Tungsten Clusters Research Articles

Water-soluble neutral octahedral chalcogenide tungsten and molybdenum {M6Q8} clusters with P(C2H4CONH2)3 ligand

Developing the chemistry of octahedral chalcogenide molybdenum and tungsten cluster complexes in the context of applications in biology and medicine, in this work a series of water-soluble neutral cluster complexes [{M6Q8}(P(C2H4CONH2)3)6] (M = Mo, W; Q = S, Se) have been obtained by simultaneous replacement of inner and terminal halide ligands in [{M6I8}I6]2− with chalcogenide and organic phosphine ligands and characterized by single-crystal X-ray diffraction analysis, 1H and 31P NMR spectroscopies, elemental analysis, and UV–vis spectroscopy. The amide groups of the organic ligands, on the one hand, contribute to the solubility of the resulting clusters in water and, on the other hand, are able to form an extensive network of hydrogen bonds, leading to the crystallization of the complexes from aqueous solutions. Despite this fact, the complexes have sufficient solubility and stability in aqueous solutions, which made it possible to demonstrate their low cytotoxicity on Hep-2 cells (IC50 were not reached even at concentration up to 4 mM). The resulting clusters are among the most biocompatible of the octahedral clusters studied to date and are the starting point for the development of a new family of X-ray contrast agents.

Iodide clusters of molybdenum and tungsten as promising agents for photodynamic inactivation and therapy

Iodide clusters of molybdenum and tungsten as promising agents for photodynamic inactivation and therapy

Surface Electroactive Sites of Tungstated Zirconia Catalysts for Vanadium Redox Flow Batteries.

Surface electroactive sites for tungstate zirconia (WZ) were created by utilizing tungstate-immobilized UiO-66 as precursors via a double-solvent impregnation method under a mild calcination temperature. The WZ-22-650 catalyst, containing a moderate W content (22%), demonstrated a high density of surface electroactive sites. Proper heat treatment facilitated the binding of oligomeric tungsten clusters to stabilized tetragonal ZrO2, resulting in improved catalytic performance toward the VO2+/VO2+ redox couples compared to other tested samples. The substantial surface area, mesoporous structure, and establishment of new W-O-Zr bonds affirm the firm anchoring of WOx to ZrO2. This robust attachment enhances surface electroactive sites, elevating the electrochemical performance of vanadium redox flow batteries (VRFBs). Charge-discharge tests further demonstrate that the superior voltage efficiency (VE) and energy efficiency (EE) for VRFBs using the WZ-22-650 catalyst are 87.76 and 83.94% at 80 mA cm-2, which are 13.42% VE and 10.88% EE better than heat-treated graphite felt, respectively. Even at a higher current density of 160 mA cm-2, VRFBs utilizing the WZ-22-650 catalyst maintained considerable efficiency, recording VE and EE values of 76.76 and 74.86%, respectively. This facile synthesis method resulted in WZ catalysts displaying superior catalytic activity and excellent cyclability, offering a promising avenue for the development of metal-oxide-based catalysts.

A double-tartrate-bridged deca-nuclearity europium-tungsten cluster embedded selenotungstate and its selective optical sensing of o-nitrophenol

A double-tartrate-bridged deca-nuclearity europium-tungsten cluster embedded selenotungstate and its selective optical sensing of o-nitrophenol

Femtosecond laser thinning for resistivity control of tungsten ditelluride thin-films synthesized from sol-gel deposited tungsten oxide

In this work we present a route for fabricating WTe2 thin-films together with femtosecond laser post processing, enabling to finely control the conductivity. First, we produce amorphous films of WO3 on Si by spin-coating a sol-gel precursor followed by a consolidating annealing and a reduction process in partial H2 atmosphere, leading to porous metallic tungsten cluster layers. To achieve WTe2, the films were exposed to the chalcogen vapours by isothermal closed space vapor transport. The formation of a tungsten ditelluride film composed of piled crystals could be confirmed and a gradient of surface rich Te identified through hard X-ray photoelectron spectroscopy. Finally, it is demonstrated that resistivity can be changed from 0.2 mΩ.m to 1 mΩ.m, while keeping the material characteristics. An anisotropic conductivity can be induced by direct selective thinning with fs laser writing (350 fs pulse duration, 515 nm laser wavelength) of 1D stripes. The obtained results, demonstrate that laser processing is a promising thin-film post-processing technique that can be applied to 2D transition metal dichalcogenide thin films.

