Type Polyoxometalate Research Articles

Experimental investigation to check the relation of third order optical nonlinearities of Dawson polyoxometalate-porphyrin hybrids with excited state dynamics by using ultrafast life time decay technique

Two previously synthesized porphyrin-polyoxometalate hybrids as [(C4H9)4N)]5H[COHNC(CH2 O)3P2V3W15O59{C44H29N4}]·CH3CN and [(C4H9)4N]10H2[{COHNC(CH2O)3P2V3W15O59}2C44N4 H28]·CH3CN symbolized as [email protected] and [email protected] bearing one and two Wells-Dawson type polyoxometalates (POMs) respectively, have been considered regarding their fluorescence lifetime decay studies in comparison of third order non-linear optical (NLO) activities. The results showed that [email protected] possessing the superlative response for NLO properties and lifetime decay than [email protected] by exhibiting greater NLO properties (β = 2.90, γ = 12.91, χ3 = 2.56, Imχ (3) = 3.73) and shorter lifetime decay values (τ1 = 1.09 & τ2 = 4.22). Presenting quick intersystem crossing (ISC) development by shifting their energy from singlet to triplet excited-states.

Electrochemical Studies of LbL Films With Dawson Type Heteropolyanion Glassy Carbon Electrode Sensor Modified for Methyl Parathion Detection

Rapid methyl parathion detection was measured using a fabricated glassy carbon electrode (GCE) sensor designed using the layer-by-layer (LBL) method. Multilayer assemblies were developed on the glassy carbon electrode by alternating depositions of anions and cations in which a Dawson Type Polyoxometalate β-K6[(P2W18O62·H2O)]·14H2O (∼P2W18 POM) and polyethyleneimine (PEI) stabilized silver nanoparticles (∼PEI-AgNPs) acted as anions and cations, respectively. The redox behavior of P2W18 POM within LBL assembly was carried out via cyclic voltammetry. This LBL assembly was thoroughly characterized by UV-Visible, FT-IR, XRD, AFM, and SEM techniques. The fabricate GCE sensor was investigated for the electrocatalytic activity to detect methyl parathion. The results clearly showed that the fabricated GCE sensor was successfully synthesized. More interestingly, the current response for detecting methyl parathion was found to be less than 1 ppm, proving that this fabricated GCE sensor may exhibit potential applications in the detection of targeted pesticide.

A Lindqvist type hexamolybdate [Mo6O19]-modified graphene oxide hybrid catalyst: Highly efficient for the synthesis of benzimidazoles

In this work, a novel organic–inorganic hybrid catalyst ([Mo6O18] @GO-NH2) was synthesized by covalent attachment of Lindqvist type polyoxometalate [(C4H9)4N]2[Mo6O19] on the surface of graphene oxide (GO). To provide the hybrid catalyst, graphene oxide was covalently modified with an aminosilane, followed by treatment with a polyoxometalate complex. The resulting catalyst was identified by different analytical techniques TG, SEM, XRD, BET, EDX, FT-IR, and N2 adsorption–desorption. [Mo6O18] @GO-NH2 was used as an efficient catalyst for the preparation of various benzimidazoles. The result showed high activity, recoverability, reusability, and durability of the designed catalyst under applied conditions.

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.

A Novel Anderson-Evans Polyoxometalate-based Metal-organic Framework Composite for the Highly Selective Isolation and Purification of Cytochrome C from Porcine Heart

