Synthesis and Structure of Hexatungstochromate(III), [H3CrIIIW6O24]6–

The hexatungstochromate(III) [H3CrIIIW6O24]6- (1) was synthesized in aqueous, basic medium by simple reaction of chromium(III) nitrate nonahydrate and sodium tungstate dihydrate in a 1:6 ratio. Polyanion 1 represents the first Anderson-Evans type heteropolytungstate with a trivalent hetero element. The sodium salt of 1 with the formula Na6[H3CrIIIW6O24]·22H2O (1a) was fully characterized in the solid state by single crystal XRD, FT-IR spectroscopy, and thermogravimetric analysis

MOLYBDENUM VERSUS TUNGSTEN BASED POLYOXOMETALATES FOR HIGHLY EFFECTIVE METHYLENE BLUE REMOVAL

[SiW12O40]4-(SiW12) and [Mo8O26]4- (Mo8) were synthesized and characterized by Fourier Transform Infrared spectroscopy (FTIR). The prepared polyoxometalates were studied as potential adsorbents for the removal of methylene blue (MB) from an aqueous solution. Various operational parameters—contact time, adsorbent dose, initial dye concentration, pH, and temperature— were meticulously assessed by UV/Vis spectrophotometry to study its impact on the adsorption efficacy. An inverse relationship was observed between the percentage dye removal and the initial dye concentration, highlighting the complexes\u27 superior adsorption capabilities under lower dye loads. The studied complexes displayed significantly better efficiency under acidic conditions. Both SiW12 and Mo8 exhibited high percentages of removal for methylene blue within only 10 min for MO8 and 5 min for SiW12. These results not only underline the proficiency of SiW12 and Mo8 as adsorbents, but also position them as promising candidates for fast and effective water purification strategies in the face of escalating environmental pollution challenges

Vanadium-based polyoxometalate as new material for sodium-ion battery anodes

Affordable energy storage is crucial for a variety of technologies. One option is sodium-ion batteries (NIBs) for which, however, suitable anode materials are still a problem. We report on the application of a promising new class of materials, polyoxometalates (POMs), as an anode in NIBs. Specifically, Na6[V10O28]·16H2O is being synthesized and characterized. Galvanostatic tests reveal a reversible capacity of approximately 276 mA h g−1 with an average discharge potential of 0.4 V vs. Na/Na+, as well as a high cycling stability. The underlying mechanism is rationalized to be an insertion of Na+ in between the [V10O28]6− anions rather than an intercalation into a crystal structure; the accompanying reduction of V+V to V+IV is confirmed by X-ray Photoelectron Spectroscopy. Finally, a working full-cell set-up is presented with the POM as the anode, substantiating the claim that Na6[V10O28]·16H2O is a promising option for future high-performing sodium-ion batteries

INNOVATIVE APPROACHES FOR THE PHOTOCATALYTICDEGRADATION OF PESTICIDES

Mono- and tri-vanadium-substituted Keggin-type heteropolyoxoanions [SiW12O40]4- and[PW12O40] 4- were evaluated as photocatalysts for the photodegradation of three hazardous food pesticides: Atrazine, Chlorpyrifos and Dieldrin. Kinetic experiments were performed under UV irradiation at 254nm. The degradation of each pesticide was assessed by investigating its disappearance with time using High Performance Liquid Chromatography c o n n e c t e d to an Ultra-Violet s p e c t r o p h o t ome t e r d e t e c t o r (HPLC-UV). The photocatalytic degradation of the three pesticides exhibited first order kinetics. It was found that the introduction of vanadium addenda atoms into the Keggin-type polyoxometalates decrease the degradation rate for the photocatalytic transformation of each pesticide as well as the degradation percentage. This effect was significantly related to the number of vanadium metal ions substituting the tungsten addenda atoms. As a general trend, the photocatalytic efficiency of {XVW11} was better than that of {XV3W9}. A marked drop was noticed in the photocatalytic degradation of Atrazine. 90% of Atrazine was decomposed in the presence of [a-SiW12O40] 4- at a rate of 1 ppm/min whereas the degradation percentage decreased to 5 5 % i n t h e presence of [a-SiVW11O40] 5- at a decreased rate of 0.7 ppm/min

Photocatalytic degradation of atrazine by heteropolyoxotungstates

An elegant and eco-friendly photocatalytic degradation approach for the most commonly used herbicide, Atrazine (ATZ); allowed a selective and partial degradation into atrazine-2-hydroxy (Hydroxyatrazine, HAT), which was the sole obtained metabolite. The effect of tungstosilicates and tungstophosphates as photocatalysts under 60 min UV irradiation at two different wavelengths; 254 and 366 nm; was investigated by measuring the absorbance at 10-min intervals, using 720-UV spectrophotometry. ATZ conversion rate was the highest when irradiating with the higher-energy 254 nm UV light. This resulted into 54% degradation in the presence of the silicon-based α-Keggin dodecatungstosilicate [α-SiW12O40]4−, whereas 17% was decomposed in its absence. The nature of the heteroatom as well as the structural type of the studied polyoxometalates had a significant effect on the degradation percentage. Accordingly, 31% of ATZ was only decomposed in presence of the phosphorus-analogue [α-PW12O40]4− whereas the cyclic super-lacunary octatetracontatungstooctaphosphate [P8W48O184]40− increased the degradation to 41%

Cytotoxicity and enzyme inhibition studies of polyoxometalates and their chitosan nanoassemblies

