Gallium(III)-Containing, Sandwich-Type Heteropolytungstates: Synthesis, Solution Characterization, and Hydrolytic Studies toward Phosphoester and Phosphoanhydride Bond Cleavage

An Innovative SbIII-WVI-Cotemplated Antimonotungstate with Potential in Sensing Paroxetine Electrochemically

Advances in polyoxometalate (POM) self-assembly chemistry are always accompanied by new developments in molecular blocks. The exploration and discovery of uncommon building blocks offer great possibilities for generating unprecedented POM clusters. An intriguing SbIII-WVI-cotemplated antimonotungstate [H2N(CH3)2]11Na[SbW9O33]Er2(H2O)2Sb2[SbWVIW15O57]·22H2O (1) was synthesized, which comprises a classical trivacant Keggin [SbW9O33]9- ({SbW9}) fragment and an unclassical lacunary Dawson-like [SbWVIW15O57]15- ({SbWVIW15}) subunit. Notably, the Dawson-like {SbWVIW15} subunit is the first example of a [SbO3]3- and [WVIO6]6- mixed-heteroatom-directing POM segment. Hexacoordinated [WVIO6]6- can not only serve as the heteroatom function but its additional oxygen sites can also link to lanthanide, main-group metal, and transition-metal centers to form the innovative structure. {SbWVIW15} and {SbW9} subunits are joined by the heterometallic [Er2(H2O)2Sb2O17]22- cluster to give rise to an asymmetric sandwich-type architecture. To further realize its potential application in electrochemical sensing, a conductive 1@rGO composite was obtained by the electrochemical deposition of 1 with graphene oxide (GO). Using a 1@rGO-modified glassy carbon electrode as the working electrode, an electrochemical biosensor for detecting the antidepressant drug paroxetine (PRX) was successfully constructed. This work can provide a viable strategy for synthesizing mixed-heteroatom-directing POMs and demonstrates the application of POM-based materials for the electrochemical detection of drug molecules.

Reactivity of metal-oxo clusters towards biomolecules: from discrete polyoxometalates to metal-organic frameworks

Metal-oxo clusters hold great potential in several fields such as catalysis, materials science, energy storage, medicine, and biotechnology. These nanoclusters of transition metals with oxygen-based ligands have also shown promising reactivity towards several classes of biomolecules, including proteins, nucleic acids, nucleotides, sugars, and lipids. This reactivity can be leveraged to address some of the most pressing challenges we face today, from fighting various diseases, such as cancer and viral infections, to the development of sustainable and environmentally friendly energy sources. For instance, metal-oxo clusters and related materials have been shown to be effective catalysts for biomass conversion into renewable fuels and platform chemicals. Furthermore, their reactivity towards biomolecules has also attracted interest in the development of inorganic drugs and bioanalytical tools. Additionally, the structural versatility of metal-oxo clusters allows for the efficiency and selectivity of the biomolecular reactions they promote to be readily tuned, thereby providing a pathway towards reaction optimization. The properties of the catalyst can also be improved through incorporation into solid supports or by linking metal-oxo clusters together to form Metal-Organic Frameworks (MOFs), which have been demonstrated to be powerful heterogeneous catalysts. Therefore, this review aims to provide a comprehensive and critical analysis of the state of the art on biomolecular transformations promoted by metal-oxo clusters and their applications, with a particular focus on structure-activity relationships.

Synthesis, Characterization, and Antibacterial Activity of Ni-Substituted Krebs-type Sandwich-Tungstobismuthates Functionalized with Amino Acids

