Diphosphoryl-functionalized Polyoxometalates: Structurally and Electronically Tunable Hybrid Molecular Materials

Herein, we report the synthesis and characterization of a new class of hybrid Wells-Dawson polyoxometalate (POM) containing a diphosphoryl group (P2 O6 X) of the general formula [P2 W17 O57 (P2 O6 X)]6- (X=O, NH, or CR1 R2 ). Modifying the bridging unit X was found to impact the redox potentials of the POM. The ease with which a range of α-functionalized diphosphonic acids (X=CR1 R2 ) can be prepared provides possibilities to access diverse functionalized hybrid POMs. Compared to existing phosphonate hybrid Wells-Dawson POMs, diphosphoryl-substituted POMs offer a wider tunable redox window and enhanced hydrolytic stability. This study provides a basis for the rational design and synthesis of next-generation hybrid Wells-Dawson POMs.

A POM-based copper-coordination polymer crystal material for phenolic compound degradation by immobilizing horseradish peroxidase

A new polyoxometalate (POM)-based organic-inorganic hybrid Cu-coordination polymer, namely {((Cu(bipy))2(μ-PhPO3)2Cu(bipy))2H(PCuW11O39)·3H2O}n (denoted as compound 1, bipy = 2,2'-bipyridine, PhPO3 = phenylphosphonate), was self-assembled hydrothermally. Single-crystal X-ray diffraction (SC-XRD) analysis shows that two unique types of 1D chains are present in compound 1, i.e. Cu(II)-organophosphine and organonitrogen complex cation ([((Cu(bipy))2(μ-PhPO3)2Cu(bipy))2]4+) chains and Cu-monosubstituted Keggin-type polyoxoanion ([PCuW11O39]5-) chains, forming a hetero-POM. Crystalline compound 1 as a new enzyme immobilization support exhibited a high horseradish peroxidase (HRP) loading capacity (268 mg g-1). The powder X-ray diffraction (PXRD), FTIR, zeta potential, confocal laser scanning microscopy (CLSM) and circular dichroism (CD) results show that HRP is only immobilized on the surface of compound 1 through simple physical adsorption without a secondary structure change. This POM-immobilized enzyme (HRP/1) was first used for degradation of pollutants in wastewater, and it showed a high degradation efficiency and TOC removal efficiency for phenol, 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) within 30 min reaction time. Moreover, HRP/1 exhibited better operational and storage stabilities and reusability compared with free HRP. This work suggests that POMs can be used as new supports for enzyme immobilization and POM-immobilized enzymes may be used as a new kind of biocatalyst for degradation of phenolic pollutants.

A silver-substituted phosphomolybdate prevents the growth of bacteria without affecting the balance of reactive oxygen species

A novel 2D nanoscale silver-substituted Strandberg-type phosphomolybdate shows good inhibitory effect on the growth of Escherichia coli.

A CsCl-type inorganic cluster-based high-symmetry crystal built from {Mo4.55V7.45PO40}10.45- with a high ratio of vanadium to molybdenum and {(H2O)0.3@K6(H2O)12}6+ clusters exhibiting proton conduction below the freezing point of water

As a class of anionic oxoclusters of early transition metals in their highest oxidation states, polyoxometalates (POMs) show considerable structural versatility and unique chemical and physical properties, making them promising multifunctional materials. In this study, a Keggin-type POM has been achieved, with a formula of [(H2O)0.3@K6(H2O)12]H4.45[PV7.45Mo4.55O40]·11H2O (1), and its microcrystals and nanocrystals have been obtained, respectively. This POM was characterized by elemental analysis for C, H and N, ICP-MS, TG, PXRD, SEM, X-band EPR and XPS techniques. Single crystal X-ray diffraction analysis demonstrated that 1 shows a rare extended structure with a high-connected three-dimensional (3D) all inorganic network of a Keggin-type POM, built from {Mo4.55V7.45PO40}10.45- polyoxoanions and {(H2O)0.3@K6(H2O)12}6+ clusters with CsCl-type crystal structure. In addition, to the best of our knowledge, 1 shows the highest ratio of vanadium to molybdenum among Keggin-type POMs reported thus far. Most interestingly, 1 exhibits intrinsic proton conduction below the freezing point of water, with a proton conductivity of 6.90 × 10-7 S cm-1 at 249 K and further reaching 3.36 × 10-6 S cm-1 at 272 K and Ea = 0.44 eV at 249-272 K.

