A {Nb6P2W12}‐Based Hexameric Manganese Cluster with Single‐Molecule Magnet Properties

By deliberately using a metastable polyanion [(NbO₂)₆P₂W₁₂O₅₆]^12? ( 1 ), which was formed in situ, we have discovered the unprecedented hexameric cluster {Mn₁₅(Nb₆P₂W₁₂O₆₂)₆} ( 2 ), in which the six polyanions [Nb₆P₂W₁₂O₆₁]^10? are alternately connected by four intriguing trinuclear {Mn^III₃} moieties and four {Mn^II} linkers. This discovery is the first in which the phosphoniobotungstate has been made accessible by using transition‐metal ions; furthermore, polyanion 2 represents the largest niobotungstate cluster reported to date. Analysis by means of electrospray ionization mass spectrometry (ESI‐MS ) provides insight into the self‐assembly process, and the peaks observed relate to the different charge states of the parent cluster, thus confirming the stability of 2 . In addition, magnetic‐susceptibility measurements reveal that each {Mn^III₃} subunit is a separate single‐molecule magnet (SMM). This discovery results from the exploration of the reverse effect of metastable polyanion 1 possessing high reactivity, thereby turning a disadvantage into an advantage. This finding could define a new synthetic strategy for the design and synthesis of magnetic polyoxometalate (POM) clusters.     

Self‐Templating and In Situ Assembly of a Cubic Cluster‐of‐Clusters Architecture Based on a {Mo24Fe12} Inorganic Macrocycle

Engineering self‐templating inorganic architectures is critical for the development of bottom‐up approaches to nanoscience, but systems with a hierarchy of templates are elusive. Herein we describe that the cluster‐anion‐templated (CAT) assembly of a {CAT}?{Mo₂₄Fe₁₂} macrocycle forms a giant ca. 220 nm³ unit cell containing 16 macrocycles clustered into eight face‐shared tetrahedral cluster‐of‐clusters assemblies. We show that {CAT}?{Mo₂₄Fe₁₂} with different CATs gives the compounds 1 – 4 for CAT=Anderson {FeMo₆} ( 1 ), Keggin {PMo₁₂} ( 2 ), Dawson {P₂W₁₈} ( 3 ), and {Mo₁₂O₃₆(HPO₃)₂} ( 4 ) polyoxometalates. “Template‐free” assembly can be achieved, whereby the macrocycle components can also form a template in situ allowing template to macrocycle to superstructure formation and the ability to exchange the templates. Furthermore, the transformation of template clusters within the inorganic macrocycle {Mo₂₄Fe₁₂} allows the self‐generation of an uncapped {Mo₁₂O₃₆(HPO₃)₂} in compound 4 .     

Assembly of Tungsten‐Oxide‐Based Pentagonal Motifs in Solution Leads to Nanoscale {W48}, {W56}, and {W92} Polyoxometalate Clusters

We report an approach to synthesize molecular tungsten‐oxide‐based pentagonal building blocks, in a new {W₂₁O₇₂} unit, and show how this leads to a family of gigantic molecular architectures including [H₁₂W₄₈O₁₆₄]^28? {W₄₈}, [H₂₀W₅₆O₁₉₀]^24? {W₅₆}, and [H₁₂W₉₂O₃₁₁]^58? {W₉₂}. The {W₄₈} and {W₅₆} clusters are both dimeric species incorporating two {W₂₁} units and the {W₅₆} species is the first example of a molecular metal oxide cluster containing a chiral “double‐stranded” motif which is stable in solution as confirmed by mass spectrometry. The {W₉₂} anion having four {W₂₁} units is one of the largest transition metal substituted isopolyoxotungstates known.     

Discovery of Heteroatom‐“Embedded” Te⊂{W18O54} Nanofunctional Polyoxometalates by Use of Cryospray Mass Spectrometry

The cryo game : Heteroatom‐embedded nanofunctional clusters are described that incorporate a [Te^VIO₆]^6? species contained within a {W₁₈O₅₄} cage. Not only does the tellurium‐based species activate the {W₁₈O₅₄} cluster surface for assembly of larger nanoscale structures, such as [H₁₀Te^VI₂W₅₈O₁₉₈]^26?, it also undergoes a redox transformation inside the cluster from [Te^VIO₆]^6? to [Te^IVO₃]^2?.

