Lacunary Polyoxometalate Research Articles

Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO2 Reduction Activity.

The syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox-active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally-new lacunary POM-stabilized Ag clusters, TBA6 H14 Ag14 (DPPB)4 (CH3 CN)9 [Ag24 (Si2 W18 O66 )3 ] ⋅ 10CH3 CN ⋅ 9H2 O ({Ag24 (Si2 W18 O66 )3 }, TBA=tetra-n-butylammonium, DPPB=1,4-Bis(diphenylphosphino)butane) and TBA14 H6 Ag9 Na2 (H2 O)9 [Ag27 (Si2 W18 O66 )3 ] ⋅ 8CH3 CN ⋅ 10H2 O ({Ag27 (Si2 W18 O66 )3 }), using a facile one-pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM-stabilized Ag clusters could be readily tuned by the addition of different organic ligands. In both compounds, the central trefoil-propeller-shaped {Ag24 }14+ and {Ag27 }17+ clusters bearing 10 delocalized valence electrons are stabilized by three C-shaped {Si2 W18 O66 } units. The femtosecond/nanosecond transient absorption spectroscopy revealed the rapid charge transfer between {Ag24 }14+ core and {Si2 W18 O66 } ligands. Both compounds have been pioneeringly investigated as catalysts for photocatalytic CO2 reduction to HCOOH with a high selectivity.

Atomically Precise Silver Clusters Stabilized by Lacunary Polyoxometalates with Photocatalytic CO2 Reduction Activity

AbstractThe syntheses of atomically precise silver (Ag) clusters stabilized by multidentate lacunary polyoxometalate (POM) ligands have been emerging as a promising but challenging research direction, the combination of redox‐active POM ligands and silver clusters will render them unexpected geometric structures and catalytic properties. Herein, we report the successful construction of two structurally‐new lacunary POM‐stabilized Ag clusters, TBA6H14Ag14(DPPB)4(CH3CN)9[Ag24(Si2W18O66)3] ⋅ 10CH3CN ⋅ 9H2O ({Ag24(Si2W18O66)3}, TBA=tetra‐n‐butylammonium, DPPB=1,4‐Bis(diphenylphosphino)butane) and TBA14H6Ag9Na2(H2O)9[Ag27(Si2W18O66)3] ⋅ 8CH3CN ⋅ 10H2O ({Ag27(Si2W18O66)3}), using a facile one‐pot solvothermal approach. Under otherwise identical synthetic conditions, the molecular structures of two POM‐stabilized Ag clusters could be readily tuned by the addition of different organic ligands. In both compounds, the central trefoil‐propeller‐shaped {Ag24}14+ and {Ag27}17+ clusters bearing 10 delocalized valence electrons are stabilized by three C‐shaped {Si2W18O66} units. The femtosecond/nanosecond transient absorption spectroscopy revealed the rapid charge transfer between {Ag24}14+ core and {Si2W18O66} ligands. Both compounds have been pioneeringly investigated as catalysts for photocatalytic CO2 reduction to HCOOH with a high selectivity.

A novel ligand protection strategy based on lacunary polyoxometalate to precisely construct CoMoS active sites for hydrodesulfurization

Efficient CoMoS catalysts with intimate bimetallic synergy are derived from cobalt-substituted phosphomolybdate and exhibited excellent hydrodesulfurization (HDS) activity. Based on ligand protection strategy, the introduction of pyridine ligands onto the vacancies of the trivacant polyoxometalates (POMs) successfully overcame their low stability and isomerization behavior in solution. Subsequently, Co2+ was anchored in the molecular skeleton of [A-α-PMo9O31(py)3]3− (PMo9-py) to form CoxPMo9-py precursors with high Co/Mo ratios, which enhanced the reducibility of Mo species and transformed them to abundant CoMoS active phase during sulfidation process. The quenching effect of pyridine molecules on the acidic sites of support and carbon deposition generated in the high temperature sulfidation weakened the strong metal-support interactions (SMSI) while improving the dispersion and sulfidation of active metals. Due to the unique structure of CoxPMo9-py, the CoMoS phase with high dispersion, efficient synergy and high concentration was obtained. The combination of POMs precursors and pyridine ligands enabled the S-CoxPMo9-py/Al2O3 catalyst to achieve up to 99.5% conversion of dibenzothiophene (DBT).