Four new Ni-substituted Krebs-type sandwich-tungstobismuthates, K₄Ni₂[{Ni(β-ala)(H₂O)₂}₂{Ni(H₂O)}₂{Ni(H₂O)(η²-β-ala)}₂(B-β-BiW₉O₃₃)₂]·49H₂O {(β-ala)₄(Ni₃)₂(BiW₉)₂}, K_3.5Na_6.5[{Ni(η³-L-asp)}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·36H₂O·L-asp {(L-asp)₂(NiW)₂(BiW₉)₂}, K₄Na₆[{Ni(gly)(H₂O)₂}₂(WO₂)₂(B-β-BiW₉O₃₃)₂]·86H₂O {(gly)₂(NiW)₂(BiW₉)₂}, and K₂Na₈[{Ni(η²-serinol) (H₂O)}₂{Ni(H₂O)₂}₂(B-β-BiW₉O₃₃)₂]·42H₂O {(serinol)₂Ni₄(BiW₉)₂} have been synthesized by one-pot solution methods. All compounds have been characterized in the solid state by single-crystal X-ray diffraction (SXRD), powder X-ray diffraction (PXRD), elemental and thermogravimetric analyses, and infrared spectroscopy (IR), as well as by UV-vis spectroscopy in solution. The antibacterial activity of all compounds was studied against four bacterial strains by the determination of the minimum inhibitory concentration (MIC). The results showed that only {(β-ala)₄(Ni₃)₂(BiW₉)₂} demonstrates antibacterial activity (MIC is in the range from 8 to 256 μg/mL) compared to three other Ni-Krebs sandwiches.

Two Types of Subgroup-Valence Heteroatoms (PIII, TeIV) Synergistically Controlling Octa-CeIII-Encapsulated Heteropolyoxotungstate and Its Electrochemical Recognition Properties

Rapid development of the synthetic chemistry of polyoxometalates (POMs) has greatly driven the generation of structurally variable innovative POM-based materials. Herein, we synthesized a novel P^III and Te^IV synergistically controlling octa-Ce^III-encapsulated heteropolyoxotungstate [H₂N(CH₃)₂]₁₁K₂Na₆H₁₁[Ce₈(CH₃COO)₂(HP^IIIO₃)₂W₈O₂₀(H₂O)₁₂(B-β-TeW₈O₃₀)₂(B-α-TeW₈O₃₁)₄]·64H₂O (1). Its distinctive anion skeleton [Ce₈(CH₃COO)₂(HP^IIIO₃)₂W₈O₂₀(H₂O)₁₂(B-β-TeW₈O₃₀)₂(B-α-TeW₈O₃₁)₄]^30- is built by two tetra-vacancy [B-β-TeW₈O₃₀]^8- and four tetra-vacancy [B-α-TeW₈O₃₁]^10- moieties linked through an inorganic-organic hybrid [Ce₈(CH₃COO)₂(HP^IIIO₃)₂W₈O₂₀(H₂O)₁₂]²⁶⁺ {Ce₈P₂W₈} cluster core. Interestingly, {Ce₈P₂W₈} is assembled from four [W₂O₁₁]^10- groups and two [HP^IIIO₃]^2- anions and eight Ce³⁺ ions. Besides, 1 was further composited with carboxylated multiwalled carbon nanotube (CMCN), resulting in a bi-component 1/CMCN nanocomposite. An electrochemical recognition platform (named as 1/CMCN/GCE) was built by modifying 1/CMCN on a glassy carbon electrode (GCE) for electrochemical detection of dopamine (DPA) at physiological pH (pH = 7.0). The findings have shown that 1/CMCN/GCE exhibits a good detection limit of 4.95 nM for DPA. This work provides considerable inspiration to promote innovative and rational structure designs of POM-based materials and expand their applications to electrochemical and biological detection fields.

Trisubstituted 4f- and 4d tungstoantimonates as artificial phosphoesterases for nerve agent degradation

Three new trisubstituted 4f- and 4d tungstoantimonates (TA) K3Na21[(M(CH3COO))3(HPO3)(WO4)(SbW9O33)3]·nH2O {M3(HPO3)Sb3W28} (M = GdIII, YIII, YbIII, n = 35-36) were synthesized using a double-template synthetic approach. Following their characterization in the solid state employing single- and powder X-ray diffraction (XRD), IR-spectroscopy, and elemental - and thermogravimetric analyses (TGA), {M3(HPO3)Sb3W28} were subjected to a comprehensive set of solution characterization methods including UV/vis- and multinuclear 31P and 13C NMR spectroscopy. All representatives were shown to be highly active, recyclable, and stable Lewis-acid catalysts towards the nerve agent simulant O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) at neutral pH (in Tris-HCl [125 mM] at pD 7.0 25 °C). Control experiments showing catalytic activity of the unsubstituted trilacunary TA [SbW9O33]9- suggest the non-innocence of Tris in the DMNP hydrolysis for the first time.