     

Unprecedented Selenium and Lanthanide Simultaneously Bridging Selenotungstate Aggregates Stabilized by Four Tetra‐vacant Dawson‐like {Se2W14} Units

In the presence of the larger [H₂N(CH₃)₂]⁺ and K⁺ counter cations as structure‐stabilizing agents, a class of unprecedented selenium and lanthanide (Ln) simultaneously bridging tetra‐vacant Dawson‐like selenotungstate aggregates [H₂N(CH₃)₂]₂Na₉K₂H₁₉{[Ln₄W₄ Se₄O₂₂(H₂O)₅](Se₂W₁₄O₅₂)₂}₂ ⋅ 60 H₂O [Ln=Tb^III ( 1 ), Dy^III ( 2 ), Ho^III ( 3 ), Er^III ( 4 ), Tm^III ( 5 ), Yb^III ( 6 )] have been obtained by the one‐pot assembly reaction of Na₂WO₄ ⋅ 2 H₂O, Ln(NO₃)₃ ⋅ 6 H₂O, and Na₂SeO₃ under moderately acidic aqueous conditions and the complexes were structurally characterized by elemental analyses, IR spectra, single‐crystal X‐ray diffraction, powder X‐ray diffraction (PXRD), and thermogravimetric (TG) analyses. It should be noted that the appropriate molar ratio of Se/W is extremely important in the formation of 1 – 6 and can effectively ameliorate the yield of 1 – 6 . Moreover, dimethylamine hydrochloride is also indispensable and plays a considerably important role in improving the solubility of Ln ions and stabilizing the structures of 1 – 6 . The main polyoxoanion skeletons of 1 – 6 are constructed from two sandwich‐type tetra‐vacant Dawson‐like {[Ln₄W₄Se₄O₂₂(H₂O)₅](Se₂W₁₄O₅₂)₂}¹⁶⁻ half‐units linked through two W‐O‐Ln bridges. The sandwich‐type half‐unit comprises two tetra‐vacant Dawson‐like [Se₂W₁₄O₅₂]¹²⁻ fragments encapsulating a unique dodecanuclear Se‐Ln‐W [Ln₄W₄Se₄O₂₂(H₂O)₅]⁸⁺ oxo cluster. Their solid‐state visible and NIR fluorescent properties and lifetime decay behaviors were measured and their solid‐state luminescent spectra mainly demonstrate the characteristic emission bands of Ln³⁺ ions. Moreover, the dominant wavelengths, the color purity, and correlated color temperatures of 1 – 5 have been also calculated. In addition, the luminous flux values of 1 – 5 are 2031, 6992, 3071, 921, and 477 lumen, respectively.     

New Perspectives for Old Clusters: Anderson–Evans Anions as Building Blocks of Large Polyoxometalate Frameworks in a Series of Heterometallic 3 d–4 f Species

A series of nine [Sb₇W₃₆O₁₃₃Ln₃M₂(OAc)(H₂O)₈]^17? heterometallic anions ( Ln₃M₂ ; Ln=La–Gd, M=Co; Ln=Ce, M=Ni and Zn) have been obtained by reacting 3 d metal disubstituted Krebs‐type tungstoantimonates(III) with early lanthanides. Their unique tetrameric structure contains a novel {MW₉O₃₃} capping unit formed by a planar {MW₆O₂₄} fragment to which three {WO₂} groups are condensed to form a tungstate skeleton identical to that of a hypothetical trilacunary derivative of the ?‐Keggin cluster. It is shown, for the first time, that classical Anderson–Evans {MW₆O₂₄} anions can act as building blocks to construct purely inorganic large frameworks. Unprecedented reactivity in the outer ring of these disk‐shaped species is also revealed. The Ln₃M₂ anions possess chirality owing to a {Sb₄O₄} cluster being encapsulated in left‐ or right‐handed orientations. Their ability to self‐associate in blackberry‐type vesicles in solution has been assessed for the Ce₃Co₂ derivative.     

Supramolecular Structures of Titanium(IV)‐Substituted Wells–Dawson Polyoxotungstates

The novel, dimeric titanium(IV )‐substituted phosphotungstate [(TiP₂W₁₅O₅₅OH)₂]^14? ( 1 ) has been synthesized and characterized by IR and ³¹P NMR spectroscopy, elemental analysis, and single‐crystal Xray diffraction. The polyanion consists of two [P₂W₁₅O₅₆]^12? Wells–Dawson moieties linked through two titanium(IV ) centers. Polyanion 1 is a dilacunary species and represents the first Ti‐containing sandwich‐type structure. The titanium centers are octahedrally coordinated by three oxygen atoms of each P₂W₁₅O₅₆ subunit. The edge‐shared TiO₆ units are symmetrically equivalent and have no terminal ligands. Polyanion 1 shows a chiral distortion within each P₂W₁₅Ti fragment. We also report on the structural characterization of the tetrameric, supramolecular species [{Ti₃P₂W₁₅O_57.5(OH)₃}₄]^24? ( 2 ). Polyanion 2 is composed of four equivalent P₂W₁₅Ti₃ fragments, fused together through terminal Ti? O bonds, leading to a structure with T_d symmetry.     

