Two nickel-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24via WO4/Sb2O bridges and Ni-O-W linkages with efficient hydrogen evolution activity

Two Ni-added poly(polyoxometalate)s built of Keggin-type {Ni6PW9} and Anderson-type NiW6O24 units via WO4/Sb2O bridges and Ni-O-W linkages, Na4H8[Ni(enMe)2][(Sb2O)2(NiW6O24)-{Ni12O2(OH)4(enMe)4(H2O)3(WO4)2(B-α-PW9O34)2}2]·39H2O (1) and H9[Ni(en)2(H2O)][Ni0.5(en)2(H2O)][Ni-(enMe)2(H2O)][(Sb2O)2(NiW6O24){Ni12O2(OH)4(en)2(enMe)2(H2O)3(WO4)2}-{Ni12O2(OH)4(en)4(H2O)3(WO4)2}(B-α-PW9O34)4]·45H2O (2), have been hydrothermally synthesized and characterized, in which the {Ni12(WO4)2(PW9)2} subunit was obtained by the synergistic directing effect of 2 lacunary PW9O34 (PW9) fragments and further linked by a central Anderson-type (Sb2O)2(NiW6O24) bridge. Both compounds represent the first example of Ni-added polyoxometalates (POMs) simultaneously based on Keggin-type and Anderson-type POM components. Photocatalytic studies revealed that 2 can work as an efficient heterogeneous catalyst towards a light-driven H2 evolution reaction, achieving a hydrogen evolution rate of as high as 19 214 μmol g-1 h-1 (TON = 1500), which is superior to most of the reported POM-based heterogeneous catalysts.

{SeO2(OH)} Bridging Lanthanide-Containing Antimono-Seleno-Tungstates

A series of new trigonal pyramidal {SeO2(OH)} bridging lanthanide-containing antimono-seleno-tungstates [H2N(CH3)2]8Na8Cs4H9[Ln2SeW4O11(OH)(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33)]2·32H2O [Ln = Tb (1), Dy (2), Ho (3), Er (4)] have been prepared by the synthetic strategy of simultaneously using the antimonotungstate precursor and simple material in an acidic aqueous solution and structurally characterized by single-crystal X-ray diffraction, powder X-ray diffraction, IR spectrometry, and thermogravimetric analysis. Their molecular structures contain an unprecedented hexameric polyoxoanion [Ln2SeW4O11(OH)(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33)]229- constituted by two equivalent trimeric subunits Ln2W4O9(H2O)4(SbW9O33)(SeW9O33)(Se1/2Sb1/2W9O33) bridged via two μ2-{SeO2(OH)} linkers. Furthermore, the catalytic oxidation of various aromatic sulfides and sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES) by compound 3 as the heterogeneous catalyst has been investigated, exhibiting high conversion and selectivity as well as good stability and recyclability.

A wheel-shaped Zr-substituted phosphotungstate [{Zr(C2O4)2}3 (PO4)(P6W39O150)]39- with tunable proton conduction properties

A wheel-shaped Zr-substituted phosphotungstate, [N(CH3)4]2K16Na10.5H10.5[{Zr(C2O4)2}3(PO4)(P6W39O150)]·45H2O (1), was synthesised from a hexavacant Dawson-type precursor [H2P2W12O48]12-via a conventional solution method. Compound 1 features a wheel-shaped polyanion comprising an annular [P6W39O150]36- cluster supported by a turbine-shaped [{Zr(C2O4)2}3(PO4)]3- fragment, with three oxalate groups covalently anchored to W atoms. Compound 1 was systematically characterized by IR, UV, PXRD, TGA and 31P NMR spectra. The 31P NMR spectra over time were monitored to verify the stability of 1 in aqueous solution. This compound possesses remarkable proton conductive behavior with a high conductivity of 1.18 × 10-2 S cm-1 at 368 K.

