Vanadium Centers Research Articles

Exploring the Magnetic Interaction of Asymmetric Structures Based on Chiral VIII8 Clusters.

Polyoxovanadates (III) are important class of polyoxometalates in molecular magnetism field, and particularly the systems which contain vanadium(III) centers. To date, only very few highly reduced vanadium polynuclear complexes were reported, which remains a significant challenge to synthesize novel polyoxovanadates, owing to the characteristics of easily oxidized vanadium(III). Herein, two unprecedented petaloid chiral octanuclear polyoxovanadates, l- and d-[H2N(CH3)2]12.5(H3N(CH2)2NH3)(H3O)1.5(VIIIμ2-OH)8(SO4)16·2H2O (L-, D-V8), have been successfully obtained by solvothermal method without any chiral auxiliary. Both L- and D-V8 compounds contain the motif eight-membered ring (Vμ2-O)8(SO4)16 constituted of three different chiral entangled loops with the V atoms as nodes. Bond valence calculation (BVC) analysis indicates that all the V ions existed in L, D-V8 are +3 value. The magnetic behavior of compounds indicated ferromagnetic coupling between vanadium(III) ions. To our knowledge, it is the first chiral highly reduced polyoxovanadates that exhibit excellent ferromagnetism.

Probing the chirality of oxidovanadium(v) centers in complexes with tridentate sugar Schiff-base ligands: solid-state and solution behavior

Configurations of oxidovanadium centers in diastereomeric complexes with chiral sugar ligands are assigned and in the solid state triggered by the coordination number at the vanadium center through the steric requirements of the chelate ligand.

Vanadium(V) oxide clusters synthesized by sublimation from bulk under fully inert conditions.

Oxide nanoparticles in the size range of a few nanometers are typically synthesized in solution or via laser ablation techniques, which open numerous channels for structural change via chemical reactions or fragmentation processes. In this work, neutral vanadium oxide nanoparticles are instead synthesized by sublimation from bulk in combination with a pickup by superfluid helium droplets. Mass spectroscopy measurements clearly demonstrate the preservation of the bulk stoichiometric ratio of vanadium to oxygen in He-grown nanoparticles, indicating a tendency towards tetrahedral coordination of the vanadium centers in finite geometries. This unexpected finding opens up new possibilities for a combined on-the-fly synthesis of nanoparticles consisting of metal and metal-oxide layers. In comparison to mass spectra obtained via direct ionization of vanadium oxide in an effusive beam, where strong fragmentation occurred, we observe a clear preference for (V2O5) n oligomers with even n inside the He nanodroplets, which is further investigated and explained using the electronic structure theory.

A series of new vanadium(iii) chalcogenido-antimonates: an unusual seven-coordinate nitro-selenidovanadium(iii) complex.

A series of new vanadium(iii) chalcogenidoantimonates [VIII(dap)2SbQ3] (Q = S (1), Se (2); dap = 1,2-diaminopropane), [H2dien][VIII2(en)2(dien)2(μ2-O)][SbSe4]2 (3, en = ethylenediamine; dien = diethylenetriamine) and [VIII(dien)2SbSe4] (4) have been solvothermally synthesized and structurally characterized. Both 1 and 2 contain neutral vanadium(iii)-centered complexes [VIII(dap)2SbQ3], where the [SbQ3]3- anion acts as a chelating ligand to complex [VIII(dap)2]3+, but they exhibit different molecular conformations. 3 consists of selenidoantimonate anions [SbSe4]3-, the protonated H2dien2+ cation, and the dinuclear complex [VIII2(en)2(dien)2(μ2-O)]4+ based on two [VIII(en)(dien)]3+ units bridged by one μ2-O group. 4 contains neutral [VIII(dien)2SbSe4] moieties with seven coordinated vanadium centres, which offers a rare example of high coordination of a nitro-selenidovanadium(iii) complex, mainly because the vanadium(iii) ion has a regular octahedral configuration based on the structures in the solid state. The optical, magnetic and photoelectronic properties of all compounds have been investigated, and the density functional theory calculation of 4 has also been studied.