Time‐Resolved Assembly of Cluster‐in‐Cluster {Ag12}‐in‐{W76} Polyoxometalates under Supramolecular Control

We report the time‐resolved supramolecular assembly of a series of nanoscale polyoxometalate clusters (from the same one‐pot reaction) of the form: [H_(10+m)Ag₁₈Cl(Te₃W₃₈O₁₃₄)₂]_n, where n=1 and m=0 for compound 1 (after 4 days), n=2 and m=3 for compound 2 (after 10 days), and n=∞ and m=5 for compound 3 (after 14 days). The reaction is based upon the self‐organization of two {Te₃W₃₈} units around a single chloride template and the formation of a {Ag₁₂} cluster, giving a {Ag₁₂}‐in‐{W₇₆} cluster‐in‐cluster in compound 1 , which further aggregates to cluster compounds 2 and 3 by supramolecular Ag‐POM interactions. The proposed mechanism for the formation of the clusters has been studied by ESI‐MS. Further, control experiments demonstrate the crucial role that TeO₃^2?, Cl^?, and Ag⁺ play in the self‐assembly of compounds 1 – 3 .     

Dinuclear vanadium and tetranuclear iron complexes obtained with the open Wells–Dawson [Si2W18O66] tungstosilicate

Reaction of two transition metal cations M (M = V^V, Fe^III) on the open Wells–Dawson anion α-[{K(H₂O)₂}Si₂W₁₈O₆₆]^15– leads to dinuclear and tetranuclear complexes, respectively. The molecular anions [{KV₂O₃(H₂O)₂}(Si₂W₁₈O₆₆)]^11– and [{Fe₄(OH)₆}(Si₂W₁₈O₆₆)]^10– have been structurally characterized by single crystal X-ray diffraction. The oxo/hydroxometallic clusters [KV₂O₃(H₂O)₂]⁵⁺ and [Fe₄(OH)₆]⁶⁺ are included in the pocket between the two subunits of [Si₂W₁₈O₆₆]^16–. The Fe^III atoms of the iron complex can be reduced to Fe^II by a single four-electron step. To cite this article: N. Leclerc-Laronze et al., C. R. Chimie 9 (2006).     

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, {[W₁₄Ce^IV₆O₆₁]([W₃Bi₆Ce^III₃(H₂O)₃O₁₄][B‐α‐BiW₉O₃₃]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‐BiW₉O₃₃]^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.     

A {Co4O4} Cubane Incorporated within a Polyoxoniobate Cluster

A novel octacobalt‐containing polyoxoniobate, Na₆K₁₂[H₂Co₈O₄(Nb₆O₁₉)₄]?39 H₂O, has been prepared by a combination of hydrothermal and diffusion methods. The polyanion [H₂Co₈O₄(Nb₆O₁₉)₄]^18? incorporates a tetrameric assembly of Lindqvist‐type [Nb₆O₁₉]^8? fragments trapping a {Co^II₄Co^III₄} cluster which comprises a central {Co^III₄O₄} cubane core, surrounded by another four Co^II ions linkers. Furthermore, magnetic measurements show that the compound exhibits antiferromagnetic interactions.     

A 3-D Wells–Dawson phosphotungstate hybrid material modified by Na+ and a bi-copper organic complex linker,and its photo-/electro-catalytic properties

An inorganic–organic hybrid material based on Dawson polyoxometalates, [Na₂{Cu^I₂(bim)₂}₂(P₂W₁₈O₆₂)]·2H₂O (bim = biimidazole) (1), has been hydrothermally synthesized and fully characterized. In 1, each {P₂W₁₈} cluster as a hexa-node ligand connects to six adjacent Dawson clusters via six Na1 ions to generate a pure inorganic 2-D layer, further joined by bimetal–organic segments [Cu₂(bim)₂]²⁺ to form a 3-D inorganic–organic hybrid framework with channels. The structure can be simplified to 3,8-connected 3-D networks with (4³)(4¹⁸·6²⁴·8³) topology, which shows bifunctional electrocatalytic performance for oxidation of ascorbic acid (AA) and reduction of nitrite (NO₂^?), and high-efficient degradation ability for three typical dyes under UV light irradiation.     

