Assembly of Organic–Inorganic Hybrid Supramolecular Materials Based on Basketlike {M⊂P6Mo18O73} (M = Ca, Sr, Ba) Cage and Transition-Metal Complex

Porous {P6Mo18O73}-type Poly(oxometalate) Metal-Organic Frameworks for Improved Pseudocapacitance and Electrochemical Sensing Performance

{P₆Mo₁₈} poly(oxometalate) (POM) clusters have huge steric hindrance and limited active oxygen atoms, which make them difficult to combine with metal-organic units to form three-dimensional (3D) porous structures. Therefore, functionalization of such POMs has always been a bottleneck that is difficult to break through. In this study, {P₆Mo₁₈} POM was successfully grafted on a lock-like metal-organic chain to generate a multiporous coordination polymer, [{Na(H₂O)(H₂btb)}{Cu₄^I(H₂O)(pz)₅Cl}{H₂Sr⊂P₆Mo₂^VMo₁₆^VIO₇₃}]·3H₂O (1) (pz = pyrazine; btb = 1,4-bis(1,2,4-triazole) butane). Meanwhile, a zero-dimensional (0-D) control compound with only btb ligands as counterions, (H₄btb)[H₄Sr⊂P₆Mo₂^VMo₁₆^VIO₇₃]·3H₂O (2), was also obtained via a hydrothermal reaction. Compound 1 represents the first basket-type 3D poly(oxometalate) metal-organic framework (POMOF) assembly, which possesses interpenetrating pores and complex topology. 1-GO-CPE displays improved supercapacitor (SC) performance (the specific capacitance of 929.4 F g^-1 at a current density of 3 A g^-1 with 94.1% of cycle efficiency after 5000 cycles) compared with 2-GO-CPE and most reported POMOF electrode materials, which may be due to the outstanding redox capability of basket-POM, introduction of metal-organic chains, intersecting pores, and excellent conductivity of graphene. An asymmetric SC device with 1-GO-CPE as the negative electrode exhibits an energy density of 29.7 Wh kg^-1 with a power density of 3148.2 W kg^-1 and long-lasting cycling life. In addition, 1-GO-GCE as an electrochemical sensor responds to dopamine (DA) at a voltage of 0.40 V and shows lower detection limits (0.19 μM (signal-to-noise ratio (SNR) = 3)), higher selectivity, and good reproducibility in the linear range of 0.56 μM to 0.24 mM. The ability to accurately detect the content of DA in biological samples further proves the feasibility of the sensor in practical applications.

Self-assembly of a novel multicomponent polyoxometalate-based tetrahedral supercluster with high catalytic activity for thioether oxidation

A novel tetrahedral supercluster [(P2Co2MoV4O8)2(P2MoV2O8)4(Pb⊂P6Co2MoV2MoVI14O73)4]12− with multiple components has been successfully synthesized, which exhibits high catalytic activity for the oxidation of thioether.

Ammonium phosphomolybdate: a material for dielectric crossover and resistive switching performance

The yellow ammonium phosphomolybdate [(NH₄)₃PMo₁₂O₄₀] (YAPM) is a robust and elegant compound that has found innumerable field applications. Herein, we have shown that this inorganic polymer serves as a novel dielectric material and a compound for memory device fabrication. It displays changeable dielectric performance and ac conductivity under UV (∼365 nm) irradiation. Drastic lowering of the dielectric constant (ε') was observed with the increase in dielectric loss factor, which was ascertained due to electron accumulation under UV exposure producing green APM (GAPM). The contributions of the Maxwell-Wagner polarization and the dipolar relaxation are correlated with the charge transfer and dielectric contribution of the material. Interestingly, the pressure-induced reduction of Mo(vi) to Mo(v) is reported for the first time and is similar to UV-exposed mixed-valence GAPM, which was corroborated by EPR spectra. In the ac signal, the crossover from quantum mechanical tunneling to hopping conduction is an adequate explanation for YAPM under UV irradiation. The fabricated device Au‖YAPM‖Au on a flexible paper substrate shows a resistive memory behavior that is modeled as a Schottky-type emission (SE) and Poole-Frenkel (PF) carrier transport for the OFF and ON states, respectively. The device exhibited a constant ON-OFF current ratio of 2 × 10² for YAPM. The OFF state endurance of the device (with 3 V pulses having 1 s time-period) under UV showed a steady increment current strength with time. After 100 s of UV exposure, the Au‖YAPM‖Au device became Au‖GAPM‖Au, and the conductivity completely shifted to a stable ON-state (at 300 s).

Crystal structure of a heterometallic coordination polymer: catena-poly[[[tetra-aqua-cobalt(II)]-μ-pyridine-2,6-di-carboxyl-ato-calcium(II)-μ-pyridine-2,6-di-carboxyl-ato] dihydrate]

In the crystal of the title polymeric complex, {[CoCa(C7H3NO4)2(H2O)4]·2H2O} n (1), the CoII ion is N,O,O'-chelated by two pyridine-2,6-di-carboxyl-ate anions in a distorted N2O4 octa-hedral geometry, and two carboxyl-ate O atoms of pyridine-2,6-di-carboxyl-ate anions bridge tetra-aqua-calcium(II) units to form polymeric chains propagating along the b-axis direction. In the crystal, O-H⋯O and C-H⋯O hydrogen bonds, and offset π-π stacking inter-actions [inter-centroid distances = 3.551 (1) and 3.746 (1) Å] involving inversion-related pyridine rings link the polymeric chains and lattice water mol-ecules to form a supra-molecular three-dimensional framework.