In vitro apoptosis-induction, antiproliferative and BSA binding studies of a oxidovanadium(V) complex

In our ongoing efforts to develop novel trace metal complexes with therapeutically interesting properties, a neutral mono nuclear oxidomethoxidovanadium(V) complex, [VVO(OCH3)(hpdbal-sbdt)] (1) and a μ-O bridged dinuclear oxidovanadium(V) complex, [{VVO(hpdbal-sbdt)}2μ−O] (2) [H2hpdbal-sbdt (I) is a tridentate and dibasic ONS2― donor ligand obtained through the Schiff base reaction of 2-hydroxy-5-(phenyldiazenyl)benzaldehyde (Hhpdbal) and S-benzyldithiocarbazate (Hsbdt)] have been synthesized and characterized by various analytical techniques such as TGA, EDS, ATR-IR, UV–Vis, CV, 1H NMR, 13C NMR and 51V NMR. Single-crystal X-ray diffraction analysis of 1 confirms the coordination of phenolate oxygen, imine nitrogen and thioenolate sulfur of the ligand to the vanadium center with a distorted tetragonal-pyramidal geometry. The compound 2 triggered apoptotic and reproductive death of the cancer cells in vitro with 76% and 62% growth inhibition of human breast adenocarcinoma (MCF-7) and human lung carcinoma cells (A549) respectively. The compound 2 was found to be sufficiently stable over a wide window of physiological pH. The complex 2 was studied further for its interaction with a drug carrier protein BSA with the aid of spectroscopic techniques viz. fluorescence, temperature controlled UV–vis and deconvoluted IR techniques.

Synthesis, Characterization and Bioactivities of Some Novel Oxovanadium(IV) Glycinato Complexes

The novel oxovanadium(IV) complexes, [VIVO(GlyH)(Gly)]+ClO4 - .H2O (1), [VIVO(GlyH)(Gly)]+NO3 - .H2O (2), [VIVO(GlyH)(Gly)]+CH3COO- .H2O (3) were synthesized and characterized by FT-IR, UV-Vis and 1H NMR spectroscopic measurements. The cumulative spectroscopic assessment envisaged that, the complexes adopt a square pyramidal structure, in which the two glycine ligands coordinate to vanadium(IV) center in bidentate fashions conforming a homoleptic structure. The amino nitrogen and a carboxylato oxygen atom coordinate the vanadium(IV) center from both sides making a five members chelate by each side. All the complexes are stable in amorphous state and in aerobic and anaerobic solution. Significantly, all the complexes have the antifungal activities against Aspergillus niger and Penicillium notatum but ineffective against Candida tropicalis. No antibacterial activity was observed for the complexes against tested bacteria and unfortunately, they were found cytotoxic against brine shrimp bioassay.

Activation mechanism of hydrogen peroxide by a divanadium–substituted polyoxometalate [γ–PV2W10O38(μ–OH)2]3–: A computational study

In the present paper, the reaction mechanism corresponding to activation of hydrogen peroxide (H2O2) by a divanadium–substituted polyoxometalate (POM) [γ–PV2W10O38(μ–OH)2]3– (I) to form catalytic active species, peroxo complex [γ–PV2W10O38(μ-η2,η2–O2)]3– (III), was studied by using the density functional theory (DFT) calculations method with B3LYP functional. The results indicate that coordination of H2O2 to I proceeds via a vanadium–center–assisted proton transfer pathway to remove the first water molecule and form a hydroperoxy intermediate [γ–PV2W10O38(μ–OH) (μ–OOH)]3– (II). And intermediate II occurs through three successive water–assisted proton transfer steps to remove the second water molecule and finally forms catalytic active species. The calculated overall energy profiles show that coordination of H2O2 to vanadium center requires a proton transfer barrier of about 24 kcal mol−1. A detailed comparison of molecular geometries and electronic structure shows that the catalytic active species has a very interesting structural feature, where a superoxide radical (O2−) was embedded into two vanadium centers, and may be a potential nucleophile. The unique withdrawing electron properties and flexible bonding ability of the γ–Keggin–type POM ligand contribute to the formation of O2− radical. The tunable alternate arrangement of W–O bond series in γ–Keggin–type POM ligand contributes to the flexibility of the γ–Keggin–type POM ligand. Meanwhile, our DFT calculations show a good performance of B3LYP-gauge-independent atomic orbital (IGAIM) method for the calculation of 1H NMR parameters of divanadium-substituted phosphotungstate.

