Polyoxometalate-based Framework Research Articles

Anticancer Drug Extraction from Plasma Samples Using Three-Dimensional Polyoxometalate-Based Supramolecular Frameworks as Sorbents.

Four self-assembled inorganic-organic hybrid materials, namely, H{Na(H2O)3[Gd(PDA)(H2O)2]3[BW12O40]}·4H2O (1), H{Na(H2O)3[Tb(PDA)(H2O)2]3[BW12O40]}·3H2O (2), H{Na(H2O)3[Er(PDA)(H2O)3]3[BW12O40]}·H2O (3) (PDA = 1,10-phenanthroline-2,9-dicarboxylate), and [Pr3(H2O)13(pydc-OH)2][BW12O40]·12H2O (4) (pydc-OH = 4-hydroxy-2,6-pyridinedicarboxylate), were hydrothermally synthesized and structurally characterized. Hybrids 1-3 are isostructural and contain a Keggin unit, which is linked to lanthanoids to produce distinct trinuclear lanthanoid building blocks. The fragments are connected by anion-π and hydrogen bonding interactions to create 3D networks. In hybrid 4, a trimeric Pr-organic species bearing a Keggin unit forms a 2D coordination polymer, and then hydrogen bonding interactions between 2D layers lead to the formation of a 3D structure. These polyoxometalate-based frameworks were used as sorbents for the dispersive microsolid-phase extraction (D-μSPE) of two anticancer drugs (doxorubicin and epirubicin) in human plasma samples. Analytes were quantified and separated using high-performance liquid chromatography with fluorescence detection (HPLC-FLD). The method's linearity was between 0.8-500 ng mL-1 and 1.0-500 ng mL-1 for the antineoplastic drugs doxorubicin and epirubicin, respectively. The limits of detection (S/N = 3) were in the range of 0.2-0.3 ng mL-1, while the precision was in the range of 3.5-4.3%. Finally, human plasma samples from patients treated with doxorubicin or epirubicin were analyzed by using the D-μSPE-HPLC-FLD method.

Polyoxometalate-based frameworks as chemical nanoreactors: in situ synthesis of active silver nanoparticles in confined spaces

A novel strategy for the synthesis of Ag@POMOF, that is, well-sized silver nanoparticles confined in a POMOF, has been demonstrated through in situ assembly of silver ions with {Mo36} ions along with reduction.

Polyoxometalate-based frameworks for photocatalysis and photothermal catalysis.

Polyoxometalate-based frameworks (POM-based frameworks) are extended structures assembled from metal-oxide cluster units and organic frameworks that simultaneously possess the virtues of POMs and frameworks. They have been attracting immense attention because of their diverse architectures and charming topologies and also due to their probable application prospects in the areas of catalysis, separation, and energy storage. In this review, the recent progress in POM-based frameworks including POM-based metal organic frameworks (PMOFs), POM-based covalent organic frameworks (PCOFs), and POM-based supramolecular frameworks (PSFs) is systematically summarized. The design and construction of a POM-based framework and its application in photocatalysis and photothermal catalysis are introduced, respectively. Finally, our brief outlooks on the current challenges and future development of POM-based frameworks for photocatalysis and photothermal catalysis are provided.

Opioid Drug Detection in Hair Samples Using Polyoxometalate-Based Frameworks

A series of two-dimensional (2D) polyoxometalate-based frameworks, [Ln3(PDA)3(H2O)6(PMo12O40)]·xH2O (Ln = La (1); Ce (2); Pr (3); Nd (4); PDA = 1,10-phenanthroline-2,9-dicarboxylate), have been synthesized and structurally characterized by various analytical techniques. Single-crystal X-ray diffraction reveals that 1-4 have a unique 2D layer structure in which Keggin anions have coordinated upward and downward the plane, and this feature makes them suitable candidates for surface binding of common drugs via supramolecular and electrostatic interactions. Also, the ability of 1-4 (as the first polyoxomolybdate-containing frameworks) as sorbents for the extraction and quantitative determination of opioid drugs (morphine, methadone, and pethidine) was investigated by using dispersive micro-solid-phase extraction (D-μSPE) and high-performance liquid chromatography (HPLC). The method showed wide linear ranges in the range of 0.3 to 300 ng mg-1 and low limits of detection (LODs) ranged from 0.1 to 0.2 ng mg-1 of hair.