Anderson-Evans type polyoxometalate group (Na6[TeW6O24]·22 H2O, TeW6) was combined with porous metal-organic framework ZIF-8 by electrostatic interaction to obtain a novel Anderson-Evans polyoxometalate-based metal-organic framework composite, TeW6 @ZIF-8. FT-IR, Raman, XRD, TG, DSC, SEM, and TEM were used to characterize the composite. It was proved that the Anderson-Evans type polyoxometalate group TeW6 was successfully hybridized with metal-organic framework ZIF-8, and the composite possesses good stability. Based on the potential interaction between TeW6 and proteins and the coordination between imidazole groups in ZIF-8 and proteins with a porphyrin ring structure, the adsorption selectivity towards different proteins on the TeW6 @ZIF-8 composite was studied in this work. The experiment results showed that the TeW6 @ZIF-8 composite was selectively adsorbed to cytochrome C. At pH 11.0, the adsorption efficiency of 94.01% was obtained for processing 1.0 mL 100 μg mL-1 cytochrome C with 3.0 mg TeW6 @ZIF-8 composite. The adsorption behavior of cytochrome C fits well with the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 232.56 mg g-1. The retained cytochrome C could be readily recovered by 1% SDS (m/m), giving rise to a recovery of 65.6%. Circular dichroism spectra indicate no conformational change for cytochrome C after the adsorption and desorption processes, demonstrating the favorable biocompatibility of TeW6 @ZIF-8 composite. In applying practical samples, SDS-PAGE results showed that cytochrome C was successfully isolated and purified by TeW6 @ZIF-8 composite from porcine heart protein extract, which is further identified with LC-MS/MS. Thus, a new strategy for separating and purifying cytochrome C from the porcine heart using TeW6 @ZIF-8 composite as an adsorbent was established.

Promoting the effect of cationic substitution on thermal stability and redox properties of new synthesized Keggin type lacunary polyoxometalates (L-POMs) Ni2.5PMo11 M(H2O)O39 (M = Co, Fe, Cu, Zn)

Abstract New lacunary Keggin type polyoxometalate salts (Ni2.5PMo11 M(H2O)O39/M = Co, Fe, Cu, Zn), were synthesized using the inorganic condensation method. X-ray diffraction and infrared spectroscopy results showed that the Keggin structure of the salts was preserved. The thermal stability was checked by differential scanning calorimetry coupled with thermogravimetric analysis showing that the thermal resistance was significantly improved by the incorporation of the metals into polyoxometalates. Proton and molybdenum substitution respectively by nickel and cobalt, iron, copper and zinc metals induced a positive effect on the crystallographic configuration of the prepared salts allowing them a better thermal resistance (up to 580 °C). Cyclic voltammetry revealed an interesting electrochemical property of synthesized samples, especially for Ni2.5PMo11Zn(H2O)O39 sample in which the presence of zinc greatly boosted the redox behavior.

Zinc Substituted Keggin type Polyoxometalate as an effective Catalyst for the Oxidative Desulfurization of Dibenzothiophen by Hydrogen Peroxide as Oxidant

Zinc Substituted Keggin type Polyoxometalate as an effective Catalyst for the Oxidative Desulfurization of Dibenzothiophen by Hydrogen Peroxide as Oxidant

Wells-Dawson Type Polyoxometalate, [S2w18o62]4--Doped Poly(3,4-Ethylenedioxythiophene) Film: Voltammetric Behaviour and its Application to Selective Bromate Detection

Wells-Dawson Type Polyoxometalate, [S2w18o62]4--Doped Poly(3,4-Ethylenedioxythiophene) Film: Voltammetric Behaviour and its Application to Selective Bromate Detection

Ultrasensitive photochromic and Raman dual response to ethylenediamine gas through polyoxometalate–viologen crystalline hybrid

A new crystalline complex is successfully synthesized based on Dawson type polyoxometalate and amino substituted viologen. It exhibits ultrasensitive photochromic and Raman dual response to ethylenediamine gas.

Inhibition and self-inhibition phenomena in mixed solutions of Anderson type polyoxometalates

• Polyoxometalates are able to form barrier layers. • Co-adsorption of two polyoxometalates affects barrier properties. • Self-inhibition of central ion reduction is affected by co-adsorption. Adsorption of Anderson-type polyoxometalates on mercury is addressed by classical polarography. The outersphere perbromate reduction is considered to probe the barrier properties of polyoxometalate adlayers. A mutual effect of polyanions with Co(II), Co(III), and Ni(II) as central atoms is shown to affect both their adsorption and the inhibition of perbromate reduction, as well as the self-inhibition of Co(III) reduction. The difference in adlayer-induced inhibition effects for individual polyanions and their mixtures is interpreted on the basis of molecular modeling with account for co-adsorption with cations. Our observations demonstrate that a wide variety of barrier properties can be implemented due to orientation effects and adsorption behavior controlled by the electrode charge.

