Lanthanide-Connecting and Lone-Electron-Pair Active Trigonal-Pyramidal-AsO3 Inducing Nanosized Poly(polyoxotungstate) Aggregates and Their Anticancer Activities

Recent advances in lanthanide-based POMs for photoluminescent applications

Since the first formation of the famous "Peacock-Weakley" anions [Ln(W5O18)2]8/9-, a steady stream of breakthroughs have been made in the chemistry of multitalented lanthanide (Ln)-based polyoxometalates (POMs) for their potentially desirable properties. In particular, LnIII ions are generally recognised as the "vitamins of the modern industry" owing to their ability to cover a wide emission range, endowing Ln-based POMs with great potential for versatile and diverse luminescence-related applications. In this frontier, we discuss the synthesis strategies and intramolecular energy transfer in Ln-based POM derivatives. Then, the progressive improvements achieved with Ln-based POMs in photoluminescence applications are highlighted, focusing mainly on luminescent and fluorescent probes. Finally, the challenges for Ln-based POM materials for photoluminescence applications are discussed.

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.

Three Lanthanide-Functionalized Antimonotungstate Clusters with a {Sb4O4Ln3(H2O)8} Core: Syntheses, Structures, and Properties

Three lanthanide (Ln)-functionalized antimonotungstate (AT) clusters with a {Sb₄O₄Ln₃(H₂O)₈} core [H₂N(CH₃)₂]₁₄Na₈H₁₆[Sb₄O₄Ln₃(H₂O)₈W₂O₄(H₂O)₂(B-α-SbW₉O₃₃)₄]₂·87H₂O [Ln = Dy³⁺ (1), Ho³⁺ (2), Y³⁺ (3)] were synthesized in an acidic aqueous solution. Their molecular structural unit comprises two {Sb₄O₄Ln₃(H₂O)₈}-core-incorporated tetrameric [Sb₄O₄Ln₃(H₂O)₈W₂O₄(H₂O)₂ (B-α-SbW₉O₃₃)₄]^19- polyanionic units, each of which is assembled from an unprecedented [Sb₄O₄Ln₃(H₂O)₈W₂O₄(H₂O)₂]¹⁷⁺ heteroatom cluster surrounded by four trivacant [B-α-SbW₉O₃₃]^9- subunits. What is noteworthy is that a tetrahedral {Sb₄O₄} cluster is located at the center of the polyanionic unit, as far as we know, which is very infrequent in multi-Ln-functionalized polyoxometalate chemistry. Solid-state luminescent properties and energy migration of AT ligands to Dy³⁺ and Ho³⁺ cations in 1 and 2 have been intensively probed at ambient temperature. By varying the exciting wavelength from 250 to 450 nm, the emitting color could vary from blue to yellow for 1 and blue to green-yellow for 2, separately. In addition, high catalytic activities and good reusability of 2 as a heterogeneous catalyst for oxygenation reaction of sulfides have been systematically performed.

{Ti6}/{Ti10} Wheel Cluster Substituted Silicotungstate Aggregates

Two novel Ti-oxo wheel cluster substituted silicotungstates (STs) [H₂N(CH₃)₂]₉H₉[Ti₆O₆(SiW₁₀O₃₇)₃]·11H₂O (1) and [H₂N(CH₃)₂]₁₆H₁₀[Ti₁₀O₁₁(SiW₁₀O₃₇)₂(SiW₉O₃₅)₂]·14H₂O (2) have been made by hydrothermal reactions. The polyoxoanion of 1 is a ring-shaped trimer where a Ti₆O₆ ({Ti₆}) wheel cluster is encapsulated by three divacant [SiW₁₀O₃₇]^10- (SiW₁₀O₃₇) fragments. However, 2 is built by two divacant SiW₁₀O₃₇ units and two rare trivacant [SiW₉O₃₅]^12- (SiW₉O₃₅) fragments and further installs an unprecedented Ti₁₀O₁₁ ({Ti₁₀}) double-wheel cluster. To the best of our knowledge, 2 is rare in POM chemistry. Studies on the catalytic oxidation properties reveal that 1 exhibits high catalytic activity toward the oxidation of various sulfides using H₂O₂ as an oxidant. Furthermore, 1 can be facilely recycled and reused for at least five cycles without obvious loss of catalytic activity.