A Zr-added Dawson-type poly(polyoxometalate)

A novel Zr-added trimer, [H₂N(CH₃)₂]₁₀H₁₄[(Zr₂P₂W₁₆O₆₁)₃]·7H₂O (1), has been made under hydrothermal conditions, and contains the highest number of Zr centers in known Dawson-type poly(POM)s. A remarkable feature of this study is the first discovery of a new type of divacant [α-5,10-P₂W₁₆O₆₀]^14- fragment, which assembles with Zr⁴⁺ ions to form a cyclic trimer. Furthermore, 1 as a heterogeneous catalyst exhibits high activity for the selective oxidative degradation of a sulfur mustard simulant CEES.

Recent Advances of Ti/Zr-Substituted Polyoxometalates: From Structural Diversity to Functional Applications

Polyoxometalates (POMs), a large family of anionic polynuclear metal-oxo clusters, have received considerable research attention due to their structural versatility and diverse physicochemical properties. Lacunary POMs are key building blocks for the syntheses of functional POMs due to their highly active multidentate O-donor sites. In this review, we have addressed the structural diversities of Ti/Zr-substituted POMs based on the polymerization number of POM building blocks and the number of Ti and Zr centers. The synthetic strategies and relevant catalytic applications of some representative Ti/Zr-substituted POMs have been discussed in detail. Finally, the outlook on the future development of this area is also prospected.

Hybrid Cu-Containing Compounds Based on Lacunary Strandberg Anions: Synthesis under Mild Conditions, Crystal Structure, and Magnetic Properties

A one-pot reaction of a copper source (metallic powder Cu⁰ or Cu²⁺ salts) and bpy (bpy = 2,2'-bipyridine) in the presence of (NH₄)₂HPO₄ and (NH₄)₆Mo₇O₂₄·4H₂O yields heterometallic hybrid compounds of the general type {[Cu(bpy)_n(H₂O)_m]_p[P₂Mo_xO_y]}. The structures exhibit a number of phosphomolybdate POMs including not only a common Strandberg anion [P₂Mo₅O₂₃]^6- but also its unprecedented bi- and trilacunary derivatives [P₂Mo₃O₁₈]^8- and [P₂Mo₂O₁₅]^8-. The structural determinants including the metal source (copper powder vs copper salts), counterion of the salts, and stoichiometry of the reagents were examined. An ex situ EPR study revealed the formation of different Cu^II complexes in the reaction mixture depending on the copper precursor. The obtained compounds have been found to possess selectivity toward the sorption of methylene blue in a mixture of organic dyes. DC magnetic measurements of 1-3 indicate rather strong antiferromagnetic metal-metal exchange interactions. Compound 1 exhibits field-induced slow magnetic relaxation in AC magnetic measurements, which is a rarely observed phenomenon among Cu(II) complexes.

Three ring-shaped Zr(iv)-substituted silicotungstates: syntheses, structures and their properties

Three Zr(iv)-substituted polyoxometalate nanoclusters, H₁₆(H₂dap)₄[{Zr₂(OH)₂(α-SiW₁₀O₃₈)}₂{Zr₂(OH)₂(β-SiW₁₀O₃₈)}₂]·8H₂O (1, dap = 1,3-diaminopropane), H₁₇Na₉[(Zr₂(OH)₂)₂(Zr₂BO(OH)₄)₂(β-SiW₁₀O₃₈)₄]·50H₂O (2) and H₂₀Na₈[(Zr₂BO(OH)₄)₂(Zr₂B₂O₂(OH)₅)₂(β-SiW₁₀O₃₈)₄]·40H₂O (3), were made by a hydrothermal reaction of trivacant [A-α-SiW₉O₃₄]^10-, Zr⁴⁺ ions, and H₃BO₃ under different alkaline conditions. Single-crystal X-ray structure analysis revealed that they are ring-shaped polyoxotungstate aggregates built by Zr₂(OH)₂ ({Zr₂}) clusters and two types of dilacunary α-/β-SiW₁₀O₃₈ ({α-/β-SiW₁₀}) fragments for 1, {Zr₂}, {β-SiW₁₀}, and Zr₂BO(OH)₄ ({Zr₂B}) clusters for 2, and {β-SiW₁₀}, {Zr₂B}, and Zr₂B₂O₂(OH)₅ ({Zr₂B₂}) clusters for 3, respectively, showing that the Zr-B-O clusters, {Zr₂B} and {Zr₂B₂}, have been introduced to the lacunary sites of polyoxometalates for the first time. The electrochemistry and electrocatalytic properties of 2 were studied, and it exhibited effective catalytic activities for the reduction of H₂O₂, NO₂^-, and BrO₃^-. Moreover, the catalysis of 2 for the oxidation reactions of various thioethers was investigated, and it was found that 2 possessed high conversion and remarkable selectivity.

