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We report on the synthesis and structural characterization of two series of lanthanide-containing 22-tungsto-2-germanates. The first series corresponds to a family of polyanions with the formula [Ln(

We have synthesized and structurally characterized three tetra-(

Background: Polyoxometalates (POMs) are negatively charged metal-oxo clusters of early transition metal ions in high oxidation states (e.g., WVI, MoVI, VV). POMs are of interest in the fields of catalysis, electronics, magnetic materials and nanotechnology. Moreover, POMs were shown to exhibit biological activities in vitro and in vivo, such as antitumor, antimicrobial, and antidiabetic. Methods: The literature search for this peer-reviewed article was performed using PubMed and Scopus databases with the help of appropriate keywords. Results: This review gives a comprehensive overview of recent studies regarding biological activities of polyoxometalates, and their biomedical applications as promising anti-viral, anti-bacterial, anti-tumor, and anti-diabetic agents. Additionally, their putative mechanisms of action and molecular targets are particularly considered. Conclusion: Although a wide range of biological activities of Polyoxometalates (POMs) has been reported, they are to the best of our knowledge not close to a clinical trial or a final application in the treatment of diabetes or infectious and malignant diseases. Accordingly, further studies should be directed towards determining the mechanism of POM biological actions, which would enable fine-tuning at the molecular level, and consequently efficient action towards biological targets and as low toxicity as possible. Furthermore, biomedical studies should be performed on solutionstable POMs employing physiological conditions and concentrations.

In this study, the in vivo hypoglycemic effect of a donut-shaped polyanion salt (NH4)14[Na@P5W30O110]·31H2O {NaP5W30} and its Ag-containing derivative K14[Ag@P5W30O110]·22H2O·6KCl {AgP5W30}, as well as their hepatotoxicity and nephrotoxicity, was evaluated. In the screening hypoglycemic study, Wistar albino rats with streptozotocin induced diabetes were treated intraperitoneally with three single doses (5, 10, and 20 mg per kg per b.w.) of both investigated polyoxotungstates. The blood glucose levels, measured before and after 2, 4 and 6 h polyoxotungstate application, showed that both studied compounds induced the most pronounced and time dependent glucose lowering effects at the doses of 20 mg kg−1. Thus, daily doses of 20 mg kg−1 were administered to Wistar albino rats orally for 14 days in further toxicity examinations. The serum glucose concentration and biochemical parameters of kidney and liver function, as well as a histopathological analysis of kidney and liver tissues were evaluated 14 days after the polyoxotungstate administration. Both investigated compounds did not induce statistically significant alterations of the serum glucose and uric acid concentrations, as well as some of the liver function markers (serum alanine and aspartate aminotransferases, and alkaline phosphatase activities). However, the significant decrease in serum total protein and albumin concentrations and the increase in biochemical parameters of renal function – serum urea (up to 63.1%) and creatinine concentrations (up to 23.3%) were observed for both polyoxotungstates. In addition, the detected biochemical changes were in accordance with kidney and liver histhopathological analysis. Accordingly, the hepatotoxic and nephrotoxic effects of these potential antidiabetic polyoxotungstates could be considered as mild.

Interaction of the mixed-valent 12-manganese coordination complex [MnIII 8MnIV 4O12(CH3COO)16(H2O)4] with the lacunary 9-tungstoarsenate(V) [A-α-AsW9O34]9− resulted in the 10-manganese(III/IV)-containing 36-tungsto-4-arsenate(V), [MnIII 6MnIV 4O4(OH)12(H2O)12(A-β-AsW9O34)4]22− (1). Polyanion 1 was isolated as a hydrated mixed potassium–sodium salt, K14Na8[MnIII 6MnIV 4O4(OH)12(H2O)12(A-β-AsW9O34)4]·104H2O, which crystallizes in the orthorhombic space group Pbcn and was characterized by FT–IR spectroscopy and single-crystal X-ray diffraction, as well as elemental and thermogravimetric analyses. The title polyanion contains a unique [MnIII 6MnIV 4O4(OH)12(H2O)12]14+ core stabilized within the 36-tungsto-4-arsenate(V) framework.