Nuclease-like metalloscissors: Biomimetic candidates for cancer and bacterial and viral infections therapy

Despite the extensive and rapid discovery of modern drugs for treatment of cancer, microbial infections, and viral illnesses; these diseases are still among major global health concerns. To take inspiration from natural nucleases and also the therapeutic potential of metallopeptide antibiotics such as the bleomycin family, artificial metallonucleases with the ability of promoting DNA/RNA cleavage and eventually affecting cellular biological processes can be introduced as a new class of therapeutic candidates. Metal complexes can be considered as one of the main categories of artificial metalloscissors, which can prompt nucleic acid strand scission. Accordingly, biologists, inorganic chemists, and medicinal inorganic chemists worldwide have been designing, synthesizing and evaluating the biological properties of metal complexes as artificial metalloscissors. In this review, we try to highlight the recent studies conducted on the nuclease-like metalloscissors and their potential therapeutic applications. Under the light of the concurrent Covid-19 pandemic, the human need for new therapeutics was highlighted much more than ever before. The nuclease-like metalloscissors with the potential of RNA cleavage of invading viral pathogens hence deserve prime attention.

Phosphate-Templated Encapsulation of a {CoII 4 O4 } Cubane in Germanotungstates as Carbon-Free Homogeneous Water Oxidation Photocatalysts

The ever-growing interest in sustainable energy sources leads to a search for an efficient, stable, and inexpensive homogeneous water oxidation catalyst (WOC). Herein, the PO₄ ^3- templated synthesis of three abundant-metal-based germanotungstate (GT) clusters Na₁₅ [Ge₄ PCo₄ (H₂ O)₂ W₂₄ O₉₄ ] ⋅ 38H₂ O (Co₄ ), Na_2.5 K_17.5 [Ge₃ PCo₉ (OH)₅ (H₂ O)₄ W₃₀ O₁₁₅ ] ⋅ 45H₂ O (Co₉ ), Na₆ K₁₆ [Ge₄ P₄ Co₂₀ (OH)₁₄ (H₂ O)₁₈ W₃₆ O₁₅₀ ] ⋅ 61H₂ O (Co₂₀ ) with non-, quasi-, or full cubane motifs structurally strongly reminiscent of the naturally occurring {Mn₄ Ca} oxygen evolving complex (OEC) in photosystem II was achieved. Under the conditions tested, all three GT-scaffolds were active molecular WOCs, with Co₉ and Co₂₀ outperforming the well-known Na₁₀ [Co₄ (H₂ O)₂ (PW₉ O₃₄ )₂ ] {Co₄ P₂ W₁₈ } by a factor of 2 as shown by a direct comparison of their turnover numbers (TONs). With TONs up to 159.9 and a turnover frequency of 0.608 s^-1 Co₉ currently represents the fastest Co-GT-based WOC, and photoluminescence emission spectroscopy provided insights into its photocatalytic WOC mechanism. Cyclic voltammetry, dynamic light scattering, UV/Vis and IR spectroscopy showed recyclability and integrity of the catalysts under the applied conditions. The experimental results were supported by computational studies, which highlighted that the facilitated oxidation of Co₉ was due to the higher energy of its highest occupied molecular orbital electrons as compared to Co₄ .

Defect {(WVIO7)WVI4} and Full {(WVIO7)WVI5} Pentagonal Units as Synthons for the Generation of Nanosized Main Group V Heteropolyoxotungstates

