Cavity-Directed Synthesis of Labile Polyoxometalates for Catalysis in Confined Spaces

The artificial microenvironments inside coordination cages have gained significant attention for performing enzyme-like catalytic reactions by facilitating the formation of labile and complex molecules through a "ship-in-a-bottle" approach. Despite many fascinating examples, this approach remains scarcely explored in the context of synthesizing metallic clusters such as polyoxometalates (POMs). The development of innovative approaches to control and influence the speciation of POMs in aqueous solutions would greatly advance their applicability and could ultimately lead to the formation of elusive clusters that cannot be synthesized by using traditional methods. In this study, we employ host-guest stabilization within a coordination cage to enable a novel cavity-directed synthesis of labile POMs in aqueous solutions under mild conditions. The elusive Lindqvist [M6O19]2- (M=Mo or W) POMs were successfully synthesized at room temperature via the condensation of molybdate or tungstate building blocks within the confined cavity of a robust and water-soluble Pt6L4(NO3)12 coordination cage. Importantly, the encapsulation of these POMs enhances their stability in water, rendering them efficient catalysts for environmentally friendly and selective sulfoxidation reactions using H2O2 as a green oxidant in a pure aqueous medium. The approach developed in this paper offers a means to synthesize and stabilize the otherwise unstable metal-oxo clusters in water, which can broaden the scope of their applications.

Polyoxometalate/s-triazine hybrid heterostructures with ultrafast photochromic properties

As an emerging class of hybrid complexes, donor-acceptor (D-A) hybrid heterostructures, which combine the advantages of both organic and inorganic photoactive components, provide excellent platforms for the fabrication of photochromic materials with enhanced photo-responsive performances. Herein, four novel hybrid heterostructures, namely H3TPT·(PW12O40)·2NMP (1), (H1.5TPT)2·(PW12O40) (2), (H3TPT)2·(SiW12O40)·2Cl·2MeCN (3), and H3TPT·(HPMo12O40)·Cl·3NMP (4) (TPT is tri(4-pyridyl)-s-triazine, NMP is N-methylpyrrolidone), have been synthesized and characterized. Benefitting from the strong interactions (anion-π interactions) and matching electron energy levels between the donors and acceptors, some of them exhibited ultrafast photochromic behaviour even up to 1 second. Furthermore, based on experimental and theoretical calculations, the plausible PIET process and structure-activity relationship have been discussed in detail.

Rapid Oxidative Detoxification of Mustard Simulant by the Multisite Synergistic Catalytic Action of {PMoVI11MoVO40CuI8} Units

Under hydrothermal and solvent-thermal conditions, we synthesized two novel polyoxometalate (POM)-based hybrids: [CuI4(Pz)2(H2O)8(PMoVI11MoVO40)]·3.5H2O (1, Pz = pyrazine) and [(C2H8N)5(HPMoVI9MoV3O40)]·DMF·4H2O (2). Single-crystal X-ray diffraction indicates that compound 1 is a three-dimensional structure consisting of Cu (I), {PMo12} anions, Pz, and water, where Cu (I) can be considered as Lewis acid sites. Furthermore, both compounds 1 and 2 possess favorable catalysis activity in catalyzing the conversion of chemical warfare agent simulant 2-chloroethylethyl sulfide (CEES) to nontoxic production of 2-chloroethylethyl sulfoxide (CEESO) under ambient temperature. Significantly, 1 could realize 98% conversion and 100% selectivity of CEES owing to the multisite synergy in the {PMoVI11MoVO40CuI8} units in which the tricoordinated Cu (I) could interact with S and O atoms from CEES and H2O2, respectively. This interaction not only decreases the distance of CEES from peroxomolybdenum species formed by H2O2 but also activates CEES.