Synthesis of polyoxometalate based copper-amino-triazole inorganic-organic hybrid materials and related chemistry

We have described in this article a copper(II) compound [Cu(C9H7N4O)2]n (1) and two polyoxometalate (POM)-based inorganic–organic hybrid materials [(C2H6N5)2(C9H9N4O)2][Cu(H2O)2(C9H8N4O)2(PW12O40)2] (2) and [Cu(C9H8N4O)6][HPW12O40] (3). Compound 1 is coordination polymer based on the coordination complex [Cu(C9H7N4O)2], where the ligand C9H7N4O is 4-(salicylideneamino)-1,2,4-triazole (Hsaltrz). Compounds 2 and 3 additionally include the phospho-tungstate type polyoxometalate (POM). Compound 2 is unique in the sense that it is isolated with the 1,4-diamino-4H-1,2,4-triazolium cation [C2H6N5]2+, which is formed in-situ from Hsaltrz during the synthesis of compound 2. Notably, the in-situ formed molecule, 1,4-diamino-4H-1,2,4-triazolium cation, is known to be a high-energy performing molecule. The title compounds have been characterized by routine spectral analysis including their unambiguous characterization by single crystal X-ray crystallography. Density functional theory (DFT) calculations were performed on these three compounds using the Gaussian 09 W program to understand the system better.

Well-Dawson type polyoxometalates of 3d series and their industrial use as eco-friendly and green catalysts in organic reactions

Well-Dawson type polyoxometalates of 3d series and their industrial use as eco-friendly and green catalysts in organic reactions

Polyoxometalate intercalated La-doped NiFe-LDH for efficient removal of tetracycline via peroxymonosulfate activation

• La-doped NiFe-LDH containing Keggin type polyoxometalate interlayer were synthesized. • The NiFeLa{HPW}-LDH exhibited better catalytic performance than NiFeLa-LDH. • The intercalated HPW played a vital role in electron transfer. • SO 4 − and OH were the main radicals in catalytic degradation of tetracycline. • The formation of the complex and redox cycle were responsible for the catalysis. In this work, a series of La-doped NiFe-layered double hydroxides containing a novel Keggin type polyoxometalate interlayer (NiFeLa{HPW}-LDH) were synthesized and initially applied as heterogeneous catalyst for peroxymonosulfate (PMS) activation. Characterizations indicated that polyoxometalate anions were successfully intercalated in the layers of NiFeLa-LDH. Experiment results showed that NiFeLa{HPW}-LDH exhibited better catalytic performance than the counterpart precursor. The influences of various experimental parameters, such as pH value, initial TC concentration, HPW intercalation content, catalyst loading and peroxymonosulfate concentration were investigated in detail. Quenching experiments and the results of electron paramagnetic resonance (EPR) demonstrated the SO 4 − and HO were the dominant reactive radicals engaging in the degradation process. Furthermore, the formation of a complex of Ni(II)/Fe(II)/La(III)−(HO)OSO 3 − and the succeeding redox cycle of Ni(II)/Ni(III)/Ni(II), Fe(II)/Fe(III)/Fe(II), La(III)/La(IV)/La(III) were responsible for the generation of active radicals via activating PMS. Meanwhile, it's worth noting that the intercalated HPW also played a vital role in electron transfer.

