Stereoisomerism in polyoxometalates: structural and spectroscopic studies of bis(malate)-functionalized cluster systems

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.

Roles of Organic Fragments in Redirecting Crystal/Molecular Structures of Inorganic-Organic Hybrids Based on Lacunary Keggin-Type Polyoxometalates

Lacunary polyoxometalates (LPOMs) are key precursors for the synthesis of functional POMs. To date, reviews dedicated to behavioral studies of LPOMs often comprise the role of metal ions, including transition metal (TM) and rare earth (RE) ions, in extending and stability of high-nuclearity clusters. In contrast, the role of organic ligands in the structures and properties of lacunary-based hybrids has remained less explored. In this review, we focus on the role of organic fragments in the self-assembling process of POM-based architectures and discuss relationships between the nature and structure of organic ligand and properties such as the topology of hybrid inorganic–organic material in RE and TM-RE heterometallic derivatives of lacunary Keggin-type POMs. The effects of organic fragment in mixed ligand hybrids are also briefly reviewed.

Electrophilicity in heterogeneous catalysis: role of surface and sub-surface modification

Surface and sub-surface modification can play a significant role in improving the catalytic activity in designed systems.

Three Zr(IV)-Substituted Polyoxotungstate Aggregates: Structural Transformation from Tungstoantimonate to Tungstophosphate Induced by pH

Three novel Zr-substituted polyoxotungstate aggregates [H₂N(CH₃)₂]₇NaH₂[Zr₂Sb₂O₃(A-α-PW₉O₃₄)₂]·16H₂O (1), [H₂N(CH₃)₂]₆H₁₂[ZrSb₄(OH)O₂(A-α-PW₈O₃₂)(A-α-PW₉O₃₄)]₂·33H₂O (2), and [H₂N(CH₃)₂]₄Na_11.5H_4.5[Zr₄W₈Sb₄P₅O₄₉(OH)₅(B-α-SbW₉O₃₃)₂]·53H₂O (3) have been made in hydrothermal reactions of the [B-α-SbW₉O₃₃]^9- precursor with Zr⁴⁺ cations and PO₄^3- anions in the presence of dimethylamine hydrochloride and sodium acetate buffer (pH = 4.8) and structurally characterized. Different pH values induce structural transformation from tungstoantimonate (TA) to tungstophosphate (TP). 1 is a di-Zr-substituted sandwich-type TP, the tetranuclear heterometallic [Zr₂Sb₂O₃]⁸⁺ entity sandwiched by two [A-α-PW₉O₃₄]^9- moieties. 2 is a double sandwich-type structure, which can be perceived as two equivalent sandwiched [Sb₃(PW₈O₃₂)(PW₉O₃₄)]^11- further sandwiching one [Sb₂Zr₂(OH)₂O₄]⁴⁺ core to form a novel large-size sandwich-type architecture. Different from 1 and 2, 3 is a tetra-Zr-substituted sandwiched configuration, in which two [B-α-SbW₉O₃₃]^9- fragments sandwich a unique 21-core Sb-P-W-Zr oxo cluster ({Zr₄W₈Sb₄P₅}). Furthermore, the catalytic oxidation of aromatic thioethers by 3 as the heterogeneous catalyst has been investigated, showing high conversion and remarkable selectivity as well as excellent recyclability.

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^-.

Zr4-Substituted polyoxometalate dimers decorated by d-tartaric acid/glycolic acid: syntheses, structures and optical/electrochemical properties

Two Zr₄-sandwiched Keggin polyoxometalates functionalized by chiral d-tartaric acid and glycolic acid were hydrothermally synthesized and structurally characterized. Their optical and electrochemical properties have been investigated in detail.

A pair of new chiral polyoxovanadates with decent NLO properties

Through utilizing a two-step method to successfully prepare a pair of enantiomers trataric-polyoxovanadate [(l/d-C₄O₆H₂)₂V₄O₈]·2C₆N₂H₁₈ (1-L or 1-D), these compounds show decent third-order NLO property and electrochemical behavior.

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.

Discovery and isolation of the trans-isomers of two 1 : 2-type lanthanide-containing monolacunary Dawson-type tungstophosphates: [LnIII(α2-P2W17O61)2]17− (Ln = La, Ce)

Two novel trans-isomers of 1 : 2-type lanthanide-containing monolacunary Dawson-type tungstophosphates [Ln(α₂-P₂W₁₇O₆₁)₂]¹⁷⁻ (Ln = La^III (1), Ce^III (2)) were successfully isolated and characterized.