Two porous Ni-MOFs based on 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine showing solvent determined structures and distinctive sorption properties toward CO2 and alkanes

By regulating the solvent used for synthesis, two porous Ni-MOFs, namely {[Ni3(BTC)2(TPT)2/3(H2O)4.08(MeOH)0.92]·2DMF·0.5H2O·0.5MeOH}n (1) and {[Ni3(BTC)2(TPT)2(H2O)6]·6DMF}n (2) (H3BTC = 1,3,5-benzenetricarboxylic acid, TPT = 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine, DMF = N,N-dimethylformamide, and MeOH = methanol) were obtained. Compound 1 reveals a rigid 3D framework, while compound 2 shows a flexible 3-fold interpenetrated framework. Compound 1 exhibits a selective adsorption of CO2 due to the sieving effect of the rigid framework containing two types of cages with small apertures. Noteworthily, the flexible compound 2 displays an obviously guest-induced structural transformation. The desolvated compound 2 reveals a much higher capacity toward CO2 and n-C4H10 than those of N2 CH4, C2H6 and C3H8.

Photochromism of supramolecular assemblies based on benzenecarboxylate donors and viologen acceptors

Similar viologen acceptors, a regular change in donor moieties and photochromism provide an ideal model for elucidating D–A matching rules.

Effect of counter cations on the photochromic behaviors of three Zn–viologen complexes

Similar viologen cations, regular change in acceptor moieties and photochromism provide an ideal model for elucidating D–A matching rules.

Crystal structures of hybrid completely reduced phosphomolybdates and catalytic performance applied as molecular catalysts for the reduction of chromium(VI)

The exploration of highly efficient and low-cost catalysts for the treatment of hexavalent chromium Cr^VI in environmental remediation is currently one of the most challenging topics. Here, three phosphomolybdate hybrid compounds have been successfully isolated by the hydrothermal method and been applied as supramolecular catalysts for the reduction of Cr^VI. Single-crystal X-ray diffraction revealed their formulae as (H₂bpp)₂[Fe(H₂O)][Sr(H₂O)₄]₂{Fe[Mo₆O₁₂(OH)₃(H₂PO₄)(HPO₄)(PO₄)₂]₂}·5H₂O (1), (H₂bpp)₂[Na(H₂O)(OC₂H₅)][Fe(H₂O)₂][Ca(H₂O)₂]₂{Fe[Mo₆O₁₂(OH)₃(H₂PO₄)(HPO₄)(PO₄)₂]₂}·4H₂O (2) and (H₂bpe)₃{Fe[Mo₆O₁₂(OH)₃(HPO₄)₃(H₂PO₄)]₂}·8H₂O (3) [bpp is 1,3-bis(pyridin-4-yl)propane (C₁₃H₁₄N₂) and bpe is trans-1,2-bis(pyridin-4-yl)ethylene (C₁₂H₁₀N₂)]. The three hybrids consist of supramolecular networks built up by noncovalent interactions between {Fe[P₄Mo₆^VO₃₁]₂}^22- polyanions and protonated organic cations. This kind of hybrid polyoxometalate could be applied as heterogeneous molecular catalysts for the reduction of Cr^VI. It was found that the organic moiety plays a vital role in influencing the catalytic activity of the polyanions. Organic bpp-containing hybrids 1 and 2 are highly active in the catalytic reduction of heavy metal Cr^VI ions using HCOOH as reductant, while bpe-containing hybrid 3 is inactive to this reaction. This work is significant for the design of new catalysts, as well as the exploration of reaction mechanisms at a molecular level.

Polyoxometalate Cluster Sensitized with Copper-Viologen Framework for Efficient Degradation of Organic Dye in Ultraviolet, Visible, and Near-Infrared Light

An efficient photocatalyst based on the broadband solar response molecular system was designed and constructed for pollutant degradation in near-neutral conditions via utilizing guest polyoxometalate cluster sensitized with electron deficient host network. Photoelectrochemical analysis reveals electron-hole pairs are generated efficiently upon both visible and NIR light excitation. Its photocatalytic activity in the visible and NIR light regions is enhanced because of the contribution from the broad absorption of copper-viologen framework and the strong host-guest interactions. This stable heterogeneous catalyst is easily recollected and regenerated without the loss of activity for the next cycle.