Phosphonate Decomposition-Induced Polyoxomolybdate Dumbbell-Type Cluster Formation: Structural Analysis, Proton Conduction, and Catalytic Sulfoxide Reduction

The reaction of MoO₄^2- with a number of phosphonic acids [bis(phosphonomethyl)glycine, R,S-hydroxyphosphonoacetic acid, 1-hydroxyethane-1,1-diphosphonic acid, phenylphosphonic acid, aminotris(methylene phosphonic acid), and 1,2-ethylenediphosphonic acid] under oxidizing (H₂O₂) hydrothermal conditions at low pH leads to rupture of the P-C bond, release of orthophosphate ions, and generation of the octanuclear, phosphate-bridged, polyoxometalate molybdenum cluster (NH₄)₅[Mo₈(OH)₂O₂₄(μ₈-PO₄)](H₂O)₂ (POMPhos). This cluster has been fully characterized and its structure determined. It was studied as a proton conductor, giving moderate values of σ = 2.13 × 10^-5 S·cm^-1 (25 °C) and 1.17 × 10^-4 S·cm^-1 (80 °C) at 95% relative humidity, with E_a = 0.27 eV. The POMPhos cluster was then thermally treated at 310 °C, yielding (NH₄)_2.6(H₃O)_0.4(PO₄Mo₁₂O₃₆) together with an amorphous impurity containing phosphate and molybdenum oxide. This product was also studied for its proton conductivity properties, giving rise to an impressively high value of σ = 2.43 × 10^-3 S·cm^-1 (25 °C) and 6.67 × 10^-3 S·cm^-1 (80 °C) at 95% relative humidity, 2 orders of magnitude higher than those corresponding to the "as-synthesized" solid. The utilization of POMPhos in catalytic reduction of different sulfoxides was also evaluated. POMPhos acts as an efficient homogeneous catalyst for the reduction of diphenyl sulfoxide to diphenyl sulfide, as a model reaction. Pinacol was used as a low-cost, environmentally friendly, and highly efficient reducing agent. The effects of different reaction parameters were investigated, namely the type of solvent and reducing agent, presence of acid promoter, reaction time and temperature, loading of catalyst and pinacol, allowing to achieve up to 84-99% yields of sulfide products under optimized conditions. Substrate scope was tested on the examples of diaryl, alkylaryl, dibenzyl, and dialkyl sulfoxides and excellent product yields were obtained.

A binuclear copper-substituted phosphomolybdate with reactive oxygen species catalytic ability and antimicrobial activity

A magnetic binuclear Cu-substituted Strandberg POM can produce ROS and inhibit the growth of E. coli.

Synthesis and structural characterization of a dumbbell-like phenylphosphonate-stabilized Ti7-oxide cluster

In recent years, crystalline polyoxotitanium clusters (PTCs) have attracted increasing attention as a new kind of promising crystalline material. In this work, a PTC stabilized by phenylphosphonate ligands, i.e. hexa-μ-isopropanolato-hexaisopropanolatodi-μ₃-oxido-hexa-μ₃-phenylphosphonato-heptatitanium tetrahydrate, [Ti₇(μ₃-O)₂(O₃P-Phen)₆(OⁱPr)₁₂]·4H₂O [PTC-54; H₂O₃P-Phen is phenylphosphonic acid, C₆H₅PO(OH)₂, and HOⁱPr is isopropanol, C₃H₇OH], was obtained successfully through a facile one-step solvothermal reaction. The dumbbell-like core structure of PTC-54 can be described as two trinuclear {Ti₃(μ₃-O)} building units combined together by six phenylphosphonate ligands and one additional Ti atom, giving rise to a Ti₇ cluster. Adjacent molecules of PTC-54 are further connected through π-π interactions between the phenyl groups to form a supramolecular one-dimensional chain.

All-Inorganic Ionic Porous Material Based on Giant Spherical Polyoxometalates Containing Core-Shell K6 @K36 -Water Cage

This work demonstrates that the use of high-negative and high-symmetry lacunary polyoxometalates (POMs) for the clustering of alkali metal ions is a feasible strategy not only for the formation of rare high-nuclearity alkali-metal clusters but also for the construction of new-type all-inorganic ionic porous materials. By the strategy, an unprecedented high-nuclearity K-H₂ O cluster {K₄₂ (H₂ O)₆₀ } with core-shell K₆ @K₃₆ configuration is stabilized by 8 C_3v -symmetry trivacant POMs [GeW₉ O₃₄ ]^10- , forming a novel giant ionic alkali-metal-POM composite cluster {K₄₂ Ge₈ W₇₂ O₂₇₂ (H₂ O)₆₀ } with more than 100 metal centers. The incorporated 42-nuclearity K-H₂ O cluster {K₄₂ (H₂ O)₆₀ } exhibits the highest-nuclearity alkali-metal-water cluster known to date in POM chemistry. Further, the giant {K₄₂ Ge₈ W₇₂ O₂₇₂ (H₂ O)₆₀ } clusters can be linked by another kind of alkali metal ions Na⁺ to generate a fascinating three-dimensional all-inorganic ionic porous framework with high chemical stability, proton conductivity, and water vapor adsorption.

Three new Strandberg-type phenylphosphomolybdate supports for immobilizing horseradish peroxidase and their catalytic oxidation performances

Three new Strandberg-type polyoxometalate TM-(PhP)2Mo5 supports for immobilizing HRP showed high adsorption capacity and good catalytic oxidation activity.