Two unusual nanosized Nd3+-substituted selenotungstate aggregates simultaneously comprising lacunary Keggin and Dawson polyoxotungstate segments

Two unique nanosized Nd³⁺-substituted selenotungstates Na₉K₈{[W₃Nd₂(H₂O)₃(NO₃)O₆](B-α-SeW₉O₃₃)₂(α-Se₂W₁₄O₅₂)}·35H₂O (1) and [H₂N(CH₃)₂]₇H₉Na₄{[W₂Nd₂(H₂O)₈O₆(OH)₂(β-Se₂W₁₄O₅₂)][W₃Nd₂(H₂O)₆O₇(B-α-SeW₉O₃₃)₂]₂}·84H₂O (2) were prepared by reacting NaSeO₃, Na₂WO₄·2H₂O with Nd(NO₃)₃·6H₂O in aqueous solution by controlling different cations and pH values. 1 was synthesized at pH = 4.3 in the presence of KCl, whereas 2 was synthesized at pH = 3.0 in the presence of [H₂N(CH₃)₂]·Cl. The most striking structural feature of 1 and 2 is the coexistence of vacant Keggin and Dawson segments in the polyoxoanion, which is extremely rare in the field of polyoxometalate chemistry. The trimeric polyoxoanion of 1 can be perceived as a fusion of one α-type tetravacant Dawson [α-Se₂W₁₄O₅₂]^14- unit and two trivacant Keggin [B-α-SeW₉O₃₃]^8- segments sealing a trigonal bipyramid pentanuclear [W₃Nd₂(H₂O)₃(NO₃)O₆]¹¹⁺ cluster, while the pentameric polyoxoanion of 2 can be described as one β-type tetravacant Dawson [β-Se₂W₁₄O₅₂]^14- fragment and four trivacant Keggin [B-α-SeW₉O₃₃]^8- segments anchoring a saddle-shaped [W₈Nd₆(H₂O)₂₀O₂₀(OH)₂]²⁴⁺ cluster. In addition, the measurements of catalytic oxidation of aromatic thioethers show that 2 as a catalyst possesses extremely outstanding catalytic performance under mild reaction conditions.

Self-Assembly of Nanoscale Lanthanoid-Containing Selenotungstates: Synthesis, Structures, and Magnetic Studies

The reaction of mid-lanthanide (Ln) ions with the preformed {Se₆W₃₉} precursor under reasonably acidic aqueous conditions in the presence of organic amine cations results in an unprecedented nanoscale lanthanide-functionalized polyoxotungstate family, which are rare examples of mid-lanthanide-containing selenotungstates. (C₄H₁₀NO)₉Na₃[Dy₃Se_3.5W₃₀O_107.5(H₂O)₁₀]·22H₂O (1) and (NH₄)₃(C₂H₈N)Na₂[Dy₄Se₆W₃₈O₁₃₂(H₂O)₂₆(OH)₆]·18H₂O (2) reveal a trimeric Keggin assembly and a cyclic {Se₆W₃₈}-based chain, respectively, whereas (NH₄)₄Na₈[Gd₄Se₆W₄₈O₁₆₆(H₂O)₂₀(OH)₄]·21H₂O (3) and (NH₄)₉(C₂H₈N)₄Na₅[Ln₆Se₆W₅₈O₂₀₂(H₂O)₂₀(OH)₄]·58H₂O (4; Ln = Gd, Tb, or Dy) are a few examples of polyoxometalates consisting of both classical Keggin and Wells-Dawson building blocks, and (NH₄)₄(C₂H₈N)₅Na₁₃[Ln₄Se₈W₅₆O₁₉₆(H₂O)_x(OH)₁₀]·40H₂O (5; Ln = Gd, Tb, or Dy; x = 12 for Gd and Tb and 10 for Dy) features the largest "pure" Wells-Dawson selenotungstate {Se₈W₅₆} bearing a length of 3.73 nm. A library of Se-templated species involving the first reported Keggin {α-SeW₈} and Wells-Dawson {α-Se₂W₁₆} building blocks as well as some decisive assembly factors during the synthesis is responsible for these architectures. All of the compounds were structurally characterized in the solid and solution by single-crystal X-ray diffraction, IR, thermogravimetric-differential thermal analysis, and electrospray ionization mass spectrometry. Magnetic properties indicate that 1 and 4-Dy show probable single-molecule-magnet behavior with obvious frequency dependence, whereas 3 and 4-Gd present the antiferromagnetic interactions between the Gd^III centers.