The palladium(II)-containing 40-tungsto-4-arsenate(III) [Pd2Na2KAs4W40O140(H2O)](21-) (1a) was synthesized by reaction of PdSO4 with the cryptate heteropolyanion [As4W40O140](28-) in potassium acetate buffer. The title compound was characterized by single-crystal XRD, IR, TGA, and elemental analysis.

ConspectusNoble metal catalysts, in particular palladium-containing materials, are of prime commercial interest, because of their role as oxidation catalysts in automobile emission-control systems and reforming catalysts for the production of high-octane gasoline. However, despite almost two centuries of research, the precise structure of such materials is still ill-defined on the sub-nanometer scale, which severely limits the understanding of the underlying catalytic mechanisms. As a burgeoning class of structurally well-defined noble metal oxide nanoclusters, polyoxopalladates (POPs) have been highly rated as ideal models to fully decipher the molecular mechanism of noble metal-based catalysis. Being at the frontier of polyoxometalates (POMs), the chemistry of POPs, which are based exclusively on PdII centers as addenda is currently progressing rapidly, owing to their structural and compositional novelty, high solution stability, combined with promising applications especially as noble metal-based catal...

Here we report on the synthesis and structural characterization of the dithallium(III)-containing 30-tungsto -4-phosphate [Tl2Na2(H2O)2{P2W15O56}2]16- (1) by a multitude of solid-state and solution techniques. Polyanion 1 comprises two octahedrally coordinated Tl3+ ions sandwiched between two trilacunary {P2W15} Wells-Dawson fragments and represents only the second structurally characterized, discrete thallium-containing polyoxometalate to date. The two outer positions of the central rhombus are occupied by sodium ions. The title polyanion is solution-stable as shown by 31P and 203/205Tl NMR. This was also supported by Tl NMR spectra simulations including several spin systems of isotopologues with half-spin nuclei (203Tl, 205Tl, 31P, 183W). 23Na NMR showed a time-averaged signal of the Na+ counter cations and the structurally bonded Na+ ions. 203/205Tl NMR spectra also showed a minor signal tentatively attributed to the trithallium-containing derivative [Tl3Na(H2O)2(P2W15O56)2]14-, which could also be identified in the solid state by single-crystal X-ray diffraction. The bioactivity of polyanion 1 was also tested against bacteria and Leishmania.

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Three types of macroanion-countercation interactions in dilute solution, decided by the strength of electrostatic attraction and the change of hydration shells are reported: minor interaction between macroanions [MO8 Pd12 (SeO3 )8 ]6- (M=Zn2+ or Ni2+ ) and monovalent cations (Na+ , K+ , Rb+ , Cs+ ), leaving their hydration shells intact (solvent-separated ion-pairs); strong binding between macroanions and divalent cations (Sr2+ , Ba2+ ) to form solvent-shared ion-pairs with partial dehydration; very strong electrostatic attraction between macroanions and Y3+ ion with contact ion-pairs formation by severely breaking their original hydration shells and forming new ones. In addition, divalent cations can help the macroanions self-assemble into hollow spherical blackberry structures through counterion-mediated attraction, whereas macroanions with mono- or trivalent cations only stay as discrete ions due to either weak interaction or a small number of bound countercations.

The 15-copper(ii)-containing 36-tungsto-4-silicates [Cu15O2(OH)10X(A-α-SiW9O34)4]25- (X = Cl, 1; Br, 2) have been prepared in 70% yield by reaction of the trilacunary 9-tungstosilicate precursor [A-α-SiW9O34]10- with Cu2+ ions in aqueous pH 8 medium. Both polyanions 1 and 2 were isolated as hydrated mixed potassium/sodium salts and characterized in the solid state by FT-IR, TGA, single-crystal XRD, and elemental analysis. DC magnetic susceptibility measurements from 1.8-300 K established the ground state to be paramagnetic with a magnetic moment corresponding to 15 uncoupled Cu2+ (S = 1/2) ions. EPR measurements and simulations were consistent with this analysis. Electrochemical studies were performed for polyanions 1 and 2 dissolved in solution to elucidate the electroactivity of both copper and tungstate sites. Using 2 as a representative example, the electrocatalytic activity towards CO2 reduction upon deposition on a glassy carbon electrode surface, while retaining selectivity relative to hydrogen evolution, was demonstrated.

