Polyoxometalate-based Coordination Polymers Research Articles

POMCPs with Novel Two Water-Assisted Proton Channels Accommodated by MXenes for Asymmetric Supercapacitors.

To develop high-performance supercapacitors, the negative electrode is at present viewed as one of the most challenging tasks for obtaining the next-generation of energy storage devices. Therefore, in this study, a polyoxometalate-based coordination polymer [Zn(itmb)3 H2 O][H2 SiW12 O40 ]·5H2 O (1) is designed and prepared by a simple hydrothermal method for constructing a high-capacity negative electrode. Polymer 1 has two water-assisted proton channels, which are conducive to enhancing the electrical conductivity and storage capacity. Then, MXene Ti3 C2 Tx is chosen to accommodate coordination polymer 1 as the interlayer spacers to improve the conductivity and cycling stability of 1, while preventing the restacking of MXene. Expectedly, the produced composite electrode 1@Ti3 C2 Tx shows an excellent specific capacitance (1480.1 F g-1 at 5 A g-1 ) and high rate performance (a capacity retention of 71.5% from 5 to 20 A g-1 ). Consequently, an asymmetric supercapacitor device is fabricated using 1@Ti3 C2 Tx as the negative electrode and celtuce leaves-derived carbon paper as the positive electrode, which demonstrates ultrahigh energy density of 32.2Wh kg-1 , and power density 2397.5 W kg-1 , respectively. In addition, the ability to illuminate a red light-emitting diode for several minutes validates its feasibility for practical application.

Highly Efficient Synthesis of p-Benzoquinones Catalyzed by Robust Two-Dimensional POM-Based Coordination Polymers.

Selective oxidation of alkyl-substituted phenols offers efficient access to p-benzoquinones (BQs) that serve as key components for synthesizing biologically active compounds, but rational manufacture of efficient recyclable catalysts for such a reaction remains a severe challenge. Herein, two crystalline 2D polyoxometalate-based coordination polymers (POMCPs), formulated as H3[CuI3(L)3]2[PM12O40]·xH2O (M = Mo, x = 4 for 1; M = W, x = 6 for 2; and HL = 4-(1H-tetazol-5-yl)pyridine), are prepared by a mineralizer-assisted one-step synthesis strategy and explored as heterogeneous catalysts for p-BQs synthesis. Both compounds have been characterized through elemental analysis, EDS analysis, infrared spectroscopy, UV-vis diffuse reflectance spectrum, EPR, XPS, BET, single-crystal, and powder X-ray diffraction. Single-crystal X-ray diffraction analysis indicates that both 1 and 2 exhibit an interesting 2D sheet structure composed of 2-connected Keggin type anions [PM12O40]3- and hexa-nuclear {CuI6(HL)6} cluster-based metal-organic chains via Cu···O interactions. When used as catalysts, POMCPs 1 and 2 have excellent catalytic activities in the selective oxidation of substituted phenols to p-BQs with H2O2. Notedly, in the model reaction from 2,3,6-trimethylphenol (TMP) to the vitamin E key intermediate trimethyl-p-benzoquinone (TMBQ), the catalytic activities expressed by turnover frequency (TOF) of 1 and 2 can reach an unprecedented 2400 and 2000 h-1, respectively, at close to 100% TMBQ yield. The truly heterogeneous nature, stability, and structural integrity of both catalysts were ascertained by FTIR, PXRD techniques, and the following cycles. Mechanism studies reveal that both catalysts can involve a dual reaction pathway through a heterolytic oxygen atom transfer mechanism and homolytic radical mechanism. Moreover, the 2D POMCPs with highly accessible bilateral active sites and efficient mass transfer efficiency possess superior catalytic performance to their analogous 3D species.

