers to form a 3D hybrid framework. The dehydrated framework, {(H(2)PIP)(0.5)[VO(CEP)]} (1') shows selective and gated adsorption behavior with H(2)O but not with methanol and ethanol. Very interestingly, when 1 is treated with an aqueous solution of LiNO(3)/NaNO(3), the framework breaks down and results in a new polyoxovanadate (POV) cluster, [H(5)(H(2)PIP)(3)][V(V)(12)V(IV)(2)O(38)(PO(4))]·8H(2)O (2) at pH ≈ 2.1. The cluster has been characterized by single-crystal X-ray diffraction, (31)P NMR, EPR, and magnetic studies. The temperature-dependent magnetic susceptibility measurement suggests antiferromagnetic ordering in 1 with T(N) ≈ 3.8 K.

Polyoxometalates: Toward new materials

This article describes an account of some of our polyoxometalate (POM)-based research, we have been doing in our laboratory last several years. There are several well-defined POM cluster anions, that are structurally characterized. We have chosen Anderson-type of heteropolyanion [Al(OH)6Mo6O18]3 − and explored its linking propensity in different dimensions using ‘s’, ‘d’ and ‘f’ block elements as linkers. We have demonstrated how a lanthanide linker provides a new pathway in forming a two-dimensional linked {As8V14} system [{Ln(H2O)6}2As8V14O42(SO3)]n · 8nH2O, that is derived from discrete {As8V14} cluster containing compound (NH4)6[As8V14O42(SO3)]. A polyoxometalate compound has been described in which a reduced tungstovanadate–heteropolyanion clusters get linked via capped V = O groups into one-dimensional chains. All these systems have already been reported elsewhere. The last portion of this article will be described by a new system [3-ampH]6[V10O28] · 2H2O having discrete molecular structure and extended supramolecular structure. The synthesis and solid state structure of a new polyoxovanadate(POV)-based compound [3-ampH]6[V10O28]⋅2H2O have been described emphasizing the supramolecular interactions between the isopolyanion [V10O28]6- and surrounding organic cations [3-ampH]1+. Also includes a brief review of seven polyoxometalate(POM)-based compounds that are already reported from our laboratory.

Salt-Templated Mesoporous Solids Comprised of Interlinked Polyoxovanadate Clusters

The utility of molten salts has been demonstrated in the synthesis of the first family of mesoporous salt-inclusion solids featuring [V(4)O(16)] and [V(5)O(17)] polyoxovanadate (POV) units interlinked by As(5+) cations. Despite a high-temperature synthesis, these new solids exhibit unusually porous ( approximately 2-nm-diameter) vanadium arsenate frameworks. Disordered metal chloride salts reside inside the pores, leading to relatively large voids (up to approximately 7.2% of the unit cell volume), which were confirmed by surface area (SA) measurements of the as-prepared polycrystalline samples ( approximately 90-110 m(2)/g). Given the potential utility of porous POV-containing materials, efforts were made to study changes in the SAs (showing approximately 35-70% increases) upon salt removal and redox chemistry.

A Novel Expansion Mode of Polyoxovanadate Clusters: Synthesis, Crystal Structure and Properties of {[Cu(H2O)(C5H14N2)2]2[V16O38(Cl)]}·4(C5H16N2)

AbstractThe new polyoxovanadate (POV) compound {[Cu(H2O)(C5H14N2)2]2[V16O38(Cl)]}·4(C5H16N2) was synthesized under solvothermal conditions and crystallizes in the tetragonal space group I41/amd with a = 13.8679(6), c = 45.558(2) Å, V = 8761.7(7) Å3. The central structural motif is a {V16O38(Cl)} cluster constructed by condensation of 16 square‐pyramidal VO5 polyhedra. The cluster hosts a central Cl– anion. According to valence bond sum calculations, chemical analysis and magnetic properties the cluster anion may be formulated as [V15IVVVO38(Cl)]12–, i.e., only one vanadium atom is not reduced. To the best of our knowledge this is the first reported {V16O38(X)} cluster in this VIV:VV ratio. The presence of the two different vanadium oxidation states is clearly seen in the IR spectrum. An unusual and hitherto never observed structural feature is the binding mode between the [Cu(H2O)(C5H14N2)2]2+ complexes and the [V15IVVVO38(Cl)]12– anion. The Cu2+ ion binds to a μ2‐O atom of the cluster anion whereas in all other transition metal complex‐augmented POVs bonding between the transition metal cation and the anion occurs through terminal oxygen atoms of the POV. The magnetic properties are dominated by strong antiferromagnetic exchange interactions between the V4+ d1 centers, whereas the Cu2+ d9 cations are magnetically decoupled from the cluster anion. Upon heating, the title compound decomposes in a complex fashion.