An overview report on the application of heteropoly acids on supporting materials in the photocatalytic degradation of organic pollutants from aqueous solutions

Organic pollutants contaminate water resources and the environment when discharged into water streams. Also, the presence of these materials in incompletely treated or untreated wastewater leads to serious environmental hazards. The hydroxyl radicals and holes are regarded as the most oxidant species in the degradation of organic pollutants using the studied composites. The results of this review show that heteropoly acids on supporting materials could be considered as appropriate photocatalysts in the removal of organic pollutant from aqueous solutions.

Hydrothermal synthesis and crystal structure of a bisupporting Keggin-polyoxometalate hybrid compound decorated with a copper(II) complex unit

A bisupporting Keggin-type polyoxometalate compound, {[CuII(phen)2]2[(HBW12O40)]}[CuIICl2(phen)]2· 2H2O (phen=1,10-phenathroline) (1), has been synthesized through the hydrothermal method and characterized by IR spectroscopy, elemental analysis, UV/Vis/NIR spectroscopy, and powder and single crystal X-ray diffraction. The bisupporting Keggin-polyoxometalate consists of one Keggin-type [HBW12O40]4−core and two covalently linked copper(II) complex fragments [Cu(phen)2]2+. In the crystal structure π···π interactions, C–H···Cl, O–H···Cl, O–H···O and C–H···O hydrogen bonds lead to a three-dimensional supramolecular structure.

Construction of (3,6)-connected polyoxometalate-based metal–organic frameworks (POMOFs) from triangular carboxylate and dimerized Zn4-ε-Keggin

The methodology of extension of reduced transition metal-grafted ε-Keggin polyoxoanions with two types of terphenyl-based tricarboxylates was used to isolate two (3,6)-connected 3D POMOFs.

Lanthanide functionalized hybrid materials of polyoxometallate based metal–organic frameworks for multi-color luminescence

Lanthanide functionalized hybrids of polyoxometallate based MOF Ln³⁺⊂COK-15 are prepared and display multi-color light, together with a white luminescence (x = 0.3845, y = 0.303) by tuning an appropriate amount of Eu³⁺ and a suitable excitation wavelength.

The copper(i) metal azolate framework showing unusual coordination mode for the 1,2,4-triazole derivative and photocatalytic activity

A novel photocatalyst containing a tetranuclear Cu₄ cluster constructed by six 1,2,4-triazole units was reported where two of the six 1,2,4-triazole units show unusual bridging “crevice” coordination mode with their 1- and 2-positioned sp² N-atoms as symmetrically bridging centers.

An organic–inorganic hybrid photocatalyst based on sandwich-type tetra-Co-substituted phosphotungstates with high visible light photocatalytic activity

A novel hybrid photocatalyst constructed from tetra-Co^II-substituted sandwich-type phosphotungstates exhibits highly efficient visible light photocatalysis activity.

The first tritopic bridging ligand 1,3,5-tris(4-carboxyphenyl)-benzene (H3BTB) functionalized porous polyoxometalate-based metal–organic framework (POMOF): from design, synthesis to electrocatalytic properties

A POMOF with substantial catalytic activity towards bromate reduction was isolated through the extension of transition-metal-grafted ε-Keggin by a tripodal ligand H₃BTB.

Organic–inorganic hybrid assemblies based on Ti-substituted polyoxometalates for photocatalytic dye degradation

New organic–inorganic hybrid compounds based on Ti-substituted polyoxometalates exhibit high photocatalytic dye (MB) degradation activities.

Two hybrid materials assembled from transition metal mono-substituted Keggin polyoxoanions as photocatalysts under visible light

Two novel hybrid materials assembled from transition metal mono-substituted Keggin polyoxoanions with an antenna molecule were obtained and exhibit photocatalytic activity under visible light.