Three new compounds based on similar molybdenum–vanadium clusters and several types of copper complexes

A series of new organic–inorganic hybrid compounds based on Mo–V clusters and several types of transition metal complexes have been synthesized and characterized.

Long rigid ligand induced basket-type phosphomolybdate photo-/electro-catalytic materials

Two long rigid ligands are introduced into {P₆Mo₁₈O₇₃} systems, leading to two unique supramolecular hybrid assemblies, which show highly efficient catalytic activity for the degradation of refractory dye AP under UV light and bifunctional electrocatalytic behavior for the oxidation of dopamine (DA) and reduction of H₂O₂.

Effective photocatalytic and bifunctional electrocatalytic materials based on Keggin arsenomolybdates and different transition metal capped assemblies

V, Co, and Cu were introduced into {AsMo₁₂} system to build three Keggin derivatives with different caps, which show excellent photocatalytic activity and bifunctional electrocatalytic behavior.

Evans–Showell-type polyoxometalate constructing novel 3D inorganic architectures with alkaline earth metal linkers: syntheses, structures and catalytic properties

Two 3D frameworks and two 2D networks with an excellent catalytic effect of cyanosilylation were successfully obtained, originating from Evans–Showell-type polyoxoanions [Co₂Mo₁₀H₄O₃₈]⁶⁻ and alkaline earth metal cations (Sr²⁺, Ba²⁺).

A novel polyoxometalate-based hybrid containing a 2D [CoMo8O26]∞ structure as the anode for lithium-ion batteries

A novel polyoxometalate-based anode material was fabricated and showed high initial reversible specific capacity and stable reversible capacity, indicating a prospective class of anode materials for LIBs.

The basket-type dimer layers based on tetra-electron reduced heteropoly blue directed by copper/nickel and strontium linkers

Two basket-type dimer layers have been prepared, which exhibit highly efficient catalytic ability for the degradation of typical dyes and bifunctional electrocatalytic behaviors.

pH-Controlled assembly of two novel Dawson-sandwiched clusters involving the in situ reorganization of trivacant α-[P2W15O56](12-) into divacant α-[P2W16O57](8.)

Modified classical trivacant Wells-Dawson α-[P2W15O56](12-) and the assembly of related sandwiched transition metal clusters are of interest, but surprisingly few reports of these materials exist because of the sensitivity of α-[P2W15O56](12-) to the assembly environment. Herein, we describe the pH-controlled assembly of two novel Dawson-sandwiched clusters, (H2bpz)6[Co2(P2W16O57)2]·22H2O (1, bpz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole) and (H2bpz)6[Co3H2(P2W16O57)(P2W15O56)(H2O)]·12H2O (2), involving the in situ transformation of α-[P2W15O56](12-). Both clusters were characterized by X-ray single-crystal diffraction, FT-IR spectroscopy, UV-Visible spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and elemental analyses. X-ray crystallography showed that both heteropolytungstates become divacant α-[P2W16O57](8-) and symmetrically encapsulate two edge-shared CoO6 octahedra in the interior in 1, while only one divacant α-[P2W16O57](8-) is observed in 2, which combined with another trivacant α-[P2W15O56](12-) to asymmetrically clamp three edge-shared CoO6 octahedra. The α-[P2W16O57](8-) heteropolytungstate should be generated in situ from α-[P2W15O56](12-)via self-decomposition equilibria in solution. Their electrochemical behaviors reveal characteristic multi-electron redox processes related to W(VI) centers. The electrocatalytic reduction performances toward nitrite, hydrogen peroxide, chlorate, bromate and iodate were fully measured and discussed; among these species, both clusters exhibit the best electrocatalytic activity towards the reduction of bromate. Magnetic measurements indicate weak ferromagnetic exchange interactions between Co atoms sandwiched by vacant polyoxometalates.

Assembly of a basket-like {Sr ⊂ P6Mo18O73} cage from 0D dimmer to 2D network and its photo-/electro-catalytic properties

Five semiconductor materials based on basket-like POM have been hydrothermally synthesized, which show high-efficient degradation ability for organic dyes RhB, MB, and AP in short time and bifunctional electrocatalytic behavior for oxidation of AA and reduction of NO₂⁻.

High-efficiency photo- and electro-catalytic material based on a basket-like {Sr⊂P6Mo18O73} cage

The first 8-connected 2D layer based on basket-liked {Sr⊂P₆Mo₁₈O₇₃} cage was prepared, which exhibits high-efficient photodegradation ability for MB, RhB, and AP under visible and UV light, as well as bifunctional electrocatalytic behavior.

The highest connected pure inorganic 3D framework assembled by {P4Mo6} cluster and alkali metal potassium

Potassium cation is introduced into the {(P₄Mo₆} systems, leading to 18-connected assemblies, which represents the highest connection of the POMs and shows bifunctional electrocatalytic activities and excellent photocatalytic activities.