Controlling the Reactivity of the [P8W48O184]40− Inorganic Ring and Its Assembly into POMZite Inorganic Frameworks with Silver Ions

The construction of pure‐inorganic framework materials with well‐defined design rules and building blocks is challenging. In this work, we show how a polyoxometalate cluster with an integrated pore, based on [P₈W₄₈O₁₈₄]^40? (abbreviated as {P₈W₄₈}), can be self‐assembled into inorganic frameworks using silver ions, which both enable reactions on the cluster as well as link them together. The {P₈W₄₈} was found to be highly reactive with silver ions resulting in the in situ generation of fragments, forming {P₉W₆₃O₂₃₅} and {P₁₀W₆₆O₂₅₁} in compound ( 1 ) where these two clusters co‐crystallize and are connected into a POMZite framework with 11 Ag⁺ ions as linkers located inside clusters and 10 Ag⁺ linking ions situated between clusters. Decreasing both the concentration of Ag⁺ ions, and the reaction temperature compared to the synthesis of compound ( 1 ), leads to {P₈W₅₁O₁₉₆} in compound 2 where the {P₈W₄₈} clusters are linked to form a new POMZite framework with 9 Ag⁺ ions per formula unit. Further tuning of the reaction conditions yields a cubic porous network compound ( 3 ) where {P₈W₄₈} clusters as cubic sides are joined by 4 Ag⁺ ions to give a cubic array and no Ag⁺ ions were found inside the clusters.     

Hydrothermal Combination of Trilacunary Dawson Phosphotungstates and Hexanickel Clusters: From an Isolated Cluster to a 3D Framework

Three novel hexa‐Ni‐substituted Dawson phosphortungstates [Ni₆(en)₃(H₂O)₆(μ₃‐OH)₃(H₃P₂W₁₅O₅₆)] ? 14 H₂O ( 1 ), [Ni(enMe)₂(H₂O)][Ni₆(enMe)₃(μ₃‐OH)₃(H₂O)₆(HP₂W₁₅O₅₆)] ? 10 H₂O ( 2 ), and [Ni(enMe)₂]₃[Ni(enMe)₂(H₂O)][Ni(enMe)(H₂O)₂][Ni₆(enMe)₃(μ₃‐OH)₃(Ac)₂(H₂O)(P₂W₁₅O₅₆)]₂ ? 6 H₂O ( 3 ) (en=ethylenediamine, enMe=1, 2‐diaminopropane, Ac=CH₃COO^?) have been made under hydrothermal conditions and were characterized by IR spectroscopy, elemental analysis, diffuse reflectance spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. The common structural features of compounds 1 – 3 contain the similar hexa‐Ni‐substituted Dawson polyoxometalate (POM) units that can be viewed as a [Ni₆(μ₃‐OH)₃]⁹⁺ cluster capping on a [P₂W₁₅O₅₆]^12? fragment. Compounds 1 and 2 are two isolated clusters, whereas compound 3 is the first 3D POM framework constructed from hexa‐Ni‐substituted Dawson POM units and Ni(enMe) complex bridges. The preparations of compounds 1 – 3 not only indicate that triangle coplanar Ni₆ clusters are very stable fragments in both trivacant Keggin and trivacant Dawson POM systems, but also offer that the hydrothermal technique can act as an effective strategy for making novel Dawson‐type high‐nuclear transition‐metal cluster substituted POMs by combination of lacunary Dawson precusors with transition‐metal cations in the tunable role of organic ligands. In addition, magnetic measurements illustrate that there exist overall ferromagnetic interactions in compound 3 .     

A 3D Polyoxometalate‐Based Framework Constructed from Ag/trz Metal‐Organic Ribbons and P2W18 Polyoxoanions: Synthesis,Structure and Electrochemical Properties

A Wells‐Dawson Polyoxometalate‐based hybrid, Ag₉(trz)₃(Htrz)₄ (H₂O)(P₂W₁₈O₆₂)·3H₂O ( 1 ) (Htrz = 1,2,4‐1H‐triazole) was hydrothermally synthesized through using trz ligand and silver nitrate in the presence of [P₂W₁₈O₆₂]^6– polyoxoanion. In the 3D framework structure of compound 1 , two kinds of wave‐like Ag/trz chains originated from trz ligands and silver cations are aggregated in a “2+1” mode by {Ag₂/trz} linkages to result in a 1D Ag/trz metal‐organic ribbon, which is further extended into a 3D framework structure by [P₂W₁₈O₆₂]^6– polyoxoanions through Ag‐O covalent bonds. Additionally, the electrochemical properties of compound 1 have also been investigated.     