Bioactivity of Nanohybrid: Comprising of Metallosalen Incorporated into Lacunary Polyoxometalate and Encapsulated with Chitosan Biopolymer

Biocompatible polymer chitosan has note-worthy applications in biomedical science. Nanohybrids synthesized by using chitosan as an encapsulating unit for polyoxometalates (POMs) and study of its biomedical applications is a fast-emerging field. In this research work, a lacunary polyoxometalate (α-K8SiW11O39) has been synthesized and then alkylsilane has been inserted into its lacunary position. It has been then reacted with 2-hydroxy-1-naphtaldehyde followed by copper metalation and finally encapsulated into chitosan by using the ionotropic gelation technique, in which the chitosan and the POM served as cation and anion, respectively. The bands in UV-Vis spectra at characteristic wavelength indicate that the organosilane is successfully inserted into α-K8SiW11O39 and metalled with Cu. Then its encapsulation into chitosan to synthesize final nanohybrid has been confirmed by UV-Vis spectra. Further, chitosan, POM inserted with organosilane and nanohybrid have been characterized by FT-IR. EDX analysis reveals the presence of all the expected elements in their desired ratios. EDX study was further supported by Inductively Coupled Plasma (ICP) technique. Morphology of nanohybrid has been studied by Scanning Electron Microscope (SEM) imaging. The loading and entrapment efficiency of the prepared nanohybrid was exceptionally excellent and was calculated to be 81.2% and 59.1%, respectively. In vitro drug release study suggested sustainable and pH-modulated release behaviour of the nanohybrid. Further, it is the first time that an organosilane attached to lacunary POM, then metalated with Cu and finally encapsulated into CS has been investigated for drug delivery. The antibacterial activity of POM inserted with organosilane and nanohybrid have been tested against bacterial strains of B. subtilis gram (+)ve and E. coli gram (-)ve. The antibacterial activity of nanohybrid has been improved as compared to bare POM inserted with metallated organosilane and chitosan.

Cr(III)-complex tethered lacunary polyoxometalate as an efficient electrocatalyst for hydrogen evolution reaction in aqueous media

A lacunary polyoxometalate-based hybrid material, wherein Cr (acac)3 complex is covalently tethered through aminopropyltrimethoxysilyl groups to a Keggin-type lacunary phosphomolybdate anion, [PMo11O39]7-, is reported as a new heterogeneous electrocatalyst for the efficient electrocatalytic hydrogen evolution process. Physicochemical characterization techniques, like FT-IR spectroscopy, X-ray diffraction (XRD), and energy dispersive X-ray (EDX) analyses confirmed the successful functionalization and synthesis of desired material. The prepared hybrid material revealed eminent hydrogen evolution activity with a low overpotential of 330 mV to attain a 10 mA cm−2 current density and a Tafel slope of 150 mV.dec−1. Additionally, it also exhibited outstanding electrochemical stability in H2SO4 (0.5 M) over 8 h and catalytic activity retention even after 2000 catalytic cycles. This work introduces an appropriate procedure for preparing inexpensive and highly active electrocatalysts for replacing precious Pt counterparts in hydrogen evolution process.