Multicomponent Self-Assembly of a Giant Heterometallic Polyoxotungstate Supercluster with Antitumor Activity

The hierarchical aggregation of molecular nanostructures from multiple components is a grand synthetic challenge, which requires highly selective linkage control. We demonstrate how two orthogonal linkage groups, that is, organotin and lanthanide cations, can be used to drive the aggregation of a giant molecular metal oxide superstructure. The title compound {[(Sn(CH3 )2 )2 O]4 {[CeW5 O18 ] [TeW4 O16 ][CeSn(CH3 )2 ]4 [TeW8 O31 ]4 }2 }46- (1 a) features dimensions of ca. 2.2×2.3×3.4 nm3 and a molecular weight of ca. 25 kDa. Structural analysis shows the hierarchical aggregation from several independent subunits. Initial biomedical tests show that 1 features an inhibitory effect on the proliferation of HeLa cells based on an apoptosis pathway. In vivo experiments in mice reveal the antiproliferative activity of 1 and open new paths for further development of this new compound class.

Assembly of Lanthanide-Containing Tungstotellurates(VI): Syntheses, Structures, and Catalytic Properties

Lanthanide (Ln)-containing polyoxometalates (POMs) have attracted particular attention owing to their structural diversity and potential applications in luminescence, magnetism, and catalysis. Herein three types of Ln-containing tungstotellurates(VI) (Ln = Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, and Lu³⁺), dimeric (DMAH)_n[H_22−n{Ln(H₂O)₃[TeW₁₇O₆₁]}₂]^·mH₂O (abbreviated as {Ln₂Te₂W₃₄}; DMAH⁺ = dimethylammonium), mono-substituted (DMAH)₇Na₂{H₂Ln(H₂O)₄[TeW₁₇O₆₁]}^·mH₂O (abbreviated as {LnTeW₁₇}), and three-dimensional (3D) inorganic frameworks (DMAH)_n{H_3−nLn(H₂O)₄[TeW₆O₂₄]}^·mH₂O (abbreviated as {LnTeW₆}), have been synthesized by using simple metal salts and characterized by single-crystal X-ray diffraction and other routine techniques. Interestingly, the assembly of these POMs is pH dependent. Using the same starting materials, {Ln₂Te₂W₃₄} were obtained at pH 1.7, where two Dawson-like monovacant [TeW₁₇O₆₁]¹⁴⁻ are linked by two Ln³⁺ ions; mono-substituted Dawson-like {LnTeW₁₇} were isolated at pH 1.9, and 3D inorganic framework {LnTeW₆} based on Anderson-type [TeW₆O₂₄]⁶⁻ were formed at pH 2.3. It was also found that the assembly of Ln-containing POMs depends on the type of Ln³⁺ ions. The three types of POMs can be prepared by using Ln³⁺ ions with a relatively smaller ionic radius, such as Tb³⁺-Lu³⁺, while the use of Ln³⁺ ions (La³⁺-Eu³⁺) results in the formation of precipitation or {TeW₁₈O₆₂} clusters. Furthermore, three {LnTeW₆} (Ln = Tb³⁺, Er³⁺, Lu³⁺) were used as Lewis acid catalysts for the cyanosilylation of benzaldehydes, and their catalytic activity decreases with the decrease of Ln³⁺ ionic radius, giving the order: {TbTeW₆} > {ErTeW₆} > {LuTeW₆}. Notably, {TbTeW₆} is stable to leaching and can be reused for five cycles without a significant loss of its activity.

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.

An unprecedented polyhydroxycarboxylic acid ligand bridged multi-EuIII incorporated tellurotungstate and its luminescence properties

The first polyhydroxycarboxylic acid ligand bridged multi-EuIII-incorporated tellurotungstate K14H10[Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]·60H2O (H6glu = d-gluconic acid) (1) was synthesized via an organic ligand-driven self-assembly strategy. The polyhydroxycarboxylic acid ligand bridged tetrameric polyoxoanion [Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]24- in 1 can be viewed as an aggregation of four trivacant Keggin [B-α-TeW9O33]8- fragments and an innovative heterometallic [Eu4(H2O)4W6(H2glu)4O12]8+ cluster, in which four high-coordinate polyhydroxy flexible H2glu4- ligands chelate W and Eu centers through carboxyl and hydroxyl groups, giving rise to a heterometallic cluster. The hexagonal packing of the tetrameric polyoxoanions in 1 along the c axis provides excellent porous channels, which greatly increases the specific surface area of the whole framework and may be of benefit for fluorescence sensing in aqueous solution. 1 can function as a "turn-off" luminescence sensor to detect Cu2+ ions in aqueous solution. The limit of detection (LOD) of the 1-sensor is 8.82 × 10-6 mM, which is the lowest among the reported polyoxometalate-based fluorescence sensors. As for the Cu2+-quenching system, it can function as an "off-on" sensor to detect cysteine in an aqueous system, affording a LOD of 1.75 × 10-4 mM. This work opens up an avenue to broaden the applications of polyoxometalate-based materials in the optical intelligence detection field.