Coordination-Driven Self-Assembly of a 2D Graphite-Like Framework Constructed from High-Nuclear Ce10 Cluster Encapsulated Polyoxotungstates

It is challenging to explore and prepare high-nuclear lanthanide (Ln) cluster-encapsulated polyoxometalates (POMs). Herein, we fabricate an unprecedented Ce10-cluster-embedded polyoxotungstate (POT) (TMA)14H2[Ce(III)(H2O)6]{[Ce(IV)7Ce(III)3O6(OH)6(CO3)(H2O)11][(P2W16O59)]3}·41H2O (1) (TMA = tetramethyleneamine) by coordination-driven self-assembly strategy, which contains the largest Ce cluster [Ce(IV)7Ce(III)3O6(OH)6(CO3)(H2O)11] (Ce10) in all the Ln-containing POM chemistry to date. Self-assembly of the in situ dilacunary [P2W16O59](12-) fragments and mixed Ce(3+) and Ce(4+) ions by means of coordination-driven force results in a novel 2D graphite-like framework constructed from mixed-valent cerium(III/IV) cluster {Ce10} encapsulated poly(POT) units and Ce(3+) ions. The most remarkable feature is that the skeleton of the centrosymmetric Ce10-cluster-embedded POT trimer contains three dilacunary [P2W16O59](12-) fragments trapping a novel {Ce10} cluster via 18 terminal-oxo and three μ4-oxo atoms.

Synthesis and structural characterization of BINOL-modified chiral polyoxometalates

Chiral ligand-modified polyoxometalates (POMs) R-I and S-I were successfully synthesized by the introduction of BINOL into the dititanium-substituted POM.

Temperature-induced racemic compounds and chiral conglomerates based on polyoxometalates and lanthanides: syntheses, structures and catalytic properties

Four new species, originated from [Co₂Mo₁₀H₄O₃₈]⁶⁻ and lanthanides by adjusting the reaction temperature, are reported, which act as Lewis acid–base catalysts toward the cyanosilylation reaction.

Synthesis and characterization of robust three-dimensional chiral metal sulfates

Chiral three-dimensional Mg(ii) and Mn(ii) sulfates have been synthesized, well characterized and studied from first-principles calculations. High temperature X-ray diffraction, thermogravimetric analysis and DFT calculations reveal that the structures of both the compounds remain intact even after the thermal decomposition of the ammonium ion.

Polyoxometalate water oxidation catalysts and the production of green fuel

In the last five years and currently, research on solar fuels has been intense and no sub-area in this field has been more active than the development of water oxidation catalysts (WOCs). In this timeframe, a new class of molecular water oxidation catalysts based on polyoxometalates have been reported that combine the advantages of homogeneous and heterogeneous catalysts. This review addresses central issues in green energy generation, the challenges in water oxidation catalyst development, and the possible uses of polyoxometalates in green energy science.

A new organic-inorganic hybrid layered molybdenum(V) cobalt phosphate constructed from [H24(Mo16O32)Co16(PO4)24(OH)4(C5H4N)2(H2O)6](4-) wheels and 4,4'-bipyridine linkers

A new layered molybdenum cobalt phosphate, Na(2)[Co(H(2)O)(6)][(Mo(16)O(32))Co(16)(PO(4))(4) (HPO(4))(16)(H(2)PO(4))(4)(OH)(4)(C(10)H(8)N(2))(4)(C(5)H(4)N)(2)(H(2)O)(6)]·4H(2)O (1), has been hydrothermally synthesized and structurally characterized. 1 crystallizes in the monoclinic space group P2(1)/n with a = 15.6825(18) Å, b = 39.503(4) Å, c = 17.2763(17) Å, β = 93.791(2)°, V = 10679.4(18) Å(3), and Z = 2. A polyoxoanion of 1 exhibits an unusual organic-inorganic hybrid wheel-type cluster, in which two pyridine ligands link to the surface Co(II) atoms of a [H(24)(Mo(16)O(32))Co(16)(PO(4))(24)(OH)(4)(H(2)O)(6)] (namely, {Mo(16)Co(16)P(24)}) wheel via the Co-N bonds. Furthermore, each {Mo(16)Co(16)P(24)} wheel is connected to four adjacent wheels by four pairs of 4,4'-bipyridine linkers, forming a 2D layered network. The susceptibility measurement shows the existence of dominant antiferromagnetic interactions in 1.