Syntheses, Structures, and Electrochemical Properties of Three New Acetate-Functionalized Zirconium-Substituted Germanotungstates: From Dimer to Tetramer

Under hydrothermal conditions, three new acetate-functionalized zirconium-substituted polyoxometalates, H₄Na₂[Na₆(H₂O)₂₂][Zr₄(μ₃-O)₂(OH)₂(OAc)₂(α-GeW₁₀O₃₇)₂]·32H₂O (1), H₈K₃Na₅[Zr₆(μ₃-O)₃(OH)₃(OAc)(H₂O)(β-GeW₁₀O₃₇)₃]·20H₂O (2), H₆K₄Na₁₂[{Zr₅(μ₃-OH)₄(OH)₂}@{Zr₂(OAc)₂(α-GeW₁₀O₃₈)₂}₂]·22H₂O (3), were synthesized and characterized. In 1, the sandwiched dimer [Zr₄(μ₃-O)₂(OH)₂(OAc)₂(α-GeW₁₀O₃₇)₂]^12- was linked to a hexameric [Na₆(H₂O)₂₂]⁶⁺ cluster to form a 1D chain. In 2, the trimer was constructed from three [β₂-GeW₁₀O₃₇]^10- units and a new [Zr₆O₃(OH)₃(OAc)(H₂O)]¹⁴⁺ cluster. In 3, the tetramer was built by two novel sandwich-type dimers [Zr₂(OAc)₂(α₂-GeW₁₀O₃₈)₂]^18- and one unique [Zr₅(μ₃-OH)₄(OH)₂]¹⁴⁺ core in an approximately orthogonal fashion, showing a staggered tetrahedral polyanion. Also, the electrochemistry and electrocatalytic properties of 3 were studied, exhibiting good catalytic activities toward the reduction of H₂O₂, BrO₃^-, and NO₂^-.

Syntheses, structures and properties of three organic–inorganic hybrid polyoxotungstates constructed from {Ni6PW9} building blocks: from isolated clusters to 2-D layers

Three organic–inorganic hybrid POMs were prepared and characterized, exhibiting 0-D to 2-D assemblies made by {Ni₆PW₉} SBUs and organic ligands.

An unprecedented Zr-containing polyoxometalate tetramer with mixed trilacunary/dilacunary Keggin-type polyoxotungstate units

A novel zirconium(IV)-substituted tetramer polyoxotungstate, H₆K₄Na₁₆[Zr₄(β-GeW₁₀O₃₈)₂(A-α-PW₉O₃₄)₂]·37H₂O, was synthesized hydrothermally and characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, energy-dispersive X-ray spectroscopy and single-crystal X-ray diffraction. The compound crystallizes in the monoclinic P2/n space group. The most remarkable feature is that the centrosymmetric Zr-based polyoxotungstate tetramer consists of dilacunary Keggin-type germanotungstate and trilacunary Keggin-type phosphotungstate units that are linked by Zr^IV ions.

A new tetra-Zr(iv)-substituted polyoxotungstate aggregate

A new tetra-Zr(iv)-substituted tungstophosphate [H₂N(CH₃)₂]₆Na₆H₈{Zr₂[SbP₂W₄(OH)₂O₂₁][α₂-PW₁₀O₃₈]}₂·50H₂O has been made and structurally characterized. Its electrochemical and electrocatalytic properties have also been investigated.