Chaotropic Effect as an Assembly Motif to Construct Supramolecular Cyclodextrin-Polyoxometalate-Based Frameworks.

In aqueous solution, low-charged polyoxometalates (POMs) exhibit remarkable self-assembly properties with nonionic organic matter that have been recently used to develop groundbreaking advances in host-guest chemistry, as well as in soft matter science. Herein, we exploit the affinity between a chaotropic POM and native cyclodextrins (α-, β-, and γ-CD) to enhance the structural and functional diversity of cyclodextrin-based open frameworks. First, we reveal that the Anderson-Evans type polyoxometalate [AlMo6O18(OH)6]3- represents an efficient inorganic scaffold to design open hybrid frameworks built from infinite cyclodextrin channels connected through the disk-shaped POM. A single-crystal X-ray analysis demonstrates that the resulting supramolecular architectures contain large cavities (up to 2 nm) where the topologies are dictated by the rotational symmetry of the organic macrocycle, generating honeycomb (bnn net) and checkerboard-like (pcu net) networks for α-CD (C6) and γ-CD (C8), respectively. On the other hand, the use of β-CD, a macrocycle with C7 ideal symmetry, led to a distorted-checkerboard-like network. The cyclodextrin-based frameworks built from an Anderson-Evans type POM are easily functionalizable using the molecular recognition properties of the macrocycle building units. As a proof of concept, we successfully isolated a series of compartmentalized functional frameworks by the entrapment of polyiodides or superchaotropic redox-active polyanions within the macrocyclic host matrix. This set of results paves the way for designing multifunctional supramolecular frameworks whose pore dimensions are controlled by the size of inorganic entities.

Polyoxometalate-Based Frameworks as Adsorbents for Drug of Abuse Extraction from Hair Samples.

The linkage of molecular components into functional heterogeneous framework materials has revolutionized modern materials chemistry. Here, we use this principle to design polyoxometalate-based frameworks as high affinity adsorbents for drugs of abuse, leading to their application in solid-phase extraction analysis. The frameworks are assembled by the reaction of a Keggin-type polyanion, [SiW12O40]4-, with lanthanoids Dy(III), La(III), Nd(III), and Sm(III) and the multidentate linking ligand 1,10-phenanthroline-2,9-dicarboxylic acid (H2PDA). Their reaction leads to the formation of crystalline 1D coordination polymers. Because of the charge mismatch between the lanthanoids (+3) and the dodecasilicotungstate (-4), we observe incorporation of the PDA2- ligands into crystalline materials, leading to four polyoxometalate-based frameworks where Keggin-type heteropolyanions are linked by cationic {Lnn(PDA)n} groups (Ln = Dy (1), La (2), Nd (3), and Sm (4)). Structural analysis of the polyoxometalate-based frameworks suggested that they might be suitable for surface binding of common drugs of abuse via supramolecular interactions. To this end, they were used for the extraction and quantitative determination of four model drugs of abuse (amphetamine, methamphetamine, codeine, and morphine) by using micro-solid-phase extraction (D-μSPE) and high-performance liquid chromatography (HPLC). The method showed wide linear ranges, low limits of detection (0.1-0.3 ng mL-1), high precision, and satisfactory spiked recoveries. Our results demonstrate that polyoxometalate-based frameworks are suitable sorbents in D-μSPE for molecules containing amine functionalities. The modular design of these networks could in the future be used to expand and tune their substrate binding behavior.

Single-molecule magnets within polyoxometalate-based frameworks.