In the current study, electrostatically-driven pH responsive, supramolecular hydrogels of the trilacunary Wells-Dawson-type 15-tungsto-2-phosphate polyanion (P2W15) and chitosan hydrochloride (ChCl) were prepared, using methacrylic acid as pH responsive agent using benzoyl peroxide (BPO) as initiator. The prepared hydrogels were characterized by FT-IR, SEM, XRD and thermal analyses (TGA-DSC). The swelling and pH based P2W15 release profile of the hydrogels showed maximum swellability and release at pH 7.4. Different mathematical models were applied, showing that P2W15 release followed supercase transport-II mechanism and zero-order kinetics. The cytotoxicity results showed that free and embedded P2W15 exhibited dose-dependent cytotoxicity against cancer cell lines (MCF-7; HeLa) with minimal effects on normal cells (Vero). The developed hydrogels were administered to the rabbits for determining the pharmacokinetic behavior of the polyanion. Moreover, the developed hydrogel system as well as polyanion concentration used were also checked for its oral tolerability and safety evaluation in rabbits. The histopathological studies, serum chemistry (except blood glucose level) and hematological investigations exhibited that administered hydrogel suspension at maximal tolerable dose (4000mg/kg body weight) and polyanion concentration used (20mg) were safe from in-vivo point of view. The developed hydrogels exhibited desirable qualities of a drug delivery system that can be used for the delivery of the embedded polyanion.

A toxicity evaluation of two Keggin-type heteropolytungstates, K-7[Ti2PW10O40].6H(2)O and K6H [SiV3W9O40].3H(2)O, with different inhibitory potencies toward acetylcholinesterase activity (IC50 values of 1.04 x 10(-6) and 4.80 x 10(-4) mol/L, respectively) was performed. Wistar albino rats were orally treated with single doses (5 and 50 mg/kg) of both investigated compounds. The biochemical parameters of renal (serum urea and creatinine) and liver function (direct and total bilirubin, alanine transaminase, and aspartate aminotransferase) were determined after 24 h and 14 days. A histopathological analysis of liver tissue was carried out 14 days after the polyoxotungstate administration. Both applied doses of the investigated compounds did not induce statistically significant alterations of the renal function markers. However, the polyoxotungstate treatment caused an increase in the activities of serum alanine transaminase and aspartate aminotransferase in a time- and concentration -dependent manner, although statistically significant changes in bilirubin concentrations were not observed. Furthermore, the detected hepatotoxic effect was confirmed by histhopathological analysis that suggested some reversible liver tissue damage two weeks after the treatment, especially in the case of K6H [SiV3W9O40]-3H(2)O. Accordingly, the toxicity of these two polyoxotungstates with anti-acetylcholinesterase effect cannot be considered as a severe one, but their potential clinical application would require a more complex toxicological study.