Immobilization of Polyoxometalate onto Modified Magnetic Nanoparticles: A New Catalyst for the Synthesis of Dihydropyranopyrazole Derivatives

AbstractA new nanocatalyst Fe3O4@carbon@polyoxometalate (Fe@C@Mo6O18) consisting of a cluster of Fe3O4nanoparticles as core, a carbon layer as inner shell, and a Lindqvist type polyoxometalate as the outer shell was prepared. The prepared nanocatalyst structure was characterized by energy dispersive X‐ray (EDX), scanning electron microscopy (SEM), vibration sample magnetometer (VSM), thermogravimetric analysis (TGA), and Fourier transform infrared (FT‐IR) spectroscopy techniques and their catalytic activity was evaluated for the synthesis of dihydropyranopyrazole derivatives. The results were excellent regarding the high yield of the products and short reaction time. The new nanocatalyst showed good recoverability with a significant loss of activity and selectivity within successive runs. Most importantly, these materials can be easily recovered by simple magnetic separation.

Theoretical comparative survey on the structure and electronic properties of first row transition metal substituted Keggin type polyoxometalates

In the present study, molecular geometry, electronic structure, first row transition metal-polyoxometalate interactions, transition metal-H2O bonding, and simulated infrared (IR) spectrum of H2O ligated/unligated transition metal substituted Keggin type polyoxometalates ([PW11O39(MII/MIIOH2)]5-, MII ​= ​Cr, Mn, Fe, Co, Ni, Cu and Zn) have been studied through Density Functional Theory (DFT) calculations. From the results, it has been predicted that the interaction of H2O ligand with MII leads to a stable [PW11O39(MII-H2O)]5- complex, without spin crossing during water attachment. The calculations have also revealed that interaction of H2O ligand with [PW11O39(MII)]5- could be discussed in two different classes: when MII is Cr, Mn and Fe, the H2O molecule interacts directly to MII from O side, while for MII ​= ​Co, Ni, Cu and Zn, the H-bond interaction between H2O and O atoms around the M, leads to the stabilization of POM-H2O system. Moreover, it has been predicted that the binding properties of H2O strikingly depends on axial 3dz2 orbital of MII. In this regard, it has been exhibited that the affinity of H2O for MII in [PW11O39(MII)]5- with a filled 3dz2 orbital, is strongly reduced as measured by increasing in calculated MII-ligand distance. Also, strong contributions of MII 3d as well as the 2p orbitals of five oxygen donor atoms in polyoxometalate cluster results in the bonding interaction between MII and lacunary Keggin polyoxometalate. The DFT-derived IR spectra showed displacement and splitting in four previously known vibrational bands of Keggin-type polyoxometalate, α-[PW12O40]3-, owing to transition metal substitution and H2O ligation.

Folic acid bonded (Bu4N)5H4[P2W15V3O62] as a smart hybrid compound for cancer cells targeting

A new hybrid compound was synthesized via the covalent grafting of vanadium-substituted Wells-Dawson type polyoxometalate (Bu4N)5H4[P2W15V3O62] to folic acid. The cytotoxic effect of the resulted bioactive hybrid compound was investigated on cervical (HeLa) and human breast (MCF-7) cancer cells. Interestingly this smart hybrid compound could knockdown cancer cells (IC50 about 19 and 75 µgmL−1 for HeLa and MCF-7 respectively), while the normal cells, as a folate receptor (FR) negative cell, remained nearly untreated (IC50 about 317 µgmL−1). Higher cytotoxicity of this hybrid polyoxometalate on HeLa than MCF-7 cells could be attributed to the higher expression of folic acid on HeLa. The IC50 for (Bu4N)5H4[P2W15V3O62] on healthy cells (about 84 µgmL−1) showed four times improvement in the polyoxometalate biocompatibility by incorporation of folic acid. In comparison to methotrexate (as a positive control), this smart polyoxometalate-folic acid hybrid compound has a high potential for developing a significant and selective therapeutic effect against FR-positive cancer cells.