Recent advances in polyoxometalate-based lanthanide–oxo clusters

Polyoxometalate (POM)-based lanthanide-oxo clusters (LnOCs) are a class of polynuclear lanthanide–oxygen complexes formed by polyoxometalate stabilization through oxygen bridges in which POMs can be viewed as multidentate inorganic ligands. POM-based LnOCs have received interest owing to their interesting structures and potential applications. In this paper, we summarize the classification, synthesis strategies, and properties of POM-based LnOCs. POM-based LnOCs are classified into three main categories according to their metal core element type and quantity: pure 4f clusters, 5d–4f clusters, and 3d–4f clusters. Their synthetic strategies are divided into four categories based on the source of the POM involved in the structural assembly: the lacunary POMs ligand-directed method, the in-situ transformation of lacunary POMs ligand-directed method, the in-situ generation of lacunary POMs ligand-directed method, and mixed synthesis strategies. In addition, the single-molecule magnets of POM-based LnOCs and their proton conduction properties are summarized.

Lacunary polyoxometalate oriented construction of dispersed Ni3S2 confined in WO3 for electrocatalytic water splitting

Manufacturing low-cost, high-performance and earth-rich catalysts for hydrogen evolution (HER) and oxygen evolution reactions (OER) is critical to achieving sustainable green hydrogen production. Herein, we utilize lacunary Keggin-structure [PW9O34]9− (PW9) as a molecular pre-assembly platform to anchor Ni within a single PW9 molecule by vacancy-directed and nucleophile-induced effects for the uniform dispersion of Ni at the atomic level. The chemical coordination of Ni with PW9 can avoid the aggregation of Ni and favor the exposure of active sites. The Ni3S2 confined by WO3 prepared from controlled sulfidation of Ni6PW9/Nickel Foam (Ni6PW9/NF) exhibited excellent catalytic activity in both 0.5 M H2SO4 and 1 M KOH solutions, which required only 86 mV and 107 mV overpotentials for HER at a current density of 10 mA∙cm−2 and 370 mV for OER at 200 mA∙cm−2. This is attributed to the good dispersion of Ni at the atomic level induced by trivacant PW9 and the enhanced intrinsic activity by synergistic effect of Ni and W. Therefore, the construction of active phase from the atomic level is insightful to the rational design of dispersed and efficient electrolytic catalysts.

Flowing scalable production of sulfenamides by active site-tuned lacunary polyoxometalate foams

Four transition-metal lacunary polyoxometalates (TM-LPOMs, TM = Cu, Co, Ni, and Mn) are prepared and fabricated into ultralow density LPOM-based foams (LPOMs@CMC) for the efficient flowing catalytic production of sulfenamide additives.

Boosting Simultaneous Uranium Decorporation and Reactive Oxygen Species Scavenging Efficiency by Lacunary Polyoxometalates.

The chemical toxicity and the oxidative stress induced by the internal exposure of uranium is responsible for the long-term adverse effect of in vivo contamination of uranium. An agent with simultaneous removal capability of uranium and excess reactive oxygen species (ROS) is highly desired. Herein, the lacunary Keggin-type polyoxometalate (POM) is demonstrated to selectively bind with uranyl ions in the presence of excess essential divalent ions and exhibits a compelling ROS scavenging efficiency of 78.8%. In vivo uranium decorporation assays illustrate the uranium sequestration efficiencies of 74.0%, 49.4%, and 37.1% from kidneys by prophylactic, prompt, and delayed administration of lacunary POM solution, respectively. The superior ROS quenching and uranium removal performance in comparison with all reported bifunctional agents endow lacunary polyoxometalates as novel agents to effectively protect people from injuries caused by the internal exposure of actinides.

Creation of Highly Dispersed Supported Polyoxometalate Cesium Salts via Cation Exchange from Alkylammonium Salts on Supports

AbstractWe have reported several precisely designed metal‐oxo clusters on lacunary polyoxometalate (POM) tetra‐n‐butylammonium (TBA) salts in organic solvents. However, owing to their low thermostability and/or low effective surface area, POM TBA salts are not amenable to heterogeneous catalysts for gas‐phase reactions at high temperature. To avoid this problem, we developed a new preparation method that obtains highly dispersed supported‐POM Cs salts (Cs−POM/support) via cation exchange from the corresponding TBA salts on supports. In this study, a model Keggin‐type POM called TBA4PVMo11O40 (TBA−PVMo11) is supported on oxides (TBA−PVMo11/support) using an incipient wetness method in acetonitrile. This TBA−PVMo11/support was cation‐exchanged with cesium trifluoromethanesulfonate in ethanol to obtain supported‐POM Cs salts (Cs−PVMo11/support). Various characterizations revealed that the TBA−PVMo11/support maintained the original Keggin structure during cation exchange and that Cs−PVMo11 was highly dispersed on the supports. Furthermore, Cs−PVMo11/support maintained the Keggin structure even after calcination at 573 K under an aerobic condition.