Self-assembly of three novel entangled polyoxometalate-based coordination polymers with redox properties

Three novel entangled coordination polymers (CPs), namely, [Cu4(BPB)5(HPW12O40)2]·2H2O (JOU-15), [Cu3(BPB)3PW12O40] (JOU-16), and [Cu3(BPBP)3PW12O40] (JOU-17), have been successfully synthesized by combining flexible N-donor ligands and Keggin type polyoxometalates with copper ion under hydrothermal conditions. Structural characterizations show that JOU-15 features an unusual 1D + 1D → 2D entangled network with the coexistence of polycatenation and interdigitation. JOU-16 exhibits a fascinating self-catenated three-dimensional framework with a new point symbol of (44·610·8)(65·8)(66). JOU-17 displays a novel 1D + 3D + 3D → 3D entangled framework with features of both polycatenation and polythreading. In addition, the electrochemical properties of these compounds have also been studied.

A High-Capacity Negative Electrode for Asymmetric Supercapacitors Based on a PMo12 Coordination Polymer with Novel Water-Assisted Proton Channels.

The development of a negative electrode for supercapacitors is a critical challenge for the next-generation of energy-storage devices. Herein, two new electrodes formed by the coordination polymers [Ni(itmb)4 (HPMo12 O40 )]·2H2 O (1) and [Zn(itmb)3 (H2 O)(HPMo12 O40 )]·4H2 O (2) (itmb = 1-(imidazo-1-ly)-4-(1,2,4-triazol-1-ylmethyl)benzene), synthesized by a simple hydrothermal method, are described. Compounds 1 and 2 show high capacitances of 477.9 and 890.2 F g-1 , respectively. An asymmetric supercapacitor device assembled using 2 which has novel water-assisted proton channels as negative electrode and active carbon as positive electrode shows ultrahigh energy density and power density of 23.4 W h kg-1 and 3864.4 W kg-1 , respectively. Moreover, the ability to feed a red light emitting diode (LED) also demonstrates the feasibility for practical use. The results allow a better elucidation of the storage mechanism in polyoxometalate-based coordination polymers and provide a promising direction for exploring novel negative materials for new-generation high-performance supercapacitors.

Highly dispersive bimetallic sulfides afforded by crystalline polyoxometalate-based coordination polymer precursors for efficient hydrogen evolution reaction

Molybdenum disulfide (MoS2) is viewed as one of the most promising hydrogen evolution reaction (HER) electrocatalyst thanking to its graphene-like layered structure and suitable hydrogen chemisorption free energy. However, its application is still hindered by some obstacles, such as less exposed active sites and poor inherent conductivity. Herein, two new crystalline polyoxometalate-based metal-organic polymers with Co/Ni and Mo, {(C2H2N3)3Co2·6H2O}[H3SiMo12O40]·9H2O (1) and {(C2H2N3)3Ni2·6H2O}[H3SiMo12O40]·5H2O (2) (1,2,4-triazole = C2H2N3) are firstly designed and fabricated, and characterized by sufficient technologies including single-crystal X-ray diffraction and so on. And they are directly utilized as ‘preassembly platform’ reacting with thiourea to synthesize highly dispersive CoS2–MoS2 and Ni3S2–MoS2 bimetallic sulfides with mesoporous structure. In virtue of the synergistic effects, and high dispersiveness and porosity of CoS2/Ni3S2 and MoS2 in carbon cloth (CC), 50%CoS2–MoS2@CC and 50%Ni3S2–MoS2@CC composites display a low overpotential of 222 and 224 mV at 10 mA cm−2, and a small Tafel slope of 64.2 and 65.7 mV·dec−1 in H2SO4 solution, respectively. Such superior electrocatalytic HER performances outperform most of both POM-based and MoS2-based non-noble metal catalysts. Hence, this work presents a facile tactic for engineering highly dispersive bimetallic sulfides with excellent electrocatalytic HER performance.

RETRACTED: Two polyoxometalate-based coordination polymers: Synthesis, characterization and in vitro anti-lung cancer activity

This article has been retracted, and the online PDF has been watermarked “RETRACTION”. The retraction notice is available at http://doi.org/10.3233/MGC-220954.

Multiunit Catalysts with Synergistic Reactivity: Three-Dimensional Polyoxometalate-Based Coordination Polymers for Highly Efficient Synthesis of Functionalized p-Benzoquinones.