As an extension of our interest in polyoxometalates (POMs) and lanthanoids, we report the design and synthesis of two polyoxometalate-based frameworks under hydrothermal conditions; [Ho4(PDA)4(H2O)11][(SiO4)@W12O36]·8H2O (1) and [Tb4(PDA)4(H2O)12][(SiO4)@W12O36]·4H2O (2) (H2PDA = 1,10-phenanthroline-2,9-dicarboxylic acid). Both hybrids have been characterized by elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and powder/single-crystal X-ray diffraction. According to the structural analysis, 1 and 2 consist of 2D-cationic coordination polymers based on the respective lanthanoids and PDA2- as well as Keggin anions that reside in the interspaces between two adjacent layers as discrete counterions connected by extensive hydrogen bonding. Although the overall structures of 1 and 2 are composed of cationic and anionic layers, there are many differences in the cationic layers such as various coordination modes of PDA2-, different void shapes, and the existence of dinuclear Tb(III) units only in 2. Frameworks 1 and 2 were further characterized by dc and ac magnetic measurements and both exhibit slow relaxation of magnetization at low temperatures under an applied dc field. Their single-molecule magnet (SMM) properties are investigated, where weak field-induced SMM behaviour is observed at low temperatures in dynamic magnetic studies.

Synthesis and functionality of transition metal-centered polyoxometalate-based crystalline framework materials

Polyoxometalates, a class of discrete nanoscale molecular metal-oxo clusters, have excellent catalytic and photoelectric/electrochromic properties due to their excellent electronic storage and redox capacity. They possess of plenty of potential applications as efficient catalysts in the development of clean and green fuels. However, polyoxometalates are easy to agglomerate and deactivate in the catalytic process, and possess of low specific surface area. Therefore, it is extremely urgent to introduce polyoxometalates into crystalline porous materials with well-defined structure, modifiable channels and high porosity. The introduction of transition metal into polyoxometalates can not only regulate their charge number, but also optimize their band structure. As well known, polyoxometalates, as one kind of unique metal oxide cluster, have been considered as promising secondary building units for construction of porous frameworks because of their adjustable compositions, variable topologies and oxygen-rich surface as well as their diverse physical and chemical properties. Recently, more and more attention has been paid to introducing polyoxometalates into frameworks to functionalize porous frameworks materials. So, these transition metal-centered polyoxometalates should be ideal building units for the design and synthesis of porous crystalline framework materials. These crystalline materials are expected to be used in the fields of single-molecule magnets, photocatalytic water splitting, desulfurization and so on. This review is directed to cover the main advances on the development of transition metal-centered polyoxometalate-based framework materials. In the past several decades, researchers have synthesized 1:12 Keggin type and Silverton type polyoxometalate, Anderson type polyoxometalate Waugh type polyoxometalate, Evans-Showell type polyoxometalate and heteropolyvanadate-based framework materials by hydrothermal method and conventional aqueous solution method. The water oxidation and photocatalytic degradation of organic pollutants of the framework materials were detailly studied. For example, the Keggin anion [CoW12O40]6– turned into an efficient and robust electrocatalyst upon its confinement in the well-defined void space of metal-organic framework (ZIF-8). In the electrocatalytic process, the [H6CoW12O40]@ZIF-8 composite crystalline framework materials is very stable for water oxidation that could retain its initial activity even after 1000 catalytic cycles. The catalyst has a turnover frequency (TOF) of 10.8 mol O2 (mol Co) –1s–1, one of the highest TOFs for electrocatalytic oxygen evolution at neutral pH. Further, the POM-based crystalline framework materials were used for oxidative desulfurization and the decomposition of chemical warfare agent. In these fields, the porous frameworks with catalytic active manganese(IV)-containing heteropolyvanadate [MnV13O38]7- as nodes and rare earth ions as linking units have been successfully prepared. These multifunctional polyoxometalate-based porous framework materials exhibit selective adsorption behavior and remarkable catalytic activity as heterogeneous catalysts for the oxidation of sulfides. A novel manganese(IV)-containing symmetrical heteropolyvanadate K7 [ MnV13O38] · 18H2O to K4Li2[MnV14O40] · 21H2O was also prepared, which is an deficient catalyst for the oxidation of 2-chloroethyl ethyl sulfide with tert-butyl hydroperoxide oxidizing agent. In this catalytic process, a TON of 40 is achieved in 8 h, showing potential application toward air decontamination technology. The results show that the transition metal-centered polyoxometalate-based crystalline framework materials possess of many functionalities, especially as excellent catalysts. In this paper, the research progress of crystalline framework materials constructed from transition metal-centered polyoxometalates is systematically summarized, and the challenges and opportunities in this field are also presented.