A Lacunary Polyoxometalate Anion Tightly Sealed in a ZIF‐8 Polyhedron with Ultrafast Cationic Dye Adsorption

AbstractFinding efficient materials for treatment of dye wastewater is a hot research topic in the field of environmental science. In this paper, the mono‐lacunary polyoxometalate anion (SiW11) is completely sealed in a zeolitic imidazolate (ZIF‐8) polyhedron, forming a new polyhedral absorbent, SiW11@ZIF‐8, with an intact surface and a negative charge center. Unlike saturated Keggin type polyoxoanions, SiW11is only stable under neutral conditions and does not release any protons in solutions. Therefore, SiW11@ZIF‐8 does not display the usually observed acid‐induced etching and shows effective and ultrafast adsorption for the cationic dye methylene blue. This work not only indicates that the neutral polyoxoanion is a more suitable candidate to be sealed in ZIF‐8 to form a stable unpunched composite, but also provides a new concept for the design of stable polyoxometalate@ZIF adsorbents to be potentially used in the treatment of cationic dyes in wastewater.

Ultralow-Loading and High-Performing Ionic Liquid-Immobilizing Rhodium Single-Atom Catalysts for Hydroformylation.

We have developed a Keggin polyoxometalate (POM)-based ionic-liquid (IL)-immobilizing rhodium single-atom Rh catalyst (MTOA)5 [SiW11 O39 Rh] (MOTA=methyltrioctylammonium cation) that can afford exceptionally high catalytic activity for the hydroformylation of alkenes to produce aldehydes at an ultralow loading of Rh (ca. 3 ppm). For styrene hydroformylation, both the conversion and the yield of the aldehyde can reach almost 99 %, and a TOF as high as 9000 h-1 was obtained without using any phosphine ligand in the reaction process. Further characterization by FTIR, ICP and ESI-MS analysis revealed that the single Rh atom was incorporated in the lacunary POM anions. In particular, the bulky IL cation can play an additional role in stabilizing Rh species and thus prevent aggregation and leaching of Rh species. The IL catalyst was miscible with n-hexane at temperatures; this contributed to exceptionally high activity for hydroformylation even at ultra-low loading of IL catalyst.

Controlled synthesis of efficient NiWS active phases derived from lacunary polyoxometalate and the application in hydrodesulfurization

Efficient catalysts with abundant NiWS active phases for hydrodesulfurization (HDS) were prepared based on structural diversity as well as unique electrostatics property of lacunary Keggin polyoxometalates (POMs). Owing to super nucleophilicity and coordinative ability, the trivacant Keggin [PW9O34]9- (PW9) can accurately capture and anchor Ni2+ promoters into its skeleton to form nanosized Nix@PW9 molecule in impregnating solution, thereby achieving ultra-dispersion of Ni promoters, high Ni/W ratio, and atomic-scale Ni–W proximity. The superior structure of Nix@PW9 promoted the simultaneous reduction and sulfuration of Ni and W species, thus obtaining shorter slab length, less stacking number, highly efficient synergism, and high concentration of NiWS active phases. Therefore, the resulted S-NiPW9/Al2O3 catalyst exhibits efficient HDS activity for dibenzothiophene (DBT) removal compared to that of reference catalysts prepared from monovacant [PW11O39]7- (PW11), saturated [PW12O40]3- (PW12), and conventional oxide precursors. The structure-directing effects of oxidic POM precursors on the texture and performance of HDS active phases were revealed by employing a variety of characterization methods, including transmission Fourier transform infrared (TS-FTIR), attenuated total reflectance Fourier transform infrared (ATR-FTIR), ultraviolet–visible spectroscopy (UV–Vis), single crystal X-ray diffraction, H2 temperature programmed reduction (H2-TPR), CO adsorbed Fourier transform infrared spectroscopy (IR/CO), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). This POMs-based molecular methodology opens a new avenue to better understand the evolution behavior of precursors and the formation mechanism of active species during the preparation of catalysts.

Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands.

The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW11O39]8– anion affords a series of isostructural compounds, namely, K5[LnIII(α-SiW11O39)(C20H22Br2N2O4)]·14H2O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the LnIII ion in a biaugmented trigonal prismatic geometry, which occupies the external O4 site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N2O2 coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ∼5–6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.

Functionalized polyoxometalate microspheres ensure selective adsorption of phosphoproteins and glycoproteins.

Lacunary polyoxometalate (POM), [PW9O34]9-, grafts with a boronic acid group attached via an organosilane bridge assemble into microspheres, PW9-Si-APBA. The oxygen-rich and hydrophilic surface of POM facilitates the binding of phosphate groups in phosphoproteins and glycans in glycoproteins. While the metal-oxo in POM provides π-π interactions with the phosphate groups of phosphoproteins, the boronic acid group specifically binds to glycoproteins via the cis-diols of glycans. Therefore, these multi-driving forces ensure the selective adsorption of phosphoproteins and glycoproteins by PW9-Si-APBA microspheres in biological sample matrixes, even in the presence of very high protein abundance, i.e., BSA, at mass ratio of β-ca/IgG/OVA/BSA = 1 : 1 : 1 : 200.

PH-controlled construction of lanthanide clusters from lacunary polyoxometalate with single-molecule magnet behavior

Six lanthanide clusters were synthesized via pH-controlled strategy: Na18[Ln4(Sb3O2)2(SbW10O37)2(SbW8O31)2(H2O)6]·(H2O)60 [Ln = Dy3+ (1), Ho3+ (2), Er3+ (3)] in pH 5.5 NaAc-HAc buffer solution displaying tetrameric architectures, and Na23[Ln3(SbW9O33)3(CH3COO)3(WO4)(H2O)3]·(H2O)50 [Ln = Dy3+ (4), Ho3+ (5), Er3+ (6)] in pH 7.2 NaAc/HAc solution featuring trimeric aggregates. Obviously, pH-controlled strategy can design the structures of lanthanide clusters. Moreover, the ac magnetic susceptibilities proved that compounds 1 and 4 manifested apparent slow magnetic relaxation behaviors. Interestingly, compound 1 exhibited both temperature- and frequency-dependent in-phase (χ′) and out-of-phase (χ″) ac signals, behaving as a zero-field SMM with Ueff = 46.8 K, τ0 = 8.11 × 10−7 s calculated on the basis of Orbach process, and Ueff = 58.2 K, τ0 = 3.63 × 10−7 s according to Raman and Orbach relaxation processes. Compound 4 was found to be a SMM with a fast QTM, yielding a reversal barrier Ueff = 1.12 K with τ0 = 9.27 × 10−6 s.

Removal of Multiple Contaminants from Water by Polyoxometalate Supported Ionic Liquid Phases (POM-SILPs).

The simultaneous removal of organic, inorganic, and microbial contaminants from water by one material offers significant advantages when fast, facile, and robust water purification is required. Herein, we present a supported ionic liquid phase (SILP) composite where each component targets a specific type of water contaminant: a polyoxometalate-ionic liquid (POM-IL) is immobilized on porous silica, giving the heterogeneous SILP. The water-insoluble POM-IL is composed of antimicrobial alkylammonium cations and lacunary polyoxometalate anions with heavy-metal binding sites. The lipophilicity of the POM-IL enables adsorption of organic contaminants. The silica support can bind radionuclides. Using the POM-SILP in filtration columns enables one-step multi-contaminant water purification. The results show how multi-functional POM-SILPs can be designed for advanced purification applications.

