Dongdi Zhang

Nona-copper(II)-containing 18-tungsto-8-arsenate(III) exhibits antitumor activity

The nona-Cu(II)-containing tungstoarsenate(III) [H4{Cu(II)9As(III)6O15(H2O)6}(α-As(III)W9O33)2](8-) (1a) has been synthesized and characterized. Polyanion 1a comprises a unique, cylindrical {Cu(II)9As(III)6O15(H2O)6}(6+) cluster, which forms a large central cavity and is capped on either end by an [α-As(III)W9O33](9-) capping group. It exhibits remarkable activity against K562 leukaemia cells, as well as induces HepG2 cell apoptosis and autophagy.

Three-dimensional lanthanide polyoxometalate organic complexes: correlation of structure with properties

A family of three-dimensional (3D) architectures based on lanthanide-substituted polyoxotungstate building blocks [Ln(HL)(L)(H2O)6{Ln(H2L)0.5(α-PW11O39H)Ln(H2O)4}]2·nH2O (Ln = La, n = 8 (1); Ln = Ce, n = 12 (2); Ln = Pr, n = 8 (3); H2L = 2,5-pyridinedicarboxylic acid) have been successfully synthesized under hydrothermal conditions and further characterized by elemental analyses, X-ray powder diffraction (XRPD), IR spectra, UV spectra, thermogravimetric (TG) analyses and single-crystal X-ray diffraction. The common features of 1–3 are that they all consist of 1D zigzag chain [{Ln(α-PW11O39H)}2]6− moieties and the chains further form into 3D structure via metal–organic cations. Furthermore, the photocatalysis properties of 1–3 for degradation of the rhodamine-B (RhB) upon 500 W Hg lamp irradiation have been examined. The magnetic properties of compounds 2 and 3 have been studied by measuring their magnetic susceptibility in the temperature range of 2–300 K.

Tetradecacobalt(II)-containing 36-niobate [Co14(OH)16(H2O)8Nb36O106]20- and its photocatalytic H2 evolution activity.

A gigantic Co14-containing 36-niobate, Na12K8[Co14(OH)16(H2O)8Nb36O106]⋅71H2O (1), has been prepared by the hydrothermal method and structurally characterized. Polyanion [Co14(OH)16(H2O)8Nb36O106](20-) (1 a) comprises a central Co7 core, surrounded by another seven isolated Co(2+) ions and six Lindqvist-type (Nb6O19) hexaniobate fragments. This is the first example of a high-nuclear cobalt-cluster-containing polyoxoniobate. The photocatalytic H2 evolution activity of Pt-loaded 1 was observed in methanol solution under irradiation using a 300 W Xe lamp.

Magnetic double-tartaric bridging mono-lanthanide substituted phosphotungstates with photochromic and switchable luminescence properties

A series of inorganic–organic hybrid double-tartaric bridging mono-lanthanide substituted phosphotungstates with a general formula of [N(CH3)4]6K3H7[Ln(C4H2O6)(α-PW11O39)]2·27H2O (Ln = Dy for 1Dy, Er for 2Er, and Yb for 3Yb) have been synthesized by the reactions of K14[P2W19O69(H2O)]·24H2O and LnCl3·6H2O in the presence of tartaric acid and tetramethyl ammonium counterions in an aqueous medium. Crystal structure analyses reveal that 1Dy–3Yb are isomorphic and are all built from two mono-lanthanide substituted Keggin polyoxoanion fragments joined together by two tartaric ligands. 1Dy–3Yb exhibit reversible photochromism and they can change from white (for 1Dy and 3Yb) or pink (for 2Er) to blue upon UV irradiation and then their colors gradually recover in the dark for about five days. The solid-state photoluminescence spectra of 1Dy–3Yb display their characteristic emissions of lanthanide components based on their 4f–4f transitions. Moreover, the fluorescence of 1Dy displays an effectively switchable behaviour when exposed to UV light, the intensity of the emission band at 573 nm gradually weakens as the irradiation time increases and the intensity drops to 2.4% of the original intensity after 30 minutes. It is noteworthy that the frequency dependence of the ac-susceptibility was found for 1Dy, suggesting a typical single-molecule magnet (SMM) behavior with an energy barrier of 20 K.

Coordination-Driven Self-Assembly of a 2D Graphite-Like Framework Constructed from High-Nuclear Ce10 Cluster Encapsulated Polyoxotungstates

It is challenging to explore and prepare high-nuclear lanthanide (Ln) cluster-encapsulated polyoxometalates (POMs). Herein, we fabricate an unprecedented Ce10-cluster-embedded polyoxotungstate (POT) (TMA)14H2[Ce(III)(H2O)6]{[Ce(IV)7Ce(III)3O6(OH)6(CO3)(H2O)11][(P2W16O59)]3}·41H2O (1) (TMA = tetramethyleneamine) by coordination-driven self-assembly strategy, which contains the largest Ce cluster [Ce(IV)7Ce(III)3O6(OH)6(CO3)(H2O)11] (Ce10) in all the Ln-containing POM chemistry to date. Self-assembly of the in situ dilacunary [P2W16O59](12-) fragments and mixed Ce(3+) and Ce(4+) ions by means of coordination-driven force results in a novel 2D graphite-like framework constructed from mixed-valent cerium(III/IV) cluster {Ce10} encapsulated poly(POT) units and Ce(3+) ions. The most remarkable feature is that the skeleton of the centrosymmetric Ce10-cluster-embedded POT trimer contains three dilacunary [P2W16O59](12-) fragments trapping a novel {Ce10} cluster via 18 terminal-oxo and three μ4-oxo atoms.