Tungsten clusters derived from phosphotungstic acid to enhance hydrogen storage efficiency in MgH2

MgH2 has a high hydrogen storage capacity but suffers from high operating temperature and slow dehydrogenation kinetics due to the strong Mg–H bond. Here, phosphotungstic acid are molecularly loaded on the surface of MgH2 submicron particles and then further reduced to tungsten clusters with size of ∼2 nm during hydrogen uptake/release operation. The tungsten clusters act as catalysts to reduce the dehydrogenation temperature and activation energy of MgH2 by 36 °C and 15 kJmol-1, respectively. W cluster-decorated MgH2 can release more than 6 wt% hydrogen in 30 min at 300 °C; even at 250 °C, the material can still absorb 6 wt% hydrogen in a few minutes and release 4 wt% hydrogen in 1 h, outperforming previously reported W-based catalysts (micro/submicron WO3 and WS2). In addition, this material also shows stable cycling performance. This study demonstrates promising prospects of polyoxometalates as efficient catalysts for hydrogen storage materials.

Reactions of Triangular Molybdenum and Tungsten Clusters with Tetrabromocatechol

Reactions of Triangular Molybdenum and Tungsten Clusters with Tetrabromocatechol

Reactions of Triangular Molybdenum and Tungsten Clusters with Tetrabromocatechol

The reaction of cluster complex (nBu4N)2[Mo3Se7Br6] with tetrabromocatechol (H2Tbc) in the presence of Et3N and Ph4PBr results in the formation of (Ph4P)2[Mo3Se7(Tbc)3]∙2MeOH (Ia∙2MeOH). Under the same conditions, the tungsten analogue (nBu4N)2[W3S7Br6] is completely or partly destroyed to give the complex (Ph4P)(Et3NH)[WO2(Tbc)2] (II). The structures of Ia·2MeOH and II were established by X-ray diffraction analysis (CCDC nos. 2213900 and 2213901, respectively). The redox properties of complex Ia and related (Ph4P)2[Mo3S7(Tbc)3] (Ib) and (Ph4P)2[Mo3S7(Tcc)3] (Ic) (Tcc is tetrachlorocatecholate) were also studied by cyclic voltammetry.

Multifunctional Oxidized Dextran as a Matrix for Stabilization of Octahedral Molybdenum and Tungsten Iodide Clusters in Aqueous Media.

Due to their high abundance, polymeric character, and chemical tunability, polysaccharides are perfect candidates for the stabilization of photoactive nanoscale objects, which are of great interest in modern science but can be unstable in aqueous media. In this work, we have demonstrated the relevance of oxidized dextran polysaccharide, obtained via a simple reaction with H2O2, towards the stabilization of photoactive octahedral molybdenum and tungsten iodide cluster complexes [M6I8}(DMSO)6](NO3)4 in aqueous and culture media. The cluster-containing materials were obtained by co-precipitation of the starting reagents in DMSO solution. According to the data obtained, the amount and ratio of functional carbonyl and carboxylic groups as well as the molecular weight of oxidized dextran strongly affect the extent of stabilization, i.e., high loading of aldehyde groups and high molecular weight increase the stability, while acidic groups have some negative impact on the stability. The most stable material based on the tungsten cluster complex exhibited low dark and moderate photoinduced cytotoxicity, which together with high cellular uptake makes these polymers promising for the fields of bioimaging and PDT.

Improved Synthesis of (TBA)2[W6Br14] Paving the Way to Further Study of Bromide Cluster Complexes.