In the present study electrostatically-driven pH responsive supramolecular, self-assembled hydrogels of the trilacunary Wells-Dawson-type 15-tungsto-2-phosphate polyanion [P2W15O56]12− (P2W15) and polyethyleneimine were prepared. Crosslinking was achieved through electrostatic interactions between cationic polyethyleneimine and P2W15. The pH responsiveness was induced by acrylic acid. Benzoyl peroxide was used as an initiator, for initiating the polymerization reaction, anchoring polyacrylic acid on the polyethyleneimine skeleton. The prepared sea-green color hydrogels were characterized by FT-IR, SEM, XRD and thermal analysis (TGA-DSC). The swelling index, P2W15 release studies and pH responsive properties of the developed supramolecular hydrogels were evaluated at pH 1.2 and 7.4, showing maximum swellability and release characteristics at pH 7.4. For determining the P2W15 release mechanism different mathematical models such as zero order, first order, Higuchi model and Krosmeyer-Peppas models were applied and the results showed that embedded P2W15 release follows zero-order kinetics. The cytotoxicity results showed that naked and embedded P2W15 exhibited dose-dependent cytotoxicity against cancer cell lines (MCF-7; Hela) with minimal effects on normal cells (Vero). The hydrogels developed through electrostatic interactions exhibited desirable qualities of a drug delivery system that can be used for the delivery of the embedded polyanion.

Polyoxometalates (POMs) have been reported as promising electrode materials for energy storage applications due to their ability to undergo fast redox reactions with multiple transferred electrons per polyanion. Here we employ a polyoxovanadate salt, Na6[V10O28], as an electrode material in a lithium-ion containing electrolyte and investigate the electron transfer properties of Na6[V10O28] on long and short timescales. Looking at equilibrated systems, in situ V K-edge X-ray absorption near edge structure (XANES) studies show that all 10 V5+ ions in Na6[V10O28] can be reversibly reduced to V4+ in a potential range of 4–1.75 V vs. Li/Li+. Focusing on the dynamic response of the electrode to potential pulses, the kinetics of Na6[V10O28] electrodes and the dependence of the fundamental electron transfer rate k0 on temperature are investigated. From these measurements we calculate the reorganization energy and compare it with theoretical predictions. The experimentally determined reorganization energy of λ = 184 meV is in line with the theoretical estimate and confirms the hypothesis of small values of λ for POMs due to electrostatic shielding of the redox center from the solvent.

We have prepared the indium(III)-centered, all-acetate-capped polyoxopalladate(II) nanocube [InPd

The first two examples of polyoxopalladates(II) (POPs) containing tetravalent metal ion guests, [MO

The class of peroxo-cerium-containing polyoxometalates has been discovered via the synthesis of the 9-peroxo-6-cerium(IV)-containing 30-tungsto-3-germanate, [Ce

Despite their attractive properties, internal targeted alpha therapies using 223/224Ra are limited to bone-seeking applications. As there is no suitable chelator available, the search for new carriers to stably bind Ra2+ and to connect it to biological target molecules is necessary. Polyoxopalladates represent a class of compounds where Ra2+ can be easily introduced into the Pd-POM core during a facile one-pot preparation. Due to the formation of a protein corona, the connection to other targeting (bio)macromolecules is possible.

We report on a fast microwave-assisted synthetic procedure of the Wells-Dawson-type 18-tungsto-2-phosphate [P2W18O62]6− with a 35% yield in 24 h, rather than a week using conventional heating.

The four 18-tungsto-2-arsenates(III) [MII(H2O)(TiIVO)2(α-AsIIIW9O33)2]12– [M = Co (CoTi2), Ni (NiTi2), Cu (CuTi2), Zn (ZnTi2)] were rationally synthesized by treating the respective divalent metal ions with the monolacunary, dititanium(IV)-containing polyanion precursor [(TiIVO)2(α-AsIIIW9O33)2]14– (Ti2) in aqueous solution. All four polyanions are isostructural and correspond to dimers with two Ti4+ and one M2+ ion sandwiched between two [α-AsIIIW9O33]9– units. The compounds were characterized in the solid state by single-crystal XRD, infrared spectroscopy, thermogravimetric analysis, and elemental analysis and in solution by UV/Vis and NMR spectroscopy as well as electrochemistry. Variable-temperature magnetic susceptibility and variable-field magnetization characterization of the paramagnetic derivatives indicate antiferromagnetic interactions between nearest neighbors in the solid state. The resolved hyperfine structure obtained from multifrequency EPR measurements on CuTi2 (which exhibits a Jahn–Teller effect) in the solid state lead us to assign the ground state mainly to the Cu dx²–y² orbital. Despite the fact that the four polyanions are isostructural and have the same overall negative charge, the cyclic voltammetric patterns featuring their chemically reversible reduction waves display distinct features. Electrocatalytic studies demonstrate that the activities of the polyanions towards nitrate reduction are strikingly influenced by the nature of the substituent metal ion.