A New Nb28 Cluster Based on Tungstophosphate, [{Nb4O6(OH)4}{Nb6P2W12O61}4]36–

A structurally intriguing polyanion, [{Nb4O6(OH)4}{Nb6P2W12O61}4](36-) (2), was directly formed by controlling the reaction parameters and characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analyses. Polyanion 2 is the first niobium-substituted Wells-Dawson-based tetramer and contains the largest Nb28 cluster encapsulated by four hexalacunary Wells-Dawson frameworks. The activities of compounds Na12[H24-2]·24H2O (2a), K12[H2P2W12O48]·24H2O, and K7[HNb6O19]·13H2O against three human tumor cell lines were investigated in vitro. The preliminary results revealed that 2a could efficiently inhibit the growth of the human breast cancer MCF-7 cells. Interestingly, the activity of 2a is significantly better than those of the simple reagents.

A {Co4O4} Cubane Incorporated within a Polyoxoniobate Cluster

A novel octacobalt-containing polyoxoniobate, Na6 K12 [H2 Co8 O4 (Nb6 O19 )4 ]⋅39 H2 O, has been prepared by a combination of hydrothermal and diffusion methods. The polyanion [H2 Co8 O4 (Nb6 O19 )4 ](18-) incorporates a tetrameric assembly of Lindqvist-type [Nb6 O19 ](8-) fragments trapping a {Co(II) 4 Co(III) 4 } cluster which comprises a central {Co(III) 4 O4 } cubane core, surrounded by another four Co(II) ions linkers. Furthermore, magnetic measurements show that the compound exhibits antiferromagnetic interactions.

A {Nb6P2W12}-Based Hexameric Manganese Cluster with Single-Molecule Magnet Properties

By deliberately using a metastable polyanion [(NbO2 )6 P2 W12 O56 ](12-) (1), which was formed in situ, we have discovered the unprecedented hexameric cluster {Mn15 (Nb6 P2 W12 O62 )6 } (2), in which the six polyanions [Nb6 P2 W12 O61 ](10-) are alternately connected by four intriguing trinuclear {Mn(III) 3 } moieties and four {Mn(II) } linkers. This discovery is the first in which the phosphoniobotungstate has been made accessible by using transition-metal ions; furthermore, polyanion 2 represents the largest niobotungstate cluster reported to date. Analysis by means of electrospray ionization mass spectrometry (ESI-MS) provides insight into the self-assembly process, and the peaks observed relate to the different charge states of the parent cluster, thus confirming the stability of 2. In addition, magnetic-susceptibility measurements reveal that each {Mn(III) 3 } subunit is a separate single-molecule magnet (SMM). This discovery results from the exploration of the reverse effect of metastable polyanion 1 possessing high reactivity, thereby turning a disadvantage into an advantage. This finding could define a new synthetic strategy for the design and synthesis of magnetic polyoxometalate (POM) clusters.

An unprecedented trimer based on monovacant Dawson anion: [(α2-P2W17O61)Ln(H2O)4]321− (Ln = LaIII, CeIII and PrIII)

Three unprecedented trimers based on monovacant Dawson-type polyoxotungstates Na12[Ln(H2O)9]2[(α2-P2W17O61H4)La(H2O)4]6·100H2O (Ln = LaIII (1)) and Na24[Ln(H2O)8]2[(α2-P2W17O61H2)Ln(H2O)4]6·56H2O (Ln = CeIII (2), and PrIII (3)) have been successfully synthesized by straightforward “self assembly” processes starting from a 1 : 4 ratio of the saturated Dawson precursor [α-P2W18O62]6− and Ln ions in aqueous solution, which were further characterized by elemental analyses, X-ray powder diffraction (XRPD), IR spectra, thermogravimetric (TG) analyses, electrospray ionization mass spectrometry (ESI-MS) and single-crystal X-ray diffraction. The common feature of 1–3 is that they all consist of the trimeric triangular [(α2-P2W17O61)Ln(H2O)4]321− subunit, as we know, the trimeric [(α2-P2W17O61)Ln(H2O)4]321− polyoxoanion is firstly discovered. Furthermore, all three compounds can further generate three dimensional channel architectures through Na+ cations. Meanwhile, the multinuclear solution 31P NMR spectrum of 1 at 300 K in D2O has been investigated, the results are further demonstrated by the technologies of ESI-MS.

Two new members of the niobium-substituted polytungstophosphate family based on hexalacunary [H2P2W12O48]12− building blocks

Two structurally novel nanoscale clusters [{Nb6(O2)4P2W12O57}2]20− (1) and [{P2W12Nb7O63(H2O)2}4{Nb4O4(OH)6}]30− (2) were synthesized under specific reaction conditions. Cluster 1 displays an unprecedented di-Nb–O–Nb-linked Wells–Dawson dimer, whilst cluster 2 contains the highest nuclearity niobium containing heteropolyoxometalate to date. Furthermore, 31P and 183W NMR spectra indicate that the polyanion 2 remains stable in solution. The photocatalytic activities of the respective salts 1a, 2a and K6[α-P2W18O62]·14H2O for H2 evolution were evaluated. The enhanced photocatalytic activity of 2a may be attributed to the incorporation of Nb into the polyoxotungstate framework.