Octahedral cluster complexes of molybdenum and tungsten, [M6X8Y6]n- (M = Mo, W; X, Y = Cl, Br, I), are promising active components in various fields, including biomedicine and solar energy. Cluster complexes draw considerable attention due to their X-ray opacity, red/near-IR luminescence, and ability to convert triplet molecular oxygen to active singlet oxygen under UV and visible irradiation. Among the octahedral cluster complexes of molybdenum and tungsten, compounds with a {W6Br8}4+ core are the least studied. There are only a few examples of compounds with substituted terminal ligands, and their properties are not well understood. Among other things, this is due to more labor-intensive and expensive methods for obtaining the starting compounds in comparison with molybdenum counterparts. In this paper, we describe the synthesis of an octahedral cluster complex, (TBA)2[W6Br14] (TBA+ = tetrabutylammonium), in gram quantities, starting from simple substances─W, Br2, and Bi─in 70% yield. The formation of pentanuclear tungsten cluster complexes was recorded as a byproduct. Compounds with substituted terminal ligands (TBA)2[W6Br8Y6] (Y = NO3, Cl, I) were obtained. We also discuss the instability of (TBA)2[W6Br8(NO3)6] under light exposure, the optical properties of a series of compounds (TBA)2[W6Br8Y6] (Y = Cl, Br, I), and the effect of terminal ligands on the chemical shifts in 183W NMR spectra in dimethyl sulfoxide-d6. The presented approach to the synthesis of one of the main precursors of various bromide cluster complexes on a gram scale can stimulate the study of their properties and development of new functional materials based on them.

Oxygen-Sensitive Photo- and Radioluminescent Polyurethane Nanoparticles Modified with Octahedral Iodide Tungsten Clusters.

The development of cancer treatment techniques able to cure tumors located deep in the body is an urgent task for scientists and physicians. One of the most promising methods is X-ray-induced photodynamic therapy (X-PDT), since X-rays have unlimited penetration through tissues. In this work, octahedral iodide tungsten clusters, combining the properties of a scintillator and photosensitizer, are considered as a key component of nanosized polyurethane (pU) particles in the production of materials promising for X-PDT. Cluster-containing pU nanoparticles obtained here demonstrate bright photo- and X-ray-induced emission in both solid and water dispersion, great efficiency in the generation of singlet oxygen, and high sensitivity regarding photoluminescence intensity in relation to oxygen concentration. Additionally, incorporation of the cluster complex into the pU matrix greatly increases its stability against hydrolysis in water and under X-rays.

Relativistic versus Jahn-Teller effects in tantalum and tungsten clusters

We juxtapose the interplay of relativistic and Jahn-Teller effects in small tantalum and tungsten clusters. We employ relativistic techniques to study the low-lying electronic states of Tan for 2 ≤ n ≤ 6. We have used the complete active space MCSCF (CASSCF) techniques for the low-lying electronic states of Ta2 together with DFT techniques including spin–orbit corrections for large clusters that employed relativistic effective core potentials. The results thus obtained were compared with CASSCF/MRCI computations together with the inclusion of spin–orbit coupling for the tungsten trimer. Our computations reveal that unlike clusters containing lighter atoms, the spin–orbit effects overcome Jahn-Teller stabilization effects resulting in more symmetrical structures for tantalum and tungsten clusters. We have also computed the 3D-potential energy surfaces of different interesting regions of the Mexican hat surfaces. Whereas for the trimer and tetramer spin–orbit stabilization seems to overtake Jahn-Teller stabilization, thus resulting in the stabilization of symmetric structures, the Jahn-Teller stabilizations are larger than spin–orbit effects for larger clusters, thus resulting in distorted structures for larger clusters. We have provided a double group and graph-theoretical analysis of the electronic states of tantalum clusters to gain insights into the effect of spin–orbit coupling and pseudorotation on the electronic states of these clusters. The absorption spectra for these clusters are computed using time dependent density functional theory (TDDFT).

Water-Soluble Chalcogenide W6-Clusters: On the Way to Biomedical Applications.