The rational design of highly efficient catalysts for the synthesis of functionalized p-benzoquinones (p-BQs) is of great significance for the manufacture of bioactive compounds. Herein, two 3D crystalline polyoxometalate-based coordination polymers (POMCPs) are used as heterogeneous catalysts for the synthesis of p-BQs, which are H[CuII(ttb)(H2O)3]2[CuII(ttb)Cl]2[PW12O40]·4H2O (1) (Httb = 1-(tetrazol-5-yl)-4-(triazol-1-yl)benzene) and [ClCu6I(trz)4][ClCu5I(trz)4]2[CuII(H2O)][PW12O40] (2) (trz = 1,2,4-triazole). Both compounds were characterized by elemental analysis, IR, XPS, solid diffuse reflective spectroscopy, TG analysis, and single-crystal X-ray diffraction. In 1, Keggin anions [PW12O40]3- locate in 1D square channels constructed from wave-like Cu-ttb layers to form a 3D POMCP by coordinating to Cu ions, and in 2, [PW12O40]3- anions situate in eight-membered Cu-trz channels via Cu···O interactions to yield a 3D POMCP structure. The catalytic activities of 1 and 2 have been evaluated in the selective oxidation of alkylphenols/alkoxybenzenes/methylnaphthalene, especially in the oxidation reaction of 2,3,6-trimethylphenol (TMP) to 2,3,5-trimethyl-p-benzoquinone (TMBQ, vitamin E key intermediate), with H2O2 as oxidant. By using catalysts 1 and 2 under optimal conditions, the yield of TMBQ can reach 99% and 96% within 10-20 min, respectively. Both catalysts demonstrated high turnover frequencies (300 h-1 for 1 and 600 h-1 for 2) and the truly heterogeneous nature. 1 and 2 catalyzed the synthesis of p-BQs on the basis of effective cooperative catalytic activities by POMs and metal nodes.

Synthesis and characterization of a new (1D+1D) polyoxometalate-based polypseudo-rotaxane coordination polymer

A new polyoxometalate-based coordination polymer, Ag2(L)2(VW12O40)][Ag2(L)2]·4H2O (1) {L = 3,5-di(1H-1,2,4-triazol-1-yl)benzoic acid}, has been isolated under hydrothermal conditions and characterized by routine methods. Compound 1 exhibits an interesting 1D + 1D polypseudo-rotaxane architecture, as shown by X-ray diffraction analysis. The new compound represents a scarce example of 1D + 1D polypseudo-rotaxane architecture, namely, ladder motifs are threaded by zigzag chains rather than a straight one. The coordination stability around loop and thread motifs was investigated to expatiate on the zigzag chained polypseudo-rotaxane. In addition, crystal 1 can be used as a packing material to selectively adsorb cationic dyes such as crystal violet (CV) and methylene blue (MB) concomitant with methyl orange anionic dyes with high uptakes and rapid adsorption rate.

Assembly, disassembly and reassembly: a "top-down" synthetic strategy towards hybrid, mixed-metal {Mo10Co6} POM clusters.

Polyoxometalates (POMs) are commonly prepared using a "bottom-up" synthetic procedure. The alternative "top-down" approach of disassembling a pre-formed POM unit to generate new synthetic intermediates is promising, but relatively comparatively underused. In this paper, a rationale for the top-down method is provided, demonstrating that this approach can generate compounds that are fundamentally inaccessible from simple bottom-up assembly. We demonstrate this principle through the synthesis of a series of 10, new, mixed-metal, hybrid compounds with the general formula [TBA]2[MoVI10CoII6O30(RpPO3)6(RcCOO)2(L)x(H2O)6] (TBA = tetrabutylammonium, Rp = phosphonate moiety, Rc = carboxylate moiety, L = pyridyl ligand, and x = 2-4), including a one-dimensional polyoxometalate-based coordination polymer. We propose that these structures are generated from {MoxO3x-1} fragments that cannot be accessed from bottom-up assembly alone. The POM clusters are stabilised by three distinct classes of organic ligand - organophosphonate, carboxylate and pyridyl ligands - which can each be substituted independantly, thus providing a controlled route to ligand functionalisation.