We introduce the class of discrete silver(I)-palladium(II)-oxo nanoclusters with the preparation of {Ag4Pd13} and {Ag5Pd15}. Both polyanions represent the first examples of noble metal-capped polyoxo-noble-metalates in a fully inorganic assembly, featuring an unprecedented host–guest mode containing hetero- and homometallic Ag–Pd and Ag–Ag bonding interactions. Comprehensive theoretical calculations suggest that the Ag–Pd metallic bonds originate partially from surface confinement of AgI guest ions onto the anionic polyoxopalladate host that is induced by strong electrostatic forces. This work opens the field of fully inorganic silver-palladium-oxo nanoclusters, which can be considered as discrete mixed noble metal precursors for the formation of monodisperse core–shell nanoparticles, with high relevance for catalysis.

Die beiden diskreten Silber(I)-Palladium(II)-Oxo-Nanocluster {Ag4Pd13} und {Ag5Pd15} sind die ersten Beispiele von edelmetallverkappten Polyoxoedelmetallaten mit einem neuartigen Wirt-Gast-Bindungsmodus, der hetero- und homometallische Ag-Pd- und Ag-Ag-Wechselwirkungen beinhaltet. Umfassende theoretische Studien deuten darauf hin, dass die Ag-Pd-Metallbindungen teilweise von einem Polyanion-Oberflacheneffekt auf die AgI-Gastionen herruhren, der durch starke elektrostatische Krafte induziert wird. Diese Arbeit eroffnet ein Gebiet komplett anorganischer Silber-Palladium-Oxo-Nanocluster, die als Vorstufen fur die Bildung monodisperser Kern-Schale-Nanopartikel angesehen werden konnen, welche eine hohe Relevanz im Bereich der Katalyse haben.

The cage-like cyclobutyltellurium(IV)-containing tungstoarsenate(III) dimers [(C4H8Te-OH)2(C4H8Te)6{As2W17O61(H2O)}2]14− (1) and [{(C4H8Te)2W2O5(H2O)2As2W19O67(H2O)}2]16− (2) were synthesized in moderately acidic aqueous medium by reaction of C4H8TeI2 with the lacunary tungstoarsenates(III) [B-α-AsW9O33]9− and [As2W19O67(H2O)]14−, respectively. Polyanion 1 was isolated as a mixed cesium-guanidinium salt Cs8.5(C(NH2)3)5.5[(C4H8TeOH)2(C4H8Te)6{As2W17O61(H2O)}2]·60H2O (1a), whereas 2 crystallized as a mixed cesium-potassium salt Cs9K7[{(C4H8Te)2W2O5(H2O)2As2W19O67(H2O)}2]·90H2O (2a). Single crystal X-ray analysis demonstrated that 1a and 2a crystallized in the triclinic space group $$ P \bar{1} $$ , with a = 12.7738(8) A, b = 18.7490(14) A, c = 21.9831(14) A, α = 111.155(4)o, β = 93.312(3)o, γ = 99.530(4) and Z = 1 for 1a and a = 19.309(6) A, b = 24.674(8) A, c = 26.071(8) A, α = 63.218(17)°, β = 89.26(16)°, γ = 79.948(17)° and Z = 2 for 2a. The polyanion salts 1a and 2a were characterized by solid state NMR (1H, 13C, 125Te), FT-IR, TGA-DSC, and elemental analysis.