Despite the great potential of octahedral tungsten cluster complexes in fields of biomedical applications such as X-ray computed tomography or angiography, there is only one example of a water-soluble W6Q8-cluster that has been reported in the literature. Herein we present the synthesis and a detailed characterization including X-ray structural analysis, NMR, IR, UV–Vis spectroscopies, HR-MS spectrometry, and the electrochemical behavior of two new cluster complexes of the general formula W6Q8L6 with phosphine ligands containing a hydrophilic carboxylic group, which makes the complexes soluble in an aqueous medium. The hydrolytic stability of the clusters’ aqueous solutions allows us to investigate for the first time the influence of W6-clusters on cell viability. The results obtained clearly demonstrate their very low cytotoxicity, comparable to the least-toxic clusters presented in the literature.

Nonoxidative coupling of methane to olefins and aromatics over molten W-In bimetal catalyst

Direct nonoxidative conversion of methane to ethylene, aromatics and hydrogen has been recognized as an attractive utilization of natural gas, but qualified catalyst faces huge challenges. Most catalysts reported for this reaction are deactivated fast by carbon deposition. Herein, we demonstrated an active, selective and stable molten tungsten-indium bimetal catalyst entrapped in a silica gel, offering 11% methane conversion in single pass, with C2/C3-C5/aromatics hydrocarbon distributions of 36%/4%/54% at 950 °C. A little carbon was formed during reaction, but spontaneously floated onto tungsten-indium liquid surface and moved onto silica surface thereby leaving the tungsten-indium liquid surface clean. No deactivation was thus observed even after 120-hour testing. Theoretical calculations and experimental results reveal that methane is converted into ethane on indium clusters, followed by gas-phase thermal cracking to ethylene and tandem aromatization on tungsten clusters to aromatics. The high stability and controllable hydrocarbon distribution promise our catalyst great potential of practical applications.

NH3-Selective Catalytic Reduction of NOx to N2 over Ceria Supported WOx Based Catalysts: Influence of Tungsten Content

A series of HPW/CeO2 catalysts generated from 12-tungstophosphoric acid, H3PW12O40 (HPW), supported on ceria and presenting different tungsten loadings (2, 4.5, 9, 16, and 40 wt% W) were prepared and characterized by N2 physisorption, XRD, IR, Raman, and UV-Vis. The different characterization techniques suggested that low loading of tungsten resulted in mainly isolated sites, while high tungsten loading produced polymeric or tungsten clusters. Those materials exhibited high activity in NH3-SCR of NOx into N2. Moreover, the series of experiments indicated that low loading in tungsten (2% HPW/CeO2) displayed the highest activity with a remarkable N2 selectivity (99%) at medium-high temperature (300–515 °C), owing to the high amount of monomeric tungstate coverage on the catalyst surface.

Aqueous biphasic system in differential extraction of arseno and phospho molybdenum blue: Consequent sensing of glutathione in acid-free medium

Polyoxometalates (POMs) are the oxyanion clusters of early transition metals (mostly molybdenum (VI), tungsten (VI) and vanadium (V)) and they show interesting properties particularly in the field of catalysis and sensing chemistry. In this work molybdenum blue (MB), phosphomolybdenum blue (PMB) and arsenomolybdenum blue (AsMB) are prepared using glutathione (GSH) as reducing agent in acid–free condition. The MB species are further characterised by UV–vis spectroscopy, Raman spectroscopy, XPS, powder XRD and FTIR spectroscopy. The prepared MB solutions showed an exciting behaviour in Aqueous Biphasic Systems (ABS) using PEG#4000 and Na2SO4 as phase forming components. MB and PMB partition to the micellar medium of PEG upto 44 % and 66 % respectively but AsMB is not at all partitioned. Therefore the method is useful for differentiating PMB and AsMB. PEG has been recovered using ultra-filtration technique after the ABS. The experiment also reveals that GSH, a biomolecule with high physiological impact, can be detected at trace concentrations by PMB formation method both in water and blood serum media.