Uranium(IV) polyoxotungstophosphates

Two tris(oxouranium)-substituted Keggin and Dawson sandwich-type tungstophosphate heteropolyanions Na₁₂[(UO)₃(H₂O)₆(PW₉O₃₄)₂]·21 H₂O (1) and Na₁₈[(UO)₃(H₂O)₆(P₂W₁₅O₅₆)₂]·27 H₂O (2) have been prepared by reaction of uranium sulphate with [PW₉O₃₄]⁹⁻ and [P₂W₁₅O₅₆]¹²⁻, respectively, in aqueous media at 4.7 pH. The products were characterized by elemental and thermal analyses, IR, UV-Vis spectroscopy and magnetical susceptibility. The results of these studies suggest that the compounds obtained from Keggin and Dawson trilacunary anions are 2∶3 sandwich-type complexes and both exhibit a square antiprismatic stereochemistry for uranium(IV) with retention of polyoxometallate parent structure.     

Cyanide Complexes Based on {Mo6I8}4+ and {W6I8}4+ Cluster Cores

Compounds based on new cyanide cluster anions [{Mo₆I₈}(CN)₆]^2–, trans-[{Mo₆I₈}(CN)₄(MeO)₂]^2– and trans-[{W₆I₈}(CN)₂(MeO)₄]²⁻ were synthesized using mechanochemical or solvothermal synthesis. The crystal and electronic structures as well as spectroscopic properties of the anions were investigated. It was found that the new compounds exhibit red luminescence upon excitation by UV light in the solid state and solutions, as other cluster complexes based on {Mo₆I₈}⁴⁺ and {W₆I₈}⁴⁺ cores do. The compounds can be recrystallized from aqueous methanol solutions; besides this, it was shown using NMR and UV-Vis spectroscopy that anions did not undergo hydrolysis in the solutions for a long time. These facts indicate that hydrolytic stabilization of {Mo₆I₈} and {W₆I₈} cluster cores can be achieved by coordination of cyanide ligands.     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face‐centered‐cubic‐type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]^18?. The cluster showed unique {Ag₇}⁵⁺‐to‐POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

FeIII48-Containing 96-Tungsto-16-Phosphate: Synthesis,Structure, Magnetism and Electrochemistry

The 48-Fe^III-containing 96-tungsto-16-phosphate, [Fe^III₄₈(OH)₇₆(H₂O)₁₆(HP₂W₁₂O₄₈)₈]³⁶⁻ ( Fe₄₈ ), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {Fe^III₆P₂W₁₂} units that are linked in an end-on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe₄₈ was synthesized by a simple one-pot reaction of an {Fe₂₂} coordination complex with the hexalacunary {P₂W₁₂} POM precursor in water. The title polyanion was characterized by single-crystal XRD, FTIR, TGA, magnetic and electrochemical studies.     

Aluminum‐ and Gallium‐Containing Open‐Dawson Polyoxometalates

Al‐ and Ga‐containing open‐Dawson polyoxometalates (POMs), K₁₀[{Al₄(μ‐OH)₆}{α,α‐Si₂W₁₈O₆₆}] · 28.5H₂O ( Al₄ ‐ open ) and K₁₀[{Ga₄(μ‐OH)₆}(α,α‐Si₂W₁₈O₆₆)] · 25H₂O ( Ga₄ ‐ open ) were synthesized by the reaction of trilacunary Keggin POM, [A‐α‐SiW₉O₃₄]^10–, with Al(NO₃)₃ · 9H₂O or Ga(NO₃)₃ · nH₂O, and unequivocally characterized by single‐crystal X‐ray analysis, ²⁹Si and ¹⁸³W NMR, and FT‐IR spectroscopy as well as elemental analysis and TG/DTA. Single‐crystal X‐ray analysis revealed that the {M₄(μ‐OH)₆}⁶⁺ (M = Al, Ga) clusters were included in an open pocket of the open‐Dawson polyanion, [α,α‐Si₂W₁₈O₆₆]^16–, which was constituted by the fusion of two trilacunary Keggin POMs via two W–O–W bonds. These two open‐Dawson structural POMs showed clear difference of the bite angles depending on the size of ionic radii. In cases of both compounds, the solution ²⁹Si and ¹⁸³W NMR spectra in D₂O showed only one signal and five signals, respectively. These spectra were consistent with the molecular structures of Al₄ ‐ and Ga₄ ‐ open , suggesting that these polyoxoanions were obtained as single species and maintained their molecular structures in solution.