Synthesis and Characterization of 0D-3D Copper-Containing Tungstobismuthates Obtained from the Lacunary Precursor Na9[B-α-BiW9O33

The reaction of the lacunary polyoxometalate precursor Na9[B-α-BiW9O33]·19.5H2O with Cu(II) ions was explored in search of new economic ways to copper tungstobismuthates as interesting prototypes for water oxidation and reduction catalysts. The emerging series of new 0D-3D polyoxometalate architectures with distinct copper cores was structurally characterized. Na6Rb6[Cu3(H2O)3(BiW9O33)2] (Cu-4) and 3D-K6.56Cu0.43H2.20[(Cu3Cl)(K2.62Cu0.38(H2O)3)(B-α-BiW9O33)2]·13H2O (Cu-5) display a Cu3(H2O)3 core. The 2D representatives Na12[Cu2(H2O)4Cl2(BiW10O35)2] (Cu-1a), Na10[Cu2(H2O)6(BiW10O35)2] (Cu-1b), 2D-Na7K3Cu0.5Cl[Cu2(H2O)4(BiW10O35)2] (Cu-2), and 2D-Na5.5K2.5Cu[Cu2(H2O)4(BiW10O35)2] (Cu-3) contain Cu2(H2O)nW2O4 cores. Interestingly, the bismuth-free 1D paratungstate B Na4K4Cu[H2W12O42] (Cu-6) is formed through reassembly of the precursor. Cu-5 displays a disordered transition metal core, implying the presence of the polyanions [Cu4(H2O)4(BiW9O33)2]10- and [Cu5(H2O)5(BiW9O33)2]8-. The magnetic properties of Cu-5 as well as its activity as visible-light-driven H2 and O2 evolution catalyst were evaluated.

Synthesis and Disassembly/Reassembly of Giant Ring-Shaped Polyoxotungstate Oligomers.

The disassembly and reassembly of giant molecules are essential processes in controlling the structure and function of biological and artificial systems. In this work, the disassembly and reassembly of a giant ring-shaped polyoxometalate (POM) without isomerization of the monomeric units is reported. The reaction of a hexavacant lacunary POM that is soluble in organic solvents, [P2 W12 O48 ](14-) , with manganese cations gave the giant ring-shaped POM [{γ-P2 W12 O48 Mn4 (C5 H7 O2 )2 (CH3 CO2 )}6 ](42-) . This POM is a hexamer of manganese-substituted {P2 W12 O48 Mn4 } units, and its inner cavity was larger than any of those previously reported for ring-shaped polyoxotungstates. It was disassembled into monomeric units in acetonitrile, and the removal of the capping organic ligands on the manganese cations led to reassembly into a tetrameric ring-shaped POM, [{γ-P2 W12 O48 Mn4 (H2 O)6 }4 (H2 O)4 ](24-) .

Synthesis and Disassembly/Reassembly of Giant Ring‐Shaped Polyoxotungstate Oligomers

AbstractThe disassembly and reassembly of giant molecules are essential processes in controlling the structure and function of biological and artificial systems. In this work, the disassembly and reassembly of a giant ring‐shaped polyoxometalate (POM) without isomerization of the monomeric units is reported. The reaction of a hexavacant lacunary POM that is soluble in organic solvents, [P2W12O48]14−, with manganese cations gave the giant ring‐shaped POM [{γ‐P2W12O48Mn4(C5H7O2)2(CH3CO2)}6]42−. This POM is a hexamer of manganese‐substituted {P2W12O48Mn4} units, and its inner cavity was larger than any of those previously reported for ring‐shaped polyoxotungstates. It was disassembled into monomeric units in acetonitrile, and the removal of the capping organic ligands on the manganese cations led to reassembly into a tetrameric ring‐shaped POM, [{γ‐P2W12O48Mn4(H2O)6}4(H2O)4]24−.