Two U(VI)-Containing Silicotungstates with Sandwich Structures: Lewis Acid–Base Synergistic Catalyzed Synthesis of Benzodiazepines and Pyrazoles

Electrocatalytic Hydrogen Evolution by a Uranium(VI) Polyoxometalate: an Environmental Toxin for Sustainable Energy Generation

The uranyl ion (UO2)2+, a uranium nuclear waste, is one of the serious contaminants in our ecosystem because of its radioactivity, relevant human activities, and highly mobile and complex nature of living cells. In this article, we have reported the synthesis and structural characterization of an uranyl cation-incorporated polyoxometalate (POM) compound, K10[{K4(H2O)6}{UO2}2(α-PW9O34)2]·13H2O (1), in which the uranyl cations are complexed with an in situ generated [α-PW9O34]9- cluster. Single-crystal X-ray diffraction (SCXRD) analysis of compound 1 reveals that the uranyl-potassium complex cationic species, [{K4(H2O)6}{UO2}2]8+, is sandwiched by two [α-PW9O34]9- clusters resulting in a Dawson type of POM. Compound 1 was further characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis and infrared (IR), Raman, electronic absorption, and solid-state photoluminescence spectral studies. IR stretching vibrations at 895 and 856 cm-1 and the Raman signature peak at 792 cm-1 in the IR and Raman spectra of compound 1 primarily confirm the presence of a trans-[O═U═O]2+ ion. The solid-state photoluminescence spectrum of 1 exhibits a typical vibronic structure, resulting from symmetrical vibrations of [O═U═O]2+ bands, corresponding to the electronic transitions of S11 → S10 and S10 → S0υ (υ = 0-3). Interestingly, title compound 1 shows efficient electrocatalytic hydrogen evolution by water reduction with low Tafel slope values of 186.59 and 114.83 mV dec-1 at 1 mA cm-2 along with optimal Faradaic efficiency values of 82 and 87% at neutral pH and in acidic pH 3, respectively. Detailed electrochemical analyses reveal that the catalytic hydrogen evolution reaction (HER) activity mediated by compound 1 is associated with the UVI/UV redox couple of the POM. The microscopic as well as routine spectral analyses of postelectrode samples and controlled experiments have confirmed that compound 1 behaves like a true molecular electrocatalyst for the HER. To our knowledge, this is the first paradigm of a uranium-containing polyoxometalate that exhibits electrocatalytic water reduction to molecular H2. In a nutshell, an environmental toxin (a uranium-oxo compound) has been demonstrated to be utilized as an efficient electrocatalyst for hydrogen generation from water, a green approach of sustainable energy production.

An Unusual Bismuth-Antimony-Europium Cluster-Imbedded Polyoxotungstate and Its Bidirectional Luminescence Detection

An unprecedented aggregate formed by two bismuth-antimony-europium cluster-imbedded tungsten-oxo clusters and one Krebs-type polyoxotungstate linker [H2N(CH3)2]14Na30H6[W4O10][B-β-BiW9O33]2{[Bi5.35Sb0.65Eu3O9(H2O)9][B-α-SbW9O33]3}2·124H2O (1) was prepared. The polyoxoanion skeleton of 1 contains a Krebs-type polyoxotungstate [W4O10][B-β-BiW9O33]2}14- ({Bi2W22}) (1a) as a linker that offers six active coordinate O atoms (two μ3-O and four μ2-O atoms) to grasp two Bi-Sb-Eu cluster-imbedded tungsten-oxo clusters {[Bi5.35Sb0.65Eu3O9(H2O)9][B-α-SbW9O33]3}18- (1b) through Bi-O-W and Sb-O-W bonds. 1b comprises an unprecedented nona-nuclearity Bi-Sb-Eu [Bi5.35Sb0.65Eu3O9(H2O)9]9+ cluster encircled by three trivacant [B-α-SbW9O33]9-segments in a triangular motif through Eu-O-W, Sb-O-W, and Bi-O-W linkages into a trilobal trimer. Moreover, a bidirectional detection method by using 1 as an effective luminescence probe was proposed to recognize both Mn2+ and CO32- through an "on-off-on" mode. 1 can be used as an "on-off" luminescent sensor to detect Mn2+ ions in aqueous solution. The limit of detection was 0.05 μM (9 × 10-6 mg L-1), which is much lower than the World Health Organization (WHO) guideline for Mn2+ concentration in drinking water (0.05 mg L-1). Then the Mn2+-quenching system can be used as an "off-on" sensor to detect CO32- in water system. This work provides a new research idea for the application of rare-earth-imbedded polyoxotungstate-based materials in the field of optical smart detection.

Three rare-earth incorporating 6-peroxotantalo-4-selenates and catalytic activities for imidation reaction

Functionalization with belt lanthanide groups allows for the crystallization and structural characterization of homometallic selenotantalates, CsK[Ln(H2O)6Se4(TaO2)6(OH)3O18]·nH2O (Ln = Eu/Gd, n = 14 (STD-Eu, STD-Gd) and Ln = Lu, n = 12 (STD-Lu)). The basket-shaped {Se4(TaO2)6} archetype is assembled in a simple one-pot reaction of Na2SeO3 and K8[Ta6O19]·17H2O in acidic aqueous medium (pH 2) and in the presence of hydrogen peroxide. This unit has been proven to be an effective precursor for the preparation of a range of new POMs containing the {Se4(TaO2)6} unit. The lanthanide derivatives STD-Eu, STD-Gd and STD-Lu have been fully characterized with single-crystal X-ray diffraction, IR spectroscopy, TG analysis and PXRD in the solid state. The photoluminescence and lifetime decay behaviours of STD-Eu have been studied at room temperature, and the photoluminescence spectrum displays the characteristic emission of the Eu3+ cation. In addition, the catalytic activities of STD-Eu, STD-Gd and STD-Lu on the reaction of phthalic anhydride with phenylamines have been investigated. STD-Eu shows good catalytic activities for imidation reactions.