ChemInform Abstract: Heterogeneous Epoxidation of Alkenes with H2O2 Catalyzed by a Recyclable Organic—Inorganic Polyoxometalate‐Based Framework Catalyst.

Four organic–inorganic polyoxometalate-based frameworks (HSiW-MOF, PMo-MOF, HPMo-MOF and PW-MOF) were synthesised and characterized by elemental analysis, UV-vis and FT-IR spectroscopy, cyclic voltammetry and XRD analysis. Organic–inorganic polyoxometalate-based frameworks could act as effective and reusable heterogeneous catalysts for selective epoxidation of alkenes with aqueous hydrogen peroxide in acetonitrile. In the presence of PW-MOF, various kinds of alkenes could selectively be converted into the corresponding epoxides with high conversion and selectivity. PW-MOF was stable to leaching, behaved as true heterogeneous catalysts, easily recovered by filtration, and reused four times with maintenance of the catalytic performance.

Selective and Reusable Oxidation of Sulfides to Sulfoxides with Hydrogen Peroxide Catalyzed by Organic–Inorganic Polyoxometalate-Based Frameworks

Several organic–inorganic polyoxometalate-based frameworks such as HSiW-MOF, PMo-MOF, HPMo-MOF and PW-MOF were prepared and characterized by Elemental analysis, UV–Vis, FT-IR and XRD. Thioanisole was used as the model of sulfur compound in the oxidation reaction. The effects of reaction time, type of solvent, amount of catalyst and oxidants in this catalytic system were investigated. At optimum conditions, PMo-MOF and PW-MOF are more active catalysts with respect to H2O2. Oxidation of various sulfides to sulfoxides using 30 % aqueous hydrogen peroxide as oxidant under mild reaction conditions in 90–100 % conversion and 95–100 % selectivity to sulfoxideswas performed. Both catalysts showed high catalytic activity in the oxidation of different sulfides with actively functional groups such as the hydroxyl group and C=C bonds. The heterogeneous catalyst (PW-MOF) could be recovered easily and reused five times without significant loss of its catalytic activity.

Secondary organic moiety templated organic–inorganic polyoxometalate-based frameworks

Four secondary organic moiety templated organic–inorganic polyoxometalate-based framework compounds have been synthesized and characterized.

Heterogeneous epoxidation of alkenes with H2O2 catalyzed by a recyclable organic–inorganic polyoxometalate-based framework catalyst

PW-MOF as an efficient, recyclable and stable catalyst for the selective oxidation of alkenes with hydrogen peroxide.

Polyoxometalate-based frameworks with a linker of paddlewheel diruthenium(ii, iii) complexes

The assembly reactions of a pivalate-bridged paddlewheel diruthenium(II, III) complex, [Ru2II,III(piv)4(THF)2]BF4 (piv = pivalate), with three types of polyoxometalate (POM) clusters, (TBA)2[Mo6O19] (TBA = tetra-n-butylammonium cation; Lindqvist-type Mo6 POM), (TBA)3[H3V10O28] (V10-type POM), and (THA)3[PMo12O40] (THA = tetra-n-hexylammonium cation; Keggin-type Mo12 POM), led successfully to the formation of one-, two-, and three-dimensional (1-, 2-, and 3-D) frameworks composed of [–{Ru2}–POM–] inorganic linkages in (TBA)[{Ru2(piv)4}{Mo6O19}]·CH2Cl2·C2H4Cl2 (1), (TBA)[{Ru2(piv)4}2{H3V10O28}]·C2H4Cl2·7H2O (2), and (THA)[{Ru2(piv)4}2{PMo12O40}]·2(C2H4Cl2) (3), respectively, where 1 is a 1-D linear chain, 2 forms a layered 2-D sheet framework, and 3 constructs a cristobalite-type 3-D structure.

Spontaneous resolution of 3D chiral hexadecavanadate-based frameworks incorporating achiral flexible and rigid ligands

Introducing of mixed flexible and rigid achiral ligands into the hexadecavanadate skeleton leads to the isolation of two enantiomerically 3D chiral hexadecavanadate derivatives, which represent the first example of chiral polyoxometalate-based framework functionalized with mixed flexible and rigid achiral ligands.