The dichromium(III)-containing heteropoly-16-tungstates [CrIII2(B-β-SiIVW8O31)2]14- (1) and [CrIII2(B-β-GeIVW8O31)2]14- (2) were prepared via a one-pot reaction of the composing elements in aqueous, basic medium. Polyanions 1 and 2 represent the first examples of CrIII-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 CrIII centers with J = -3.5 ± 0.5 cm-1, with no long-range ordering down to 1.8 K. The ground-state spin of polyanions 1 and 2 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 S = 3/2 CrIII ions. A comprehensive electrochemistry study on 1 and 2 in solution was performed, and biological tests showed that both polyanions display significant antidiabetic and anticancer activities.

We have synthesized and structurally characterized the first discrete thallium-containing polyoxometalate, [Tl2{B-β-SiW8O30(OH)}2]12– (1). Polyanion 1 was characterized in the solid-state and shown to be solution-stable by 203/205Tl NMR, electrospray ionization mass spectrometry, and electrochemical studies. The antibacterial activity of 1 was also investigated.

(-)-Quinic acid possess eight possible stereoisomers, which occur both naturally and as products of thermal food processing. In this contribution, we have selectively synthesized four isomers, namely, epi-quinic acid, muco-quinic acid, cis-quinic acid, and scyllo-quinic acid, to develop a tandem LC-MS method identifying all stereoisomeric quinic acids. Four derivatives have been unambiguously characterized by single-crystal X-ray crystallography. The missing diastereomers of quinic acid were obtained by nonselective isomerization of (-)-quinic acid using acetic acid/concentrated H2SO4 allowing chromatographic separation and assignment of all diastereomers of quinic acid. We report for the first time that a full set of stereoisomers are reliably distinguishable on the basis of their tandem mass spectrometric fragment spectra as well as their elution order. A rationale for characteristic fragmentation mechanisms is proposed. In this study, we also observed that muco-quinic acid, scyllo-quinic acid, and epi-quinic acid are present in hydrolyzed Guatemalan roasted coffee sample as possible products of roasting.

The purpose of the study was to develop physically cross-linked novel pH-responsive gelatin – Wells–Dawson-type polyoxometalate (POM)-based self-assembled hydrogels using acrylic acid as a pH-responsive monomer. Cross-linking was achieved through electrostatic interactions between the cationic polymer and anionic Wells–Dawson POM [P2W15O56]12−. Ammonium persulfate and sodium hydrogen sulfite were used as initiators. The hydrogels were yellowish in color and exhibited low mechanical strength. Swelling, drug release, and pH sensitivity studies were conducted at pH 1.2 and 7.4. pH-dependent swelling and release of [P2W15O56]12− from the prepared hydrogels were observed, with a maximum at pH 7.4. The hydrogels were characterized by thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, and Fourier transform infrared spectroscopy for evaluation of the surface morphology, hydrogel confirmation, and thermal properties. The results obtained confirmed the development o...

The two 16-manganese-containing, Keggin-based 36-tungsto-4-silicates [Mn(III)10Mn(II)6O6(OH)6(PO4)4(A-α-SiW9O34)4](28-) (1) and [Mn(III)4Mn(II)12(OH)12(PO4)4(A-α-SiW9O34)4](28-) (2) have been prepared by reaction of the trilacunary Keggin precursor [A-α-SiW9O34](10-) with either Mn(OOCCH3)3·2H2O (for 1) or MnCl2·4H2O (for 2), in aqueous phosphate solution at pH 9. Polyanions 1 and 2 comprise mixed-valent, cationic {Mn(III)10Mn(II)6O6(OH)6}(24+) and {Mn(III)4Mn(II)12(OH)12}(24+) cores, respectively, encapsulated by four phosphate groups and four {SiW9} units in a tetrahedral fashion. Both polyanions were structurally and compositionally characterized by single-crystal XRD, IR, thermogravimetric analysis, and X-ray absorption spectroscopy. Furthermore, studies were performed probing the magnetic, electrochemical, oxidation catalytic, and Li-ion battery performance of 1 and 2.