Efficient oxidative dehydrogenation of ethanol by VOx@MIL-101: On par with VOx/ZrO2 and much better than MIL-47(V)

The possibility to apply metal organic framework (MOF) based catalysts for oxidation reaction in gas phase was explored. Catalytic activity of the vanadium oxide catalyst incorporated in MIL-101(Cr) as support was investigated in gas phase ethanol oxidative dehydrogenation (EtOH-ODH) and compared to that of MIL-47(V) metal organic framework material containing vanadium as central metal in the framework structure and to a classical VOx/ZrO2 supported vanadium oxide catalyst. It was found that vanadium species, incorporated in MIL-101(Cr) support by a variant of vapor deposition method, are stabilized in the form of well dispersed VOx species (no vanadium pentoxide clusters was detected in the catalyst). The obtained VOx@MIL-101(Cr) catalyst exhibited high selectivity towards acetaldehyde (up to 99%) at reaction temperatures not exceeding 200 °C. The catalytic activity of VOx@MIL-101(Cr) catalyst reached an activity level comparable to that of the classical VOx/ZrO2 catalyst, but the specific productivity of acetaldehyde (3 kgAA kgcat−1 h−1) was higher by 75% compared with productivity on VOx/ZrO2 due to much higher content of vanadium species, which could be hosted by the MOF. On the other hand, MIL-47(V) catalyst exhibited negligible activity seemingly due to coordinatively saturated character of the vanadium centers and/or too high stability of the VIV oxidation state. This proof-of-concept study proved that application of MOF materials as host matrices for heterogeneous catalysts aiming oxidation reaction in gas phase could be efficient as demonstrated on the example of oxidative dehydrogenation of ethanol.

Chemisorption of NH3 on Monomeric Vanadium Oxide Supported on Anatase TiO2: A Combined DRIFT and DFT Study

V/TiO2 catalysts are used in various reactions, including oxidative dehydrogenation, partial oxidation of ethanol, and selective catalytic reduction of NOx with NH3. In this work, we investigated the effect of supported monomeric vanadium oxide (VO3) on the acidity of anatase TiO2(101) surface by using density functional theory calculations combined with in situ diffuse reflectance infrared Fourier transform (DRIFT) experiments. The hydrogenation of TiO2 to form hydroxyl groups on the surface was energetically more favorable in the presence of the supported monomeric vanadium oxide. Charge transfer between TiO2 support and VO3 was considered as an origin of −OH stabilization, which made Bronsted acid sites more abundant on the V/TiO2 surface than on TiO2. Moreover, it was observed that the cationic vanadium center in VO3 can act as much weaker Lewis acid sites than the titanium center in TiO2. Such weakened acidity of Lewis acid sites in the presence of monomeric vanadium oxide was consistently observed i...

Properties, structure and stability of V(IV) hydrazide Schiff base ligand complex

The reaction of vanadyl sulfate, VOSO4·H2O, with Schiff base ligand based on 2-hydroxybenzhydrazide and 5-bromosalicylaldehyde, with addition of 1,10-phenantroline as co-ligand, in ethanolic solution results in isolation of oxovanadium(IV) complex [VO(phen)L]·H2O (1). The complex was characterized by elemental analysis, single crystal X-ray structure measurements, IR, UV–Vis, EPR spectroscopy and cyclic voltammetry. Magnetic susceptibility measurements indicated the +4 vanadium oxidation state. The molecular structure of the complex was confirmed by single-crystal X-ray diffraction, revealing that the central vanadium atom was located in a six-coordinate distorted octahedral geometry. The stability of the complex at native pH and pH = 2.00 was also measured and the results are promising for application the vanadium complex as insulin mimetic compound.

Investigations of the Magnetic and Spectroscopic Properties of V(III) and V(IV) Complexes.

Herein, we utilize a variety of physical methods including magnetometry (SQUID), electron paramagnetic resonance (EPR), and magnetic circular dichroism (MCD), in conjunction with high-level ab initio theory to probe both the ground and ligand-field excited electronic states of a series of V(IV) ( S = 1/2) and V(III) ( S = 1) molecular complexes. The ligand fields of the central metal ions are analyzed with the aid of ab initio ligand-field theory (AILFT), which allows for a chemically meaningful interpretation of multireference electronic structure calculations at the level of the complete-active-space self-consistent field with second-order N-electron valence perturbation theory. Our calculations are in good agreement with all experimentally investigated observables (magnetic properties, EPR, and MCD), making our extracted ligand-field theory parameters realistic. The ligand fields predicted by AILFT are further analyzed with conventional angular overlap parametrization, allowing the ligand field to be decomposed into individual σ- and π-donor contributions from individual ligands. The results demonstrate in VO2+ complexes that while the axial vanadium-oxo interaction dominates both the ground- and excited-state properties of vanadyl complexes, proximal coordination can significantly modulate the vanadyl bond covalency. Similarly, the electronic properties of V(III) complexes are particularly sensitive to the available σ and π interactions with the surrounding ligands. The results of this study demonstrate the power of AILFT-based analysis and provide the groundwork for the future analysis of vanadium centers in homogeneous and heterogeneous catalysts.

Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and μ-Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X-ray Structure, Magnetic Properties, and Cytotoxicity.