Polyoxometalates (POMs) have become very significant in biomedical research for their structural diversity which renders them highly active against bacterial, viral and cancer diseases. In this study three different POMs were synthesized and nanoassemblies were made with chitosan (CTS), a natural biodegradable polymer with excellent drug carrier properties. The compounds were tested on two isoenzymes of alkaline phosphatases including tissue specific calf intestine alkaline phosphatase (CIAP) and tissue non-specific alkaline phosphatase (TNAP). Compound [TeW6O24]6− (TeW6) showed the highest activity (45.4 ± 11.3 nM) among tested compounds against TNAP. Similarly, chitosan-[TeW6O24]6− (CTS-TeW6) was proved to be a potent inhibitor of CIAP with Ki value of 22 ± 7 nM. A comparative study was made to evaluate their cytotoxic potential against HeLa cells. Among all tested compounds, Chitosan-[NaP5W30O110]14− (CTS-P5W30) has showed higher percent cytotoxicity (88 ± 10%) at 10 μM when compared with the standard anticancer drug vincristine (72 ± 7%). The study revealed that selected POMs proved excellent anticancer potential and were equally effective against alkaline phosphatase enzyme, an increased level of which may indicate cancer metastasis

Synthesis, Detailed Characterization, and Theoretical Understanding of Mononuclear Chromium(III)-Containing Polyoxotungstates [Cr^III(HX^VW₇O₂₈)₂]^13– (X = P, As) with Exceptionally Large Magnetic Anisotropy

Two monochromium­(III)-containing heteropolytungstates, [Cr^III(HP^V­W₇O₂₈)₂]^13‑ (<b>1a</b>) and [Cr^III(HAs^V­W₇O₂₈)₂]^13‑ (<b>2a</b>), were prepared via simple, one-pot reactions in aqueous, basic medium, by reaction of the composing elements, and then isolated as hydrated sodium salts, Na₁₃[Cr^III(HP^V­W₇O₂₈)₂]·47H₂O (<b>1</b>) and Na₁₃[Cr^III(HAs^V­W₇O₂₈)₂]·52H₂O (<b>2</b>). Polyanions <b>1a</b> and <b>2a</b> comprise an octahedrally coordinated Cr^III ion, sandwiched by two {PW₇} or {AsW₇} units. Both compounds <b>1</b> and <b>2</b> were fully characterized in the solid state by single-crystal XRD, IR spectroscopy, thermogravimetric and elemental analyses, magnetic susceptibility, and EPR measurements. Magnetic studies on <b>1</b> and <b>2</b> demonstrated that both compounds exhibit appreciable deviation from typical paramagnetic behavior, and have a ground state S = ³/₂, as expected for a Cr^III ion, but with an exceptionally large zero-field uniaxial anisotropy parameter (<i>D</i>). EPR measurements on powder and single-crystal samples of <b>1</b> and <b>2</b> using 9.5, 34.5, and 239.2 GHz frequencies and over 4–295 K temperature fully support the magnetization results and show that <i>D</i> = +2.4 cm^–1, the largest and sign-assigned <i>D</i>-value so far reported for an octahedral Cr^III-containing, molecular compound. Ligand field analysis of results from CASSCF and NEVPT2-correlated electronic structure calculations on Cr­(OH)₆^3– model complexes allowed to unravel the crucial role of the second coordination sphere of Cr^III for the unusually large magnetic anisotropy reflected by the experimental value of <i>D</i>. The newly developed theoretical modeling, combined with the synthetic procedure for producing such unusual magnetic molecules in a well-defined and essentially magnetically isolated environment, appears to be a versatile new research area

Synthesis, Detailed Characterization, and Theoretical Understanding of Mononuclear Chromium(III)-Containing Polyoxotungstates [Cr^III(HX^VW₇O₂₈)₂]^13– (X = P, As) with Exceptionally Large Magnetic Anisotropy

Two monochromium­(III)-containing heteropolytungstates, [Cr^III(HP^V­W₇O₂₈)₂]^13‑ (<b>1a</b>) and [Cr^III(HAs^V­W₇O₂₈)₂]^13‑ (<b>2a</b>), were prepared via simple, one-pot reactions in aqueous, basic medium, by reaction of the composing elements, and then isolated as hydrated sodium salts, Na₁₃[Cr^III(HP^V­W₇O₂₈)₂]·47H₂O (<b>1</b>) and Na₁₃[Cr^III(HAs^V­W₇O₂₈)₂]·52H₂O (<b>2</b>). Polyanions <b>1a</b> and <b>2a</b> comprise an octahedrally coordinated Cr^III ion, sandwiched by two {PW₇} or {AsW₇} units. Both compounds <b>1</b> and <b>2</b> were fully characterized in the solid state by single-crystal XRD, IR spectroscopy, thermogravimetric and elemental analyses, magnetic susceptibility, and EPR measurements. Magnetic studies on <b>1</b> and <b>2</b> demonstrated that both compounds exhibit appreciable deviation from typical paramagnetic behavior, and have a ground state S = ³/₂, as expected for a Cr^III ion, but with an exceptionally large zero-field uniaxial anisotropy parameter (<i>D</i>). EPR measurements on powder and single-crystal samples of <b>1</b> and <b>2</b> using 9.5, 34.5, and 239.2 GHz frequencies and over 4–295 K temperature fully support the magnetization results and show that <i>D</i> = +2.4 cm^–1, the largest and sign-assigned <i>D</i>-value so far reported for an octahedral Cr^III-containing, molecular compound. Ligand field analysis of results from CASSCF and NEVPT2-correlated electronic structure calculations on Cr­(OH)₆^3– model complexes allowed to unravel the crucial role of the second coordination sphere of Cr^III for the unusually large magnetic anisotropy reflected by the experimental value of <i>D</i>. The newly developed theoretical modeling, combined with the synthetic procedure for producing such unusual magnetic molecules in a well-defined and essentially magnetically isolated environment, appears to be a versatile new research area