A beneficial "microenvironment effect" on the efficiency of confined electrocatalysts is predicted by theory. However, examples of its experimental confirmation are scarce for catalysts based on polyoxometalates for the hydrogen evolution reaction (HER). For this purpose, the cyclic 48-tungsto-8-phosphate [H7P8W48O184](33) (P8W48) was fixed in a 3D configuration on reduced graphene oxide sheets (rGO) to boost its HER activity. The HRTEM imaging and the solid state P-31 NMR spectrum of P8W48/rGO reveal a strong interaction between individual P8W48 and transparent rGO sheets. The calculation of the interaction between P8W48 and graphene (G) sheets is difficult to perform within a reasonable period of time because of the large size and very high overall negative charge of P8W48. However, as P8W48 is symmetrical, a quarter of its structure [H2P2W12O48](12-) (P2W12) was extracted as a DFT calculation model. As P8W48 in P8W48/rGO is neutral, due to surrounding counter cations, the calculation model P2W12 is neutral with protons considering the affordable computational time. The adsorption energy for P2W12 on G (-1.55 eV) and the charge transfer between P2W12 and G (0.66 vertical bar e vertical bar) indicate that a strong interaction between P2W12 and G sheets exists. Kinetic studies show that the P8W48/rGO hybrids display excellent HER activity in acid, further confirmed by reproducible generation of hydrogen with quantitative faradaic yield and a high turnover frequency (11 s(-1) at 295 mV overpotential) for a noble metal-free electrocatalyst. Importantly, the overpotentials required for the HER compare well with those of the commercial Pt/C (20 wt% Pt), which indicates that P8W48/rGO is a promising cheap HER electrocatalyst. We demonstrate here the most convincing experimental evidence of the "microenvironment effect" on HER electrocatalysis by a polyoxometalate.

We report on the feasibility of applying high-resolution solid-state 195Pt MAS NMR spectroscopy for several PtIV-containing polyoxotungstates, and of 195Pt as well as 51V for a PtIV-containing polyoxovanadate. This method is particularly useful for polyanions which are unstable in solution and/or poorly soluble, as well as for systems exhibiting crystallographic disorder of Pt and W sites. We also report solution 195Pt and 183W NMR spectra of hexatungstoplatinate(IV) [H3PtW6O24]5− for the first time.

The polyoxo-22-palladate [Na2PdII22O12(AsVO4)15(AsVO3OH)]25− (1), which represents a novel polyoxo-noble-metalate structural type, was synthesized by reaction of Pd2+ and AsO43− ions in aqueous solution. Polyanion 1 comprises two {NaPd11} units linked by two arsenate bridges, and hence represents the first example of a defect, monolacunary {Pd11} polyoxopalladate nanocube with arsenate capping groups. The title polyanion was characterized in the solid state as well as by theoretical calculations.

Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for future electronics. Currently, the growth of TMD large area thin films/flakes is one of the biggest challenges. A novel method for the growth of ultra-thin and large area WS2 monolayer flakes has been developed by introducing a solution-based temperature-dependent process. This two-dimensional WS2 growth process is low cost and environmentally friendly. WO3 flakes are grown at the air–liquid interface using ammonium tetrathiotungstate ((NH4)2WS4, ATTW) as WS2 precursor. The process requires a moderate activation temperature as no flakes are formed at room temperature. Successful growth of flakes was observed in an aqueous solution of the precursor at a temperature between 70 °C and 90 °C. These flakes could be transferred to any substrate by a controlled dip-coating process. Large 2D WS2 flakes with a lateral size of up to 100 μm were obtained after sulfurization. The thickness ranged from a WS2 monolayer to five monolayers, as verified by atomic force microscope. The chemical reaction mechanism behind the formation of the flakes was investigated by FTIR, Raman, UV–Vis and x-ray photoelectron spectroscopy. The initial flakes were found to be made of WO3, which were successfully converted to WS2 by a post annealing step at 500 °C–900 °C. This simple and environmentally friendly growth technique can be used to produce large WS2 flakes for next generation electronics.