We report on the synthesis and characterization of three new nanosized main group V heteropolyoxotungstates K_xNa_y[H₂(XW^VI₉O₃₃)(W^VI₅O₁₂)(X₂W^VI₂₉O₁₀₃)]·nH₂O {X₃W₄₃} (x = 11, y = 16, and n = 115.5 for X = Sb^III; x = 20, y = 7, and n = 68 for X = Bi^III) and K₈Na₁₅[H₁₆(Co^II(H₂O)₂)_0.9(Co^II(H₂O)₃)₂(W^VI_3.1O₁₄)(Sb^IIIW^VI₉O₃₃)(Sb^III₂W^VI₃₀O₁₀₆)(H₂O)]·53H₂O {Co₃Sb₃W₄₂}. On the basis of the key parameters for the one-pot synthesis strategy of {Bi₃W₄₃}, a rational step-by-step approach was developed using the known Krebs-type polyoxotungstate (POT) K₁₂[Sb^V₂W^VI₂₂O₇₄(OH)₂]·27H₂O {Sb₂W₂₂} as a nonlacunary precursor leading to the synthesis and characterization of {Sb₃W₄₃} and {Co₃Sb₃W₄₂}. Solid-state characterization of the three new representatives {Bi₃W₄₃}, {Sb₃W₄₃}, and {Co₃Sb₃W₄₂} by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), and elemental analysis, along with characterization in solution by UV/vis spectroscopy shows that {Bi₃W₄₃}, {Sb₃W₄₃}, and {Co₃Sb₃W₄₂} represent the first main group V heteropolyoxotungstates encapsulating a defect {(W^VIO₇)W^VI₄} ({X₃W₄₃}, X = Bi^III and Sb^III) or full {(W^VIO₇)W^VI₅} ({Co₃Sb₃W₄₂}) pentagonal unit. With 43 tungsten metal centers, {X₃W₄₃} (X = Bi^III and Sb^III) are the largest unsubstituted tungstoantimonate– and bismuthate clusters reported to date. By using time-dependent UV/vis spectroscopy, the isostructural representatives {Sb₃W₄₃} and {Bi₃W₄₃} were subjected to a comprehensive study on their catalytic properties as homogeneous electron-transfer catalysts for the reduction of K₃[Fe^III(CN)₆] as a model substrate revealing up to 5.8 times higher substrate conversions in the first 240 min (35% for {Sb₃W₄₃}, 29% for {Bi₃W₄₃}) as compared to the uncatalyzed reaction (<6% without catalyst after 240 min) under otherwise identical conditions.

We report on the synthesis and characterization of three new tungsten-based defect {(W^VIO₇)W^VI₄}K_xNa_y[H₂(XW^VI₉O₃₃)(W^VI₅O₁₂)(X₂W^VI₂₉O₁₀₃)]·nH₂O {X₃W₄₃} (x = 11, y = 16, and n = 115.5 for X = Sb^III; x = 20, y = 7, and n = 68 for Bi^III) or full pentagonal {(W^VIO₇)W^VI₅} unit K₈Na₁₅[H₁₆(Co^II(H₂O)₂)_0.9(Co^II(H₂O)₃)₂(W^VI_3.1O₁₄)(Sb^IIIW^VI₉O₃₃)(Sb^III₂W^VI₃₀O₁₀₆)(H₂O)]·53H₂O {Co₃Sb₃W₄₂} encapsulating main group V representatives. With 43 W centers, {Sb₃W₄₃} and {Bi₃W₄₃} exhibit the highest nuclearity among unsubstituted tungstoantimonates and bismuthates reported to date. The catalytic properties of {Sb₃W₄₃} and {Bi₃W₄₃} as homogeneous electron-transfer catalysts for the reduction of K₃[Fe^III(CN)₆] to K₄[Fe^II(CN)₆] was investigated.

Keggin-type polyoxometalate 1 : 1 complexes of Pb(II) and Bi(III): experimental, theoretical and luminescence studies

Bi3+ and Pb2+ uptake by a monolacunary Keggin-type [PW11O39]7- anion leads to the formation of [PW11O39Bi]4- and [PW11O39Pb]5- complexes with a stereochemically active lone pair at the incorporated heterometal. The two complexes were isolated as (TBA)4[PW11O39Bi] (1) and (TBA)5[PW11O39Pb] (2) and characterized by 31P and 183W NMR spectroscopy, high-resolution electrospray mass-spectrometry (HR-ESI-MS) and cyclic voltammetry (CV). EXAFS and XANES data confirm the unchanged oxidation state and ψ-square pyramidal geometry of Bi3+ and Pb2+ in 1 and 2. DFT calculations were used in order to (i) confirm the absence of ligands attached to the heterometal sites in both complexes and localize the lone pair, and (ii) assign all signals in the 183W NMR spectra. Complexes 1 and 2 demonstrate photoluminescence (PL). A reversible change in the PL spectra of both complexes in the presence of water vapor has been detected. On the contrary, PL data for sandwich-type ((CH3)4N)4K3[H4(PW11O39)2Bi]·25H2O (3) do not show sensitivity to water vapor.