The synthesis of ethoxido-bridged dinuclear oxidovanadium(IV) complexes of the general formula (HNEt3)[(VOL1-3)2(μ-OEt)] (1-3) with the azo dyes 2-(2'-carboxy-5'-X-phenylazo)-4-methylphenol (H2L1, X = H; H2L2, X = NO2) and 2-(2'-carboxy-5'-Br-phenylazo)-2-naphthol (H2L3) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of 1 and 3 revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium(IV) complexes (1-3) were cytotoxic in nature and were specific to a particular cell type. Complex 1 was found to be the most potent against HeLa cells (IC50 value 1.92 μM).

Effects of the Heat Treatment on the Photoluminescence Properties for La1-XPrxVO4 Phosphor Prepared by a Hydrothermal Method

A hydrothermal method had been employed firstly for the preparation of La1-xPrxVO4 (x=0—0.05) nano-crystal phosphors, and then they were annealed at 600 oC for 4 h. The x-ray diffraction profiles show that the La1-xPrxVO4 phosphors still keep the tetragonal structure. The SEM results show that phosphor particles were increased from 60 nm to 80 nm after annealing process, and the surface morphology gradually changed from reunion to uniform distribution. The excitation spectra show that an absorption band between 200 ~ 330 nm is due to the charge transfer from the oxygen ligands to the central vanadium atom inside the VO4 3- anionic group, and the Pr3+ ion 4f-5d characteristic transition is located between in the 440 ~ 500 nm and 580 ~ 620 nm region. By 315 nm excitation, the main emission band still retains the characteristics for Pr3+ ion-doped LaVO4 phosphor, belonging to the host luminescent, and the 1D2→3H4, 3P0→3H6 electron transition of the Pr3+ ion, respectively. As the Pr3+ ion concentration increases, the color tone changes from blue ( 0 mol% Pr3+ ion doping ) to white (for 0.2-1 mol% Pr3+ ion doping), to blueish (for 5 mol% Pr3+ ion doping). Therefore, the color of the emission for (Y1-xPrx)InGe2O7 phosphors can be tuned by adjusting the Pr3+ ion concentration, without doping other color centers in a single phased host lattice. When the Pr3+ ion concentration of x=0.005, it possesses the strongest emission behavior, and is located in the white light region with a CIE chromaticity coordinates of x=0.299, y=258.

Experimental and theoretical studies on vanadium bromoperoxidase activity of alkyne arm dioxidovanadium(V) complex: Crystal structure, spectral studies, and DFT calculations

The alkyne arm bearing dioxidovanadium(V) complex was synthesized by the reaction of vanadium sulphate, 1-[2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl]ethanone and propane-1,2-diamine. The synthesized complex was characterized by various spectral techniques and its structure was determined using single-crystal X-ray diffraction analysis. Vanadium centre has square-pyramidal based geometry with an axial oxido ligand and the equatorial positions are occupied by another oxido ligand and phenolato oxygen, imine nitrogen and free amine nitrogen atoms. DFT and TD-DFT calculations were examined to identify the electronic structure, and electronic transitions of the complex observed in the absorption spectra. The percentage of intermolecular interactions in the crystal structure has been evaluated by 3D Hirshfeld surfaces and 2D fingerprint plots. The CH⋯π and intermolecular interactions of the complex were examined using Bader’s theory of QTAIM by ADF 2017. The dioxidovanadium(V) complex mimics as an efficient vanadium-dependent bromoperoxidase towards the bromination of phenol red in acetonitrile medium at room temperature.

Mononuclear oxidodiperoxido vanadium(V) complex: synthesis, structure, VHPO mimicking oxidative bromination, and potential detection of hydrogen peroxide

An oxidodiperoxidovanadium(V) complex, (NH4)[VO(O2)2(phen)](H2O)2, has been synthesized and structurally characterized. The complex crystallizes in the P21/c space group. The vanadium center is seven-coordinate with pentagonal bipyramidal geometry. The compound was designed in order to develop a VHPO mimic, so it was tested for VHPO activity through the single pot bromination of phenol red to bromophenol blue whereby, it afforded positive response to establish that the complex is indeed a VHPO mimic. In addition, the compound is capable of detection of H2O2.

