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

Photo-assisted water oxidation by high-nuclearity cobalt-oxo cores: tracing the catalyst fate during oxygen evolution turnover

Multi-nuclear cobalt cores have been proposed as molecular analogues of the natural oxygen evolving complex, enabling water oxidation for artificial photosynthesis schemes and the production of solar fuels. In particular, cobalt containing polyoxometalates (Co-POMs) display a record activity as water oxidation catalysts (WOCs) in terms of the turnover number, turnover frequency, and quantum yield, when combined in a light activated oxygen evolving cycle with Ru(bpy)32+ (bpy = 2,2’-bipyridine) as the photosensitizer. The unique behavior of high-nuclearity cobalt clusters is addressed herein by employing Co-POMs with Co ≥9 as molecular WOCs. The temporal dissection of the catalytic events is framed herein to investigate the initial photo-induced electron transfer (ET) occurring in the micro-to-millisecond time domain, and followed by the oxygen evolution kinetics taking place within a minute-to-hours regime. In particular, flash photolysis shows ET from the Co-POM to photogenerated Ru(bpy)33+ with well-behaved diffusional kinetics (bimolecular rate constants in the range kET = 2.1–5.0 × 109 M−1 s−1) and counting up to 32 ET events in a 60 ms timeframe. The evolution of the Co-POMs is then traced under oxygenic conditions, where infrared and X-ray absorption spectroscopy (XAS) indicate that POM based structures are competent catalysts under the photo-assisted turnover regime

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

Cr^III-Substituted Heteropoly-16-Tungstates [Cr^III₂(<i>B</i>‑β‑X^IVW₈O₃₁)₂]^14– (X = Si, Ge): Magnetic, Biological, and Electrochemical Studies

The dichromium­(III)-containing heteropoly-16-tungstates [Cr^III₂(<i>B</i>-β-Si^IVW₈O₃₁)₂]^14– (<b>1</b>) and [Cr^III₂(<i>B</i>-β-Ge^IVW₈O₃₁)₂]^14– (<b>2</b>) were prepared via a one-pot reaction of the composing elements in aqueous, basic medium. Polyanions <b>1</b> and <b>2</b> represent the first examples of Cr^III-containing heteropolytungstates comprising the octatungstate unit {XW₈O₃₁} (X = Si, Ge). Magnetic studies demonstrated that, in the solid state, the two polyanions exhibit a weak antiferromagnetic interaction between the two Cr^III centers with <i>J</i> = −3.5 ± 0.5 cm⁻¹, with no long-range ordering down to 1.8 K. The ground-state spin of polyanions <b>1</b> and <b>2</b> was thus deduced to be 0, but the detection of a complex set of EPR signals implies that there are thermally accessible excited states containing unpaired spins resulting from the two <i>S</i> = ³/₂ Cr^III ions. A comprehensive electrochemistry study on <b>1</b> and <b>2</b> in solution was performed, and biological tests showed that both polyanions display significant antidiabetic and anticancer activities