First series of mixed (PIII, SeIV)-heteroatomoriented rare-earth-embedded polyoxotungstates containing distinct building blocks

A series of unprecedented mixed heteroatoms-oriented rare-earth-embedded heteropolyoxotungstates 1–8 were prepared and the 1@CMWCNT-GCE electrochemical sensing performances toward DA and UA were studied.

The Intrinsic Enzyme Activities of the Classic Polyoxometalates

The mimicking enzyme activities of eighteen classic POMs with different structures, Keggin (H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₄GeW₁₂O₄₀, K₄GeW₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiMo₁₂O₄₀ and Eu₃PMo₁₂O₄₀), Wells-Dawson (H₆P₂Mo₁₈O₆₂, α-(NH₄)₆P₂W₁₈O₆₂ and α-K₆P₂W₁₈O₆₂·14H₂O), lacunary-Keggin (Na₈H[α-PW₉O₃₄], Na₁₀[α-SiW₉O₃₄], Na₁₀[α-GeW₉O₃₄] and K₈[γ-SiW₁₀O₃₆]), the transition-metal substituted-type (α-1,2,3-K₆H[SiW₉V₃O₃₄] and H₅PMo₁₀V₂O₄₀), sandwich-type (K₁₀P₂W₁₈Fe₄(H₂O)₂O₆₈) and an isopolyoxotungstate (Na₁₀H₂W₁₂O₄₂) were screened and compared. The mechanisms and reaction conditions of POMs with mimicking enzyme-like activities were also analyzed. The results shown that the structures, the hybrid atoms, the coordination atoms, the substituted metal atoms, pH and substrate are the effect factors for the enzyme mimic activities of POM. Among the eighteen POMs, H₃PW₁₂O₄₀, H₄SiW₁₂O₄₀, H₄GeW₁₂O₄₀, α-(NH₄)₆P₂W₁₈O₆₂, α-K₆P₂W₁₈O₆₂·14H₂O, Na₈H[α-PW₉O₃₄], Na₁₀[α-SiW₉O₃₄], Na₁₀[α-GeW₉O₃₄], K₈[γ-SiW₁₀O₃₆], K₁₀P₂W₁₈Fe₄(H₂O)₂O₆₈ and Na₁₀H₂W₁₂O₄₂ had the peroxidase activities. Eu₃PMo₁₂O₄₀, H₃PMo₁₂O₄₀, H₄SiMo₁₂O₄₀, α-1,2,3-K₆H [SiW₉V₃O₃₄], H₆P₂Mo₁₈O₆₂ and H₅PMo₁₀V₂O₄₀ showed the oxidase-like activities. K₄GeW₁₂O₄₀ did not show the peroxidase and oxidase activities. The Na₈H[α-PW₉O₃₄], Na₁₀[α-SiW₉O₃₄] and Na₁₀[α-GeW₉O₃₄] showed intrinsic enzyme activities at alkaline conditions, which were different from other type of POMs. The sandwich-type K₁₀P₂W₁₈Fe₄(H₂O)₂O₆₈ displayed the strongest peroxidase activity, which is similar to natural horseradish peroxidase.

Recent advances in isopolyoxotungstates and their derivatives

During the past decade, isopolyoxotungstates (iso-POTs) and their derivatives have been greatly developed due to their unique structures and potential applications in luminescence, magnetism, catalysis etc. This brief review is principally focused on the main research progress on iso-POTs, iso-POT-based transition-metal derivatives, iso-POT-based rare-earth derivatives, iso-POT-based organometallic derivatives and iso-POT-based heterometallic derivatives, and gives a summary of some representative examples of their syntheses, structures and related properties. In addition, an outlook on the future of this area is presented in the final section. We believe that this systematic commentary on iso-POTs and their derivatives will not only disclose a rich set of iso-POT structures, but also reveal a more promising direction for the further functionalization of iso-POTs.