Exploration on χ-Anderson type Polyoxometalates based hybrids towards photovoltaic response in solar cell

Two polymerized χ-Anderson type Polyoxometalates based hybrids [N(C4H9)4]3[C(CH2O)3Zn Mo6O18C(CH2O)3CH2OCH2] and [N(C4H9)4]3[C(CH2O)3ZnMo6O18C(CH2O)3(CH2OCH2)2C (CH2OH)2] named as (TBA)3[CA-Di@POM] and (TBA)3[CA-Tri@POM ], respectively have been prepared and different techniques such as FTIR, NMR(1H, 13C) and mass spectrometry were used to characterize these hybrids. Moreover, their photovoltaic performance in solar cell have been explored through current–voltage (I-V) curve. Different photochemical parameters such as short circuit current (ISC), open circuit voltage (VOC), fill factor (FF) and efficiency (η) were measured from I to V curve and compared with literature. It is indicated from these results that there is notable enhancement in the efficiency of (TBA)3[CA-Di@POM] and (TBA)3[CA-Tri@POM] films in solar cell which were calculated as 0.58% and 1.25% respectively.

A comparative catalytic study using different metal ions by incorporating functionalized metallosalen into the lacunary position of Keggin polyoxometalate

A series of new hybrids, POM (M-Salen@POM) were synthesized by successfully inserting metallosalen compounds (where M ​= ​Co, Cu, Fe and Ru) into the lacunary position of Keggin type polyoxometalate, K8SiW11O39 (POM). The hybrids were characterized by FT-IR, powder XRD, diffuse reflectance UV–Vis, energy dispersive X-Ray and inductively coupled plasma atomic emission spectroscopy (ICP) techniques. The hybrids with different metal centers were comparatively studied for their catalytic activity in the oxidation of cycloalkanes, cycloalcohols and alkyl aromatic using a green oxidant, hydrogen peroxide. The products obtained during catalysis were estimated by gas chromatography(GC) and mass spectroscopy(MS). Catalytically synthesized products are of high industrial importance.

Modification of Cu/Cr Layered Double Hydroxide by Keggin Type Polyoxometalate as Adsorbent of Malachite Green from Aqueous Solution

Modification of Cu/Cr layered double hydroxides (LDHs) has been conducted by intercalation using Keggin type polyoxometalate [a-SiW12O40]4- to form CuCr-[a-SiW12O40]. The materials were analyzed by XRD, FTIR, and surface area analyses. Furthermore, materials were used as selectivity adsorbents of cationic dyes such as malachite green, rhodamine-B and methylene blue. The malachite green is more selective than others from an aqueous solution. The adsorption of malachite green showed that the adsorption capacity of CuCr-[a-SiW12O40] was higher than pristine LDHs. The adsorption process was followed pseudo second order kinetic model and Langmuir isotherm adsorption. The Qmax value of CuCr-[a-SiW12O40] reached 55.322 mg/g at 323 K after 100 minutes adsorption time. Thermodynamic parameters such as ΔG, ΔH and ΔS confirm that the adsorption process was endothermic, spontaneous, and more favorable at high temperatures. The intercalated material was higher structural stability toward reusability adsorbent than pristine LDHs.

In Situ Electrochemical Production of Metal‐organic Hybrid Composite Film from Nickel Containing Polyoxometalate and 3,4‐Ethylenedioxy‐thiophene for Sensor Application

AbstractIn situ electrochemical synthesis of an organic‐inorganic hybrid material composed of poly(3,4‐ethylenedioxythiophene) (PEDOT) and nickel‐based Keggin type polyoxometalate, K7[NiIIINiII(H2O)W11O39].15H2O(NiPOM), has been proposed here. The remarkable optical and electrical properties of the PEDOT and the unique redox properties of NiPOM have synergistically combined to make the hybrid structure highly desired multi‐functional materials for a myriad of applications. The driving force for the formation of hybrid structure is thought to be electrostatic interactions between POM anions and cationic polaron/bipolaron structures that in the PEDOT. PEDOT/NiPOM based hybrid composite modified graphite electrode has been used for non‐enzymatic glucose sensor platform as a sample of applications. Furthermore, PEDOT/NiPOM based sensor platform was successfully utilized for detection of glucose content with the lowest detection limit in real samples like honey and milk. These results suggest that PEDOT/NiPOM metal‐organic hybrid composite could be utilized as multi‐functional material for a myriad of applications.