Discrete Polyoxovanadate Cluster into an Organic Free Metal-Oxide-Based Material: Syntheses, Crystal Structures, and Magnetic Properties of a New Series of Lanthanide Linked-POV Compounds [{Ln(H2O)6}2As8V14O42(SO3)]·8H2O (Ln = La3+, Sm3+, and Ce3+)

This article describes the linking propensity of the sulfite encapsulated polyoxovanadate (POV) anion, [As(8)V(14)O(42)(SO(3))](6-), with aqua-lanthanide complex cations [Ln(H(2)O)(6)](3+) in a controlled wet synthesis resulting in a series of organic free metal-oxide-based materials [{Ln(H(2)O)(6)}(2)As(8)V(14)O(42)(SO(3))] x 8 H(2)O, Ln = La(3+) (1), Sm(3+) (2), and Ce(3+) (3). The title compounds have been characterized by elemental analyses, IR, diffuse reflectance, electron paramagnetic resonance, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and single-crystal X-ray diffraction studies. All three compounds crystallize in the monoclinic space group P2(1)/n. Crystal data for 1: a = 13.4839(7), b = 12.3388(6), c = 18.3572(10) A, beta = 108.2570 (10) degrees, V = 2900.4(3) A(3). Crystal data for 2: a = 13.4156(3), b = 12.2588(3), c = 18.2501(4) A, beta = 108.049(3) degrees, V = 2853.8(10) A(3). Crystal data for 3: a = 13.4934(3), b = 12.3983(3), c = 18.3992(4) A, beta = 108.025(3), V = 2927.0(10) A(3). Crystal structure shows that each cluster is surrounded by six [Ln(H(2)O)(6)](3+) complex cations, and each [Ln(H(2)O)(6)](3+) cation is coordinated to three surrounding POV cluster anions. The electron spin resonance spectra of compounds 1-3 show a typical single line (g = 1.9671 for 1, g = 1.9669 for 2, and g = 1.9704 for 3), characteristic for a V(4+) (d(4)) ion; in addition, a supplementary signal appears for compound 2 at g = 5.9238 due to the presence of the Sm(3+) (f(5)) ion. All vanadium atoms exit in +4 oxidation states that have been confirmed by bond valence sum calculations. Variable-temperature magnetic studies for all three compounds 1-3 are performed and are discussed in terms of antiferromagnetic coupling interactions, giving importance to linking/assembling the {V(14)} cluster anions. TGA/mass analyses of compounds 1-3 (linked system) have been compared with that of the starting precursor [NH(4)](6)[As(8)V(14)O(42)(SO(3))] (discrete building unit). Interestingly, the evolution of SO(2) gas takes place for the discrete cluster compound [NH(4)](6)[As(8)V(14)O(42)(SO(3))] in a temperature range of 480-520 degrees C with the decomposition of the POV cluster anion, whereas the same evolution occurs at 520-580 degrees C for compounds 1-3. These comparative TGA/mass studies help to understand how the organic free linker elevates the thermal stability of the sulfite encapsulated POV cluster anion in going from a discrete cluster anion to the linked system (molecule to material). It has also been demonstrated that the stability of the sulfite anion increases to a greater extent when it is included in the cluster cage. The powder XRD studies of compounds 1-3 confirm that these are isostructural materials and provide information about the phase purity.

In Situ Ligand Reactions under Hydrothermal Conditions Afford a Novel Zinc-Substituted Polyoxovanadate Dimer

A novel polyoxovanadate (POV), [Zn(2,2'-bpy)3]4[(ppz){{Zn(tepa)}2ZnAs8V13O41(H2O)}2][As8V14O42(0.5H2O)]2.4H2O (1, 2,2'-bpy = 2,2'-bipyridine, ppz = piperazine, tepa = tetraethylenepentamine), has been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectra, thermogravimetric analysis, magnetic measurement, and single-crystal X-ray diffraction analysis. Crystal data for 1: orthorhombic, Aba2, a = 28.3414(14) A, b = 27.9995(16) A, c = 41.5819(16) A, V = 32997(3) A3, Z = 4, rho = 2.264 mg.cm-3. X-ray structure analysis shows that the structure of 1 consists of one unique zinc-substituted POV dimer and two POV monomers. Interestingly, the formation of the zinc-substituted POV dimer involves two new in situ ligand reactions under hydrothermal conditions, the intermolecular and intramolecular deamination coupling reactions of dien. Magnetization measurement revealed the presence of antiferromagnetic interaction between V(IV) ions in 1.

Investigating lithium ion conductivity in amorphous solids containing [V10O28]6− clusters by computer simulation

Computer simulation method was applied to investigate the migration of lithium ion in three amorphous solid systems containing polyoxovanadate (POV) clusters [V10O28]6 − . The cluster was adopted from a recently synthesized crystalline poly[octa-μ-aqua-octaaqua-μ-decavanadato-hexalithium] (POAODH). The simulated POV systems correspond to amorphous solid half-dehydrated solid and completely dehydrated solid doped with LiCl salt. The simulation results show large diffusion constants of lithium ions in all systems in spite of highly negatively charged [V10O28]6 − clusters presented in the system. The estimated ionic conductivity due to the migration of lithium ions reaches a magnitude of 10− 4 S/m. The conductivity increases as the water content in the system decreases. The analysis of moving trajectories shows the lithium ion moves around the oxygen sites of POV clusters and hops between them. The estimated displacement of lithium ion is about 4∼5 Å, which is much larger than the corresponding displacement of lithium ion in a polymer matrix. Rapidly rotating clusters shown by orientation correlation function analysis, in conjunction with the large separation between clusters in the system, provides favorable conditions for the large amplitude migration of lithium ions.

A Highly Reduced Vanadium(III/IV) Polyoxovanadate Comprising an Octavanadyl Square-Prism Surrounding a Dimetallic Vanadium(III) Fragment

The synthesis, crystal structure and preliminary magnetic studies are reported for a very highly reduced, VIV8VIII2, polyoxo(alkoxo)vanadate with a unique square prismatic topology.