Stabilization of a Metastable Tunnel‐Structured Orthorhombic Phase of VO2 upon Iridium Doping

Metastable compounds accessible through kinetic stabilization or under conditions of constrained equilibrium represent a richly varied landscape of structures, properties, and function that are oftentimes entirely inaccessible in thermodynamic minima. The multiple redox states of vanadium and the ability to modulate the connectivity of vanadium and oxygen atoms yields a rich diversity of structures for binary vanadium oxides. Here, it is demonstrated that an orthorhombic quasi‐1D polymorph of VO2, characterized by extended tunnels with a rectangular cross‐section, can be stabilized through the substitutional doping of iridium on the vanadium sublattice. The obtained structure is considerably distorted from a previously reported paramontroseite mineral phase. The metastable phase is obtained in nanoplatelet form and is stable with respect to the energetically proximate monoclinic/rutile thermodynamic minima up to a temperature of 350 °C. The open framework structure and the accessibility of multiple redox states at the vanadium center suggests that the polymorph could potentially serve as an intercalation host. Beyond the solubility limit of iridium on the vanadium sublattice (1.28–3.15 at.% depending on the precursor concentration), metallic Ir nanocrystals are found to be homogeneously dispersed on the surfaces of the nanoplatelets indicating a strong interaction between the metal nanocrystals and oxide lattice.

Modeling Polaron-Coupled Li Cation Diffusion in V2O5 Cathode Material

The transport of intercalated Li cations in oxide materials comprises two aspects, ion diffusion and migration of an associated small polaron. We examined computationally these two aspects of Li transport in vanadium pentoxide (V2O5) cathode material in a consistent fashion, using a DFT+U approach. Exploring various migration scenarios at low Li concentrations, we determined barriers of ∼0.3 eV, mostly due to polaron migration. In consequence, intercalating Li atoms, at low concentrations, migrate in the interlayer region of V2O5 as quasi-particles where Li cations remain closely associated with their valence electrons, where a small polaron structure forms around the reduced vanadium center.

How the distribution of reduced vanadium centers affects structure and stability of the MoVOxmaterial

The energy ordering of configurations, with 6 among the 10 V centers reduced, is predicted using 3 easily accessible variables.

Design and Performance of Rechargeable Sodium Ion Batteries, and Symmetrical Li‐Ion Batteries with Supercapacitor‐Like Power Density Based upon Polyoxovanadates

AbstractThe polyanion Li7V15O36(CO3) is a nanosized molecular cluster (≈1 nm in size), that has the potential to form an open host framework with a higher surface‐to‐bulk ratio than conventional transition metal oxide electrode materials. Herein, practical rechargeable Na‐ion batteries and symmetric Li‐ion batteries are demonstrated based on the polyoxovanadate Li7V15O36(CO3). The vanadium centers in {V15O36(CO3)} do not all have the same VIV/V redox potentials, which permits symmetric devices to be created from this material that exhibit battery‐like energy density and supercapacitor‐like power density. An ultrahigh specific power of 51.5 kW kg−1 at 100 A g−1 and a specific energy of 125 W h kg−1 can be achieved, along with a long cycling life (>500 cycles). Moreover, electrochemical and theoretical studies reveal that {V15O36(CO3)} also allows the transport of large cations, like Na+, and that it can serve as the cathode material for rechargeable Na‐ion batteries with a high specific capacity of 240 mA h g−1 and a specific energy of 390 W h kg−1 for the full Na‐ion battery. Finally, the polyoxometalate material from these electrochemical energy storage devices can be easily extracted from spent electrodes by simple treatment with water, providing a potential route to recycling of the redox active material.

DNA/BSA binding interactions and VHPO mimicking potential of vanadium(IV) complexes: Synthesis, structural characterization and DFT studies

Vanadium(IV) Schiff base complexes (VOL1‐VOL3) were synthesized and characterized by elemental analysis, various spectral methods and single crystal XRD studies. Structural analysis of VOL2 reveals that the central vanadium ion in the complex is six coordinate with distorted octahedral geometry. Density functional theory (DFT) and time dependent (TD‐DFT) studies were used to understand the electronic transitions observed in the complexes in UV–Vis spectra. The electrochemical behavior of the complexes was investigated in acetonitrile medium exhibit quasi‐reversible one electron transfer. The DNA and BSA protein binding interaction of vanadium complexes has been explored by UV–Vis and fluorescence spectral methods and viscosity measurements reveal that the complexes interact with CT‐DNA through intercalation mode and follows the order VOL1 < VOL3 < VOL2. The complexes exhibit binding interactions with BSA protein. The complexes act as chemical nuclease and cleave DNA in the presence of H2O2. The 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assay was used to evaluate the radical scavenging activity demonstrate the antioxidant property of the complexes. The antimicrobial activity was screened for several microorganisms, Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli. The mimicking of vanadium haloperoxidase was investigated by the bromination of the organic substrate phenol red by vanadium complexes in the presence of bromide and H2O2.