Synthesis, Characterization, and Phosphoesterase Activity of a Series of 4f- and 4d-Sandwich-Type Germanotungstates [(n-C4H9)4N]l/mH2[(M(H2O)3)(γ-GeW10O35)2] (M = CeIII, NdIII, GdIII, ErIII, l = 7; ZrIV, m = 6)

We report on a family of five new 4f- and 4d-doped sandwich-type germanotungstates with the general formula [(n-C₄H₉)₄N]_l/mH₂[(M(H₂O)₃)(γ-GeW₁₀O₃₅)₂]·3(CH₃)₂CO [M(H₂O)₃(GeW₁₀)₂] (M = Ce^III, Nd^III, Gd^III, Er^III, l = 7; Zr^IV, m = 6), which have been synthesized at room temperature in an acetone–water mixture. Among the compound series, [Zr(H₂O)₃(GeW₁₀)₂]^8–, which has been obtained in the presence of 30% H₂O₂, represents the first example of a 4d-substituted germanotungstate incorporating the intact dilacunary [γ-Ge^IVW₁₀O₃₆]^8– building block. All compounds were characterized thoroughly in the solid state by single-crystal and powder X-ray diffraction (XRD), IR spectroscopy, thermogravimetric analysis (TGA), and elemental analysis and in solution by NMR and UV–vis spectroscopy. The phosphoesterase activity of [Ce(H₂O)₃(GeW₁₀)₂]^9– and [Zr(H₂O)₃(GeW₁₀)₂]^8– toward the model substrates 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP) was monitored with ¹H- and ³¹P-NMR spectroscopy revealing an acceleration of the hydrolytic reaction by an order of magnitude (k_corr = 3.44 (±0.30) × 10^–4 min^–1 for [Ce(H₂O)₃(GeW₁₀)₂]^9– and k_corr = 5.36 (±0.05) × 10^–4 min^–1 for [Zr(H₂O)₃(GeW₁₀)₂]^8–) as compared to the uncatalyzed reaction (k_uncat = 2.60 (±0.10) × 10^–5 min^–1). [Ce(H₂O)₃(GeW₁₀)₂]^9– demonstrated improved antibacterial activity toward Moraxella catarrhalis (MIC 32 μg/mL), compared to the unsubstituted [GeW₁₀O₃₆]^8– POM (MIC 64 μg/mL).

We report on the synthesis and characterization of five new monosubstituted 4f- and 4d-germanotungstates [(n-C₄H₉)₄N]_l/mH₂[(M(H₂O)₃)(γ-GeW₁₀O₃₅)₂]·3(CH₃)₂CO [M(H₂O)₃(GeW₁₀)₂] (M = Ce^III, Nd^III, Gd^III, Er^III, l = 7; Zr^IV; m = 6). The phosphoesterase properties of [Ce(H₂O)₃(GeW₁₀)₂]⁹⁻ and [Zr(H₂O)₃(GeW₁₀)₂]⁸⁻ were investigated by probing the hydrolytic activity toward 4-nitrophenyl phosphate (NPP) and O,O-dimethyl O-(4-nitrophenyl) phosphate (DMNP). Antibacterial tests revealed inhibiting activity of [Ce(H₂O)₃(GeW₁₀)₂]⁹⁻ against Moraxella catarrhalis.