PH-dependent assembly of two polyoxometalate-based coordination polymers: structures and electrocatalytic properties

Two new polyoxometalate-based coordination polymers have been synthesized at different pHs under identical hydrothermal conditions, (Hbib)[Cu2(bib)2(PMo12O40)] (1) and (Hbib)2[Cu(bib) (PMo12O40)]·2H2O (2) (bib = 4-bis(imidazol-1-yl) benzene). Their structures were determined by single crystal X-ray diffraction analyses and characterized by routine methods. When the pH was adjusted to 2.0 − 2.5, 1 was obtained, which exhibits a 1-D rail-like chain. Compound 2 was obtained at pH of 2.5 − 3.2 and exhibits a 2-D layer with (44) sql net. The pH of the reaction plays a key role in the assembly of the polyoxometalate-based coordination polymer. The electrochemical experiments indicate that 2-based carbon paste electrode possesses high catalytic efficiency and high stability towards reduction of iodate and oxidation of ascorbic acid.

Effect of Cations on the Structure and Electrocatalytic Response of Polyoxometalate-Based Coordination Polymers

A series of six hybrid polymers based on the mixed-valent {e-PMoV8MoVI4O40Zn4} (eZn) Keggin unit have been synthesized under hydrothermal conditions using tritopic (1,3,5-benzenetricarboxylate (trim) or 1,3,5-benzenetribenzoate (BTB)) or ditopic (4,4′-biphenyldicarboxylate (biphen)) linkers and [M(bpy)3]2+ (M = Co, Ru) complexes as charge-compensating cations. (TBA)2[Co(C10H8N2)3][PMo12O37(OH)3Zn4](C27H15O6)4/3·1.5C27H18O6·24H2O (Co-e(BTB)4/3) has a three-dimensional (3D) framework with two interpenetrated networks and is isostructural to (TBA)4[PMo12O37(OH)3Zn4](C27H15O6)4/3·1.5C27H18O6·8H2O (e(BTB)4/3). In Co-e(BTB)4/3, two tetrabutylammonium (TBA+) cations over the four present in e(BTB)4/3 are replaced by one [Co(bpy)3]2+ complex. [Co(C10H8N2)3][PMo12O37(OH)3Zn4](C9H3O6)Co(C10H8N2)4(H2O)·16H2O (Co-e(trim) (bpy)2) is a 1D coordination polymer with two types of CoII-containing complexes, one covalently attached to the 1D chains and the other located in the voids as the counterion. [Ru(C10H8N2)3]4[PMo12O...

The first two-fold interpenetrating polyoxometalate-based coordination polymer with helical channels: structure and catalytic activities

A polyoxometalate-based coordination polymer POMCP-1 with a [helix + interpenetration] double configuration was successfully isolated, which shows effective catalytic activities for the esterification reaction and the photodecomposition of Rhodamine-B.

Two polyoxometalate-based coordination polymers constructed from Mn(II)-4,4′-bipyridine-N,N′-dioxide building blocks and Keggin-type clusters: Syntheses, crystal structures and spectral properties

Two polyoxometalate-based coordination polymers {[Mn2(dpdo)4(H2O)6](GeMo12O40)(H2O)4}n (1) and {[Mn2(dpdo)4(H2O)6](GeW12O40)(H2O)3}n (2) (dpdo=4,4′-bipyridine-N,N′-dioxide) have been synthesized and characterized by IR, elemental analysis, XRPD, TG technique and X-ray crystallography. The polymers 1 and 2 are basically isostructural and feature a 3D supramolecular framework decorated with Keggin-type polyanion clusters based on one-dimension polymeric chains, which formed through the coordination interaction of Mn(II) and dpdo. The luminescent properties of the polymers were investigated in the solid state at room temperature.