Density functional theory study on the reducing agents for atomic layer deposition of tungsten using tungsten chloride precursor

We studied co-reactants for tungsten chloride precursors by density functional theory calculation to find the proper reducing agent. Tungsten chlorides, WCl6 and WCl5, are gaining attention for the fluorine-free atomic layer deposition (ALD) of tungsten. We created a W4Cl12 cluster by optimizing the number of tungsten and chlorine atoms in the chlorine-passivated tungsten cluster. We predicted the growth of tungsten carbide by the reaction of trimethylaluminum with the cluster, confirming that the cluster can mimic the chlorine-passivated tungsten surface. Then we simulated the reaction between the W4Cl12 cluster and four co-reactants. Possible reaction pathways between the cluster and the co-reactants were simulated to compare the reaction energies and activation energies. All co-reactants of the present work, atomic hydrogen, H2, SiH4, and B2H6, would act as reducing agents with the reaction energies of −2.07 eV, −0.01 eV, −0.28 eV, and −0.45 eV, respectively. The reducing power was in the order of atomic hydrogen, B2H6, SiH4, and H2 with activation energies of +0.04 eV, +0.18 eV, +1.18 eV, and +2.32 eV, respectively. B2H6 is the most promising gas-phase candidate due to its low activation energy for reduction and high activation energy for boron incorporation.

Neutral Chalcogenide Tungsten Cluster with Tris(2‐Cyanoethyl)phosphine

Despite the great prospects for the use of octahedral metal cluster complexes in various fields, chalcogenide tungsten compounds with functional organic ligands have practically not been studied. In this work, we present the synthesis and detailed characterization of a tungsten cluster with tris(2‐cyanoethyl)phosphine [{W6S8}(P(C2H4CN)3)6]. The compound has been obtained directly from (Bu4N)2[{W6Cl8}Cl6] in one step with a good yield. The crystal structure, determined by single‐crystal X‐ray diffraction analysis, as well as multinuclear NMR analysis have well confirmed the formation of the chalcogenide neutral cluster. Moreover, the electrochemical properties of the complex have been studied.

Activation of Methane by Tungsten Carbide and Nitride Cluster Cations.

Gas-phase reactions of tungsten carbide and nitride cluster cations, WnCm+ (n = 1-5, m ≤ 5) and WnNm+ (n = 1-6, m ≤ 2), with methane are investigated at near thermal energies. Most of the clusters react readily with CH4 to form WnCm+1H2+ or WnNmCH2+ under single collision conditions, in contrast to the almost no reactivity of pure tungsten clusters. This result indicates that the introduction of carbon or nitrogen atoms can enhance the reactivity of tungsten clusters toward the CH4 dehydrogenation. In addition, the formation and the release of an ethylene molecule are strongly suggested in the reaction of WC+ with CH4 as a minor reaction channel. Nearly all the nitride cluster cations, WnNm+ (n ≥ 2), exhibit higher reactivity than their corresponding carbides, WnCm+, whereas WN+ is less reactive than WC+. Furthermore, the multiple collision reactions of the highly reactive tungsten nitride species such as WN+ and W4N+ lead to the formation of WnNmCxH2x+ (x = 2, 3), which shows that the dehydrogenation of more than one CH4 molecule occurs.

Interaction of Hydrophobic Tungsten Cluster Complexes with a Phospholipid Bilayer.

Nanoconstructions composed of lipid vesicles and inorganic units (nanoparticles, metal complexes) arouse much interest across materials science and nanotechnology as hybrid materials combining useful functionalities from both parts. Ideally, these units are to be embedded into the bilayer to keep the biophysical performance of lipid vesicles having inorganic moieties screened from the environment. This can be achieved by doping a lipid bilayer with cluster complexes of transition metals. In this work, we report the preparation of nanoparticles from trinuclear W3S4 cluster complexes and egg phosphatidylcholine. A systematic study of their properties was performed by the differential scanning calorimetry, NMR spectroscopy, dynamic light scattering, and transmission electron microscopy. Phospholipids and clusters have been found to spontaneously self-assemble into novel cluster-lipid hybrid materials. The behavior of clusters in the hydrophobic lipid environment is determined by the structure of the ligands and cluster-to-lipid ratio. Intact cluster complexes bearing compact hydrophobic ligands are embedded into the hydrophobic midplane of a lipid bilayer, whereas cluster complexes bearing larger ligands drive the aggregation of lipids and cluster complexes. Considering these differences, it could be possible to obtain different self-assembled associates such as cluster-doped liposomes or lipid-covered crystals. These cluster-lipid hybrids can be a platform for the design of new materials for nanotechnology.