Selective Hydrolysis of Ovalbumin Promoted by Hf(IV)-Substituted Wells-Dawson-Type Polyoxometalate

The reactivity and selectivity of Wells-Dawson type polyoxometalate (POM), K₁₆[Hf(α₂-P₂W₁₇O₆₁)₂]·19H₂O (Hf1-WD2), have been examined with respect to the hydrolysis of ovalbumin (OVA), a storage protein consisting of 385 amino acids. The exact cleavage sites have been determined by Edman degradation experiments, which indicated that Hf1-WD2 POM selectively cleaved OVA at eight peptide bonds: Phe13-Asp14, Arg85-Asp86, Asn95-Asp96, Ala139-Asp140, Ser148-Trp149, Ala361-Asp362, Asp362-His363, and Pro364-Phe365. A combination of spectroscopic methods including ³¹P NMR, Circular Dichroism (CD), and Tryptophan (Trp) fluorescence spectroscopy were employed to gain better understanding of the observed selective cleavage and the underlying hydrolytic mechanism. ³¹P NMR spectra have shown that signals corresponding to Hf1-WD2 gradually broaden upon addition of OVA and completely disappear when the POM-protein molar ratio becomes 1:1, indicating formation of a large POM/protein complex. CD demonstrated that interactions of Hf1-WD2 with OVA in the solution do not result in protein unfolding or denaturation even upon adding an excess of POM. Trp fluorescence spectroscopy measurements revealed that the interaction of Hf1-WD2 with OVA (K_q = 1.1 × 10⁵ M⁻¹) is both quantitatively and qualitatively slightly weaker than the interaction of isostructural Zr-containing Wells-Dawson POM (Zr1-WD2) with human serum albumin (HAS) (K_q = 5.1 × 10⁵ M⁻¹).

Rare-Earth-Incorporated Tellurotungstate Hybrids Functionalized by 2-Picolinic Acid Ligands: Syntheses, Structures, and Properties

A series of organic-inorganic rare-earth-incorporated tellurotungstate hybrids, Na₄[RE₂(H₂O)₄(pica)₂W₂O₅][(RE(H₂O)W₂(Hpica)₂O₄)(B-β-TeW₈O₃₀H₂)₂]₂·38H₂O (RE = La^III (1), Ce^III (2), Nd^III (3), Sm^III (4), Eu^III (5); Hpica = 2-picolinic acid), were prepared via a one-step assembly reaction of Na₂WO₄·2H₂O, RE(NO₃)₃·6H₂O, K₂TeO₃, Hpica, and triethylamine (tea). Notably, the solubilization of tea toward Hpica and the solubilization of Hpica toward RE cations in the reaction system play an important role in the formation of 1-5. The most significant feature of 1-5 consists of an intriguing tetrameric [RE₂(H₂O)₄(pica)₂W₂O₅][(RE(H₂O)W₂(Hpica)₂O₄)(B-β-TeW₈O₃₀H₂)₂]₂^4- polyoxoanion constructed from two tetravacant Keggin sandwich-type [(RE(H₂O)W₂(Hpica)₂O₄)(B-β-TeW₈O₃₀H₂)₂]^5- entities linked by a RE-W-Hpica {RE₂(H₂O)₄(pica)₂W₂O₅}⁶⁺ cluster, in which Hpica ligands not only play a key bridging role in linking RE and W centers by carboxylic groups in an irregular N-O-RE-O-W-O six-membered-ring motif but also can directly chelate with W centers via N and O atoms in a stable N-O-C-O-W five-membered-ring fashion. 1-5 represent rare organic-inorganic hybrid RE-substituted tellurotungstates. Moreover, the solid-state photoluminescence properties of 3-5 have been deeply investigated, and these compounds exhibit the characteristic emission stemming from intra-4f transitions of RE ions. The energy transfer of the O → W transitions sensitizing the emission of Sm^III centers in 4 is convincingly proved by time-resolved emission spectra (TRES); the increase in the strongest typical emission of Sm^III ions at a decay time of 17 μs is accompanied by the decline of O → W emission, and the CIE 1931 diagram was obtained from the corresponding TRES. Furthermore, a comparison of the luminescence behaviors of 5 in the solid state and in solution reveals the structural skeletal integrity of 5 in solution and a shorter decay lifetime in the solution caused by the high-frequency O-H oscillators.