First Dimethyltin-Functionalized Rare-Earth Incorporated Tellurotungstates Consisting of {B-α-TeW7O28} and {W5O18} Mixed Building Units

The facile one-step assembly reaction of Na₂WO₄·2H₂O, Sn(CH₃)₂Cl₂, RE(NO₃)₃·6H₂O and K₂TeO₃ in the presence of dimethylamine hydrochloride as an organic solubilizing agent in acidic aqueous solution resulted in a family of dimethyltin-functionalized rare-earth (RE) incorporated tellurotungstates consisting of {B-α-TeW₇O₂₈} and {W₅O₁₈} mixed building units [H₂N(CH₃)₂]₈Na₄H₂[RE₂(OH)(B-α-TeW₇O₂₈)Sn₂(CH₃)₄(W₅O₁₈)]₂·18H₂O [RE = Er^III (1), Yb^III (2), Ho^III (3), Y^III (4)]. The most striking structural characteristic of 1-4 is that they all contain a novel tetrameric S-shaped [RE₂(OH)(B-α-TeW₇O₂₈)Sn₂(CH₃)₄(W₅O₁₈)]₂^14- moiety simultaneously including two pentavacant Keggin [B-α-TeW₇O₂₈]^12- and two monovacant Lindqvist [W₅O₁₈]^6- fragments connected by RE and dimethyltin linkers. To the best of our knowledge, such dimethyltin-functionalized RE-containing tellurotungstates have not been reported before. The visible or NIR solid-state emission spectra of 1 and 3 display the characteristic emission bands arising from Er^III and Ho^III centers. Moreover, various 1-Er/Yb co-doped samples were prepared by controlling different mass ratio of Er(NO₃)₃·6H₂O/Yb(NO₃)·6H₂O in the range of 0.96:0.04-0.02:0.98. In the visible region, the emission intensity of the 1-Er_0.40/Yb_0.60 co-doped sample reaches the maximum at the mass ratio of Er(NO₃)₃·6H₂O/Yb(NO₃)·6H₂O being 0.40:0.60, and this observation is mainly derived from the fact that the Yb³⁺ ions can sensitize the Er³⁺ ions to enhance the emission intensity in the visible region. However, no such phenomenon for the 1-Er/Yb co-doped samples is seen in the NIR region. Besides, the upconversion spectra of the 1-Er/Yb co-doped samples were first observed. In addition, the thermal stabilities of 1-4 were also investigated on the crystalline samples and the thermal decomposition process of 1 has been deeply studied.

Aggregation of Giant Cerium-Bismuth Tungstate Clusters into a 3D Porous Framework with High Proton Conductivity

The exploration of high nuclearity molecular metal oxide clusters and their reactivity is a challenge for chemistry and materials science. Herein, we report an unprecedented giant molecular cerium-bismuth tungstate superstructure formed by self-assembly from simple metal oxide precursors in aqueous solution. The compound, {[W₁₄ Ce^IV₆ O₆₁ ]([W₃ Bi₆ Ce^III₃ (H₂ O)₃ O₁₄ ][B-α-BiW₉ O₃₃ ]₃ )₂ }^34- was identified by single-crystal X-ray diffraction and features 104 metal centers, a relative molar mass of ca. 24 000 and is ca. 3.0×2.0×1.7 nm³ in size. The cluster anion is assembled around a central {Ce₆ } octahedron which is stabilized by several molecular metal oxide shells. Six trilacunary Keggin anions ([B-α-BiW₉ O₃₃ ]^9- ) cap the superstructure and limit its growth. In the crystal lattice, water-filled channels with diameters of ca. 0.5 nm are observed, and electrochemical impedance spectroscopy shows pronounced proton conductivity even at low temperature.

Syntheses, structures and fluorescence properties of three rare-earth containing docosatungstates

Three rare-earth containing docosatungstates Na₃H₂[RE(H₂O)₄][RE(H₂O)₅]₂[W₂₂O₇₄H₂]·36H₂O [RE=Dy^III (1), Ho^III (2), Y^III (3)] have been synthesized by reaction of Na₂WO₄·2H₂O, dimethylamine hydrochloride (DMAHC) and RE(NO₃)₃·6H₂O in the aqueous solution and characterized by elemental analyses, IR spectra, thermogravimetric (TG) analysis, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. 1-3 are isomorphous and each molecular unit consists of a S-shaped docosatungstate [W₂₂O₇₄H₂]^14- polyoxoanion with two supporting [RE(H₂O)₅]³⁺ cations and one disordered [RE(H₂O)₄]³⁺ cation. The [W₂₂O₇₄H₂]^14- polyoxoanion can be viewed as combination of two hendecatungstate [W₁₁O₃₈H]^9- subunits in the staggered fashion by sharing two μ₂-O atoms. The TG curves of 1-3 reveal the one-step weight loss between 25°C to 700°C. Moreover, both 1 and 2 demonstrate the characteristic luminescence emission behaviors of the corresponding RE³⁺ ions and their lifetime decay curves can be well fitted to the double exponential function. In addition, the CIE chromaticity coordinates of 1 and 2 have been obtained based on their corresponding emission spectra, and their dominant wavelengths and color purities have been also calculated.