Xing Ma

Significant developments in rare-earth-containing polyoxometalate chemistry: synthetic strategies, structural diversities and correlative properties

Owing to their unique and abundant structures and potential multi-fold applications in various fields such as luminescence, magnetism, catalysis, etc., rare-earth-containing polyoxometalates (RECPs) play an important role in the development of polyoxometalate chemistry. In this article, the major progress in RECPs made in the past decade involving synthetic strategies, structural characteristics and some significant properties related to optics, catalysis and magnetism is highlighted and discussed. The final section is committed to looking forward to some future perspectives in this field and providing some personal insights or viewpoints for the ongoing trends in the future.

The first purely inorganic polyoxotungstates constructed from dimeric tungstoantimonate-based iron–rare-earth heterometallic fragments

The rational self-assembly of a trilacunary Keggin precursor with Fe3+ and RE3+ (rare-earth) ions via a conventional aqueous solution method has led to a series of novel tungstoantimonate-based Fe–RE heterometallic derivatives [Pr(H2O)8][Pr(H2O)6][Fe4(H2O)10(B-β-SbW9O33)2]·16H2O (1) and [RE(H2O)7]2[Fe4(H2O)10(B-β-SbW9O33)2]·22H2O [RE = TbIII (2), DyIII (3), LuIII (4), YIII (5)], which have been further structurally characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD), single-crystal X-ray diffraction and thermogravimetric (TG) analysis. To the best of our knowledge, 1–5 represent the first purely inorganic Fe–RE heterometallic tungstoantimonates based on the trilacunary Keggin [B-β-SbW9O33]9− unit. In 1, the tetra-FeIII substituted sandwich-type unit [Fe4(H2O)10(B-β-SbW9O33)2]6− is built up of two trilacunary Keggin subunits [B-β-SbW9O33]9− sandwiching a rhomb-like {FeIII4} cluster, and then the disordered PrIII cations work as bridges that link adjacent sandwich-type units [Fe4(H2O)10(B-β-SbW9O33)2]6−, giving rise to the first 2-D extended sheet based on tungstoantimonate fragments and Fe–RE heterometallic cations. 2–5 are isomorphic and exhibit a discrete structure composed of a tetra-FeIII substituted sandwich-type unit [Fe4(H2O)10(B-β-SbW9O33)2]6− and two supporting [RE(H2O)8]3+ cations. The electrochemical and electrocatalytic properties of 1 and 2 have been investigated in detail in a 0.5 mol L−1 Na2SO4 + H2SO4 supporting electrolyte, and both 1 and 2 illustrate obvious electrocatalytic activity toward the reduction of NO2− and BrO3−.

Lanthanide-Connecting and Lone-Electron-Pair Active Trigonal-Pyramidal-AsO3 Inducing Nanosized Poly(polyoxotungstate) Aggregates and Their Anticancer Activities.

By virtue of the stereochemical effect of the lone-electron pair located on the trigonal-pyramidal-AsO3 groups and the one-pot self-assembly strategy in the conventional aqueous solution, a series of novel lanthanide-bridging and lone-electron-pair active trigonal-pyramidal-AsO3 inducing nanosized poly(polyoxotungstate) aggregates [H2N(CH3)2]6 Na24H16{[Ln10W16(H2O)30O50](B-α-AsW9O33)8}·97H2O [Ln = EuIII (1), SmIII (2), GdIII (3), TbIII (4), DyIII (5), HoIII (6), ErIII (7), TmIII (8)] were prepared and further characterized by elemental analyses, IR spectra, UV spectra, thermogravimetric (TG) analyses and single-crystal X-ray diffraction. The most remarkable structural feature is that the polyanionic skeleton of {[Ln10W16(H2O)30O50](B-α-AsW9O33)8}46− is constructed from eight trivacant Keggin [B-α-AsW9O33]9− fragments through ten Ln centers and sixteen bridging W atoms in the participation of fifty extraneous oxygen atoms. Notably, 4 and 8 can be stable in the aqueous solution not only for eight days but also in the range of pH = 3.9–7.5. Moreover, the cytotoxicity tests of 4 and 8 toward human cervical cancer (HeLa) cells, human breast cancer (MCF–7) cells and mouse fibroblast (L929) cells were performed by the 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and the cell apoptosis processes were characterized by calcein AM/PI staining experiments, annexin V-FITC/PI staining experiments and morphological changes.

Syntheses, structures and fluorescence properties of three rare-earth containing docosatungstates.

Three rare-earth containing docosatungstates Na3H2[RE(H2O)4][RE(H2O)5]2[W22O74H2]·36H2O [RE=DyIII (1), HoIII (2), YIII (3)] have been synthesized by reaction of Na2WO4·2H2O, dimethylamine hydrochloride (DMAHC) and RE(NO3)3·6H2O in the aqueous solution and characterized by elemental analyses, IR spectra, thermogravimetric (TG) analysis, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. 1-3 are isomorphous and each molecular unit consists of a S-shaped docosatungstate [W22O74H2]14- polyoxoanion with two supporting [RE(H2O)5]3+ cations and one disordered [RE(H2O)4]3+ cation. The [W22O74H2]14- polyoxoanion can be viewed as combination of two hendecatungstate [W11O38H]9- subunits in the staggered fashion by sharing two μ2-O atoms. The TG curves of 1-3 reveal the one-step weight loss between 25°C to 700°C. Moreover, both 1 and 2 demonstrate the characteristic luminescence emission behaviors of the corresponding RE3+ ions and their lifetime decay curves can be well fitted to the double exponential function. In addition, the CIE chromaticity coordinates of 1 and 2 have been obtained based on their corresponding emission spectra, and their dominant wavelengths and color purities have been also calculated.