The investigation of conditions allowing multi-electron reduction and reoxidation of polyoxometalate (POM) films onto solid substrates is considered an issue of critical importance for their successful incorporation in electronic devices, different types of sensors and catalytic systems. In the present paper, the rich multi-electron redox chemistry of films of Wells–Dawson ammonium salts, namely (NH4)6P2Mo18O62 and (NH4)6P2W18O62, on top of metallic (Al), semiconducting (ITO) and dielectric (SiO2) substrates under ambient conditions is investigated. The respective Keggin heteropolyacids, H3PMo12O40 and H3PW12O40, are also investigated for comparison. On Al substrates, the Wells–Dawson ammonium salts are found to be significantly more reduced (4–6e−) compared to the respective Keggin heteropolyacids (∼2e−), in accordance with their deeper lying lowest unoccupied molecular orbital (LUMO) level. Subsequent thermal treatment in air results in reoxidation of the initially highly reduced POM films. Similar behavior is found on ITO substrates, but in initially less reduced (2–4e−) Wells–Dawson POM films. On the other hand, on SiO2 substrates, the thermal reduction of (NH4)6P2Mo18O62 film is observed and attributed to the thermal oxidation of ammonium counterions by [P2Mo18O62]6− anions. Overall, the multi-electron reduction of Wells–Dawson ammonium salts onto metallic and semiconducting substrates (Al, ITO) is determined by the relative position of the LUMO level of POMs in relation to the Fermi level of the substrate (i.e. substrate work function) and affected in a synergistic way by the presence of ammonium counterions. In contrast, on dielectric substrates (SiO2) the reduction of Wells–Dawson POMs ((NH4)6P2Mo18O62) is attributed only to the oxidation of ammonium counterions.

Zika virus (ZIKV) is an emerging infectious viral pathogen associated with severe fetal cerebral anomalies and the paralytic Guillain-Barre syndrome in adults. It was the cause of a recent global health crisis following its entrance into a naive population in the Americas. Nowadays, no vaccine or specific antiviral against ZIKV is available. In this study, we identified three polyoxometalates (POMs), the Anderson-Evans type [TeW6O24]6- (TeW6), and the Keggin-type [TiW11CoO40]8-_ (TiW11Co), and [Ti2PW10O40]7- (Ti2PW10), that inhibit ZIKV infection with EC50s in the low micromolar range. Ti2PW10, the POM with the greatest selectivity index (SI), was selected and the step of ZIKV replicative cycle putatively inhibited was investigated by specific antiviral assays. We demonstrated that Ti2PW10 targets the entry process of ZIKV infection and it is able to significantly reduce ZIKV progeny production. These results suggest that the polyanion Ti2PW10 could be a good starting point to develop an effective therapeutic to treat ZIKV infection.

The 15-copper(ii)-containing 36-tungsto-4-silicates [Cu15O2(OH)10X(A-α-SiW9O34)4]25- (X = Cl, 1; Br, 2) have been prepared in 70% yield by reaction of the trilacunary 9-tungstosilicate precursor [A-α-SiW9O34]10- with Cu2+ ions in aqueous pH 8 medium. Both polyanions 1 and 2 were isolated as hydrated mixed potassium/sodium salts and characterized in the solid state by FT-IR, TGA, single-crystal XRD, and elemental analysis. DC magnetic susceptibility measurements from 1.8-300 K established the ground state to be paramagnetic with a magnetic moment corresponding to 15 uncoupled Cu2+ (S = 1/2) ions. EPR measurements and simulations were consistent with this analysis. Electrochemical studies were performed for polyanions 1 and 2 dissolved in solution to elucidate the electroactivity of both copper and tungstate sites. Using 2 as a representative example, the electrocatalytic activity towards CO2 reduction upon deposition on a glassy carbon electrode surface, while retaining selectivity relative to hydrogen evolution, was demonstrated.

Here we report on the synthesis and structural characterization of the dithallium(III)-containing 30-tungsto -4-phosphate [Tl