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

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero-Multinuclear Metal-Oxo Clusters within Polyoxometalate Ligands

Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a "cationic metal glue strategy" for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn4 )Mn2 Ln2 (FeMn4 )} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn4 } oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the "cationic metal glue strategy" would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively.

Hexalacunary [α-H2 P2 W12 O48 ]12- Wells-Dawson Anion: X-ray Crystal Structural Evidence and Oligomerization to WO(OH2 )4+ -Bridged Dimer and Trimers

We report the first single-crystal X-ray structural evidence of the potassium salt of the hexalacunary [α-H2 P2 W12 O48 ]12- (abbreviated as {P2 W12 }) anion after its discovery by Contant and Ciabrini in 1977. In addition, we observed oligomerization of {P2 W12 } into a {WO(OH2 )}4+ -bridged Pacman-shaped [{WO(OH2 )}(α-HP2 W12 O48 )2 ]22- ({P4 W25 }) dimer and a cyclic [{WO(OH2 )}3 (P2 W12 O48 )3 ]30- ({P6 W39 }) trimer. The three phosphotungstate anions were synthesized through recrystallization of (NH4 )12 [α-H2 P2 W12 O48 ] from slightly alkaline (HOCH2 )3 CNH2 /KCl, CH3 NH3 Cl/KCl, and CH3 NH3 Cl/NH4 Cl solutions. The structure of {P2 W12 } is derived from [α-P2 W18 O62 ]6- that has six tungsten atoms one from each polar group and four from the belt-removed, and the center of the lacunary site is capped by a potassium cation. Structures of {P4 W25 } and {P6 W39 } are constructed by connecting two and three {P2 W12 } units with {WO(OH2 )}4+ , respectively. The isolation of a pure {P6 W39 } phosphotungstate framework without coordination with transition metal cations is unprecedented. Powder X-ray diffraction confirmed the bulk purity of these compounds, indicating that selective crystallization was achieved through the selection of countercations and pH.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Three rare-earth incorporating 6-peroxotantalo-4-selenates and catalytic activities for imidation reaction

Functionalization with belt lanthanide groups allows for the crystallization and structural characterization of homometallic selenotantalates, CsK[Ln(H2O)6Se4(TaO2)6(OH)3O18]·nH2O (Ln = Eu/Gd, n = 14 (STD-Eu, STD-Gd) and Ln = Lu, n = 12 (STD-Lu)). The basket-shaped {Se4(TaO2)6} archetype is assembled in a simple one-pot reaction of Na2SeO3 and K8[Ta6O19]·17H2O in acidic aqueous medium (pH 2) and in the presence of hydrogen peroxide. This unit has been proven to be an effective precursor for the preparation of a range of new POMs containing the {Se4(TaO2)6} unit. The lanthanide derivatives STD-Eu, STD-Gd and STD-Lu have been fully characterized with single-crystal X-ray diffraction, IR spectroscopy, TG analysis and PXRD in the solid state. The photoluminescence and lifetime decay behaviours of STD-Eu have been studied at room temperature, and the photoluminescence spectrum displays the characteristic emission of the Eu3+ cation. In addition, the catalytic activities of STD-Eu, STD-Gd and STD-Lu on the reaction of phthalic anhydride with phenylamines have been investigated. STD-Eu shows good catalytic activities for imidation reactions.

Robotic Stepwise Synthesis of Hetero-Multinuclear Metal Oxo Clusters as Single-Molecule Magnets

An efficient stepwise synthesis method for discovering new heteromultinuclear metal clusters using a robotic workflow is developed where numerous reaction conditions for constructing heteromultinuclear metal oxo clusters in polyoxometalates (POMs) were explored using a custom-built automated platform. As a result, new nonanuclear tetrametallic oxo clusters {FeMn₄}Lu₂A₂ in TBA₅[(A-α-SiW₉O₃₄)₂FeMn₄O₂{Lu(acac)₂}₂A₂] (II^A; A = Ag, Na, K; TBA = tetra-n-butylammonium; acac = acetylacetonate) were discovered by the installation of diamagnetic metal cations A⁺ into a paramagnetic {FeMn₄}Lu₂ unit in TBA₇[(A-α-SiW₉O₃₄)₂FeMn₄O₂{Lu(acac)₂}₂] (I). POMs II^A exhibited single-molecule magnet properties with the higher energy barriers for magnetization reversal (II^Ag, 40.0 K; II^Na, 40.3 K; II^K, 26.7 K) compared with that of the parent I (19.7 K). Importantly, these clusters with unique properties were constructed as designed by a step of the predictable sequential multistep reactions with the time-efficient platform.

Polyoxotungstate Archetype {P4 W27 } and its 3d Derivatives

The propensity of the new, phenylphosphonate-stabilized polyoxotungstate [(C6 H5 PV O)2 P4 W24 O92 ]16- to act as a precursor for new 3d metal-functionalized polyanions has been investigated. Reactions with MnII and CuII induce the formation of the previously unknown polyoxotungstate archetype {P4 W27 }, isolated as salts of the polyanions [Na⊂{MnII (H2 O)}{WO(H2 O)}P4 W26 O98 ]13- (1) and [K⊂{CuII (H2 O)}{W(OH)(H2 O)}P4 W27 O99 ]14- (2), which were characterized in the solid state (single-crystal X-ray diffraction, elemental and TG analyses, IR spectroscopy, SQUID magnetometry) and in aqueous solution (UV/Vis spectroscopy, cyclic voltammetry).

A large molecular cluster with high proton release capacity

We present a single molecular polyoxometalate cluster (K₄₁[(P₂W₁₂Nb₆O₆₂)₆{Mn₃(OH)₃(H₂O)₆}₄{Mn₃Na(H₂O)₁₆}]·26H₂O) with controllable release of a large number of protons (∼40 per molecule) in its aqueous solution upon addition of a base. The deprotonation/protonation process is reversible with the clusters remaining intact. This molecule can also absorb up to 11 protons per cluster when an acid, HCl, was added to its original aqueous solution. To the best of our knowledge, such large proton absorption/release capacity along with excellent stability is unprecedented.

Unraveling the Effects of Cobalt on Crystal Growth and Solution Behavior of Nb6P2W12-based Dimeric Clusters

We report the synthesis, characterization, and solution self-assembly of plenary Nb₆P₂W₁₂-based transition-metal substituted polyoxometalate, which is obtained by simply adding transition metals (Co²⁺) into aqueous solution containing cluster [(NbO₂)₆P₂W₁₂O₅₆]^12-, which is obtained by an in situ synthetic method. The incorporation of Co²⁺ ions significantly affects the crystal structure, resulting in the formation of a 1D chain-like crystal and the first example of a niobotungstate-based cobalt derivative cluster. The behavior and stability of this cluster in solution are confirmed by time-resolved static light scattering, dynamic light scattering, small-angle X-ray scattering, and electrospray mass spectrometry studies.

Discovery of the selenotantalate building block and its lanthanide derivatives: design, synthesis, and RhB decolorization properties

Herein we present the first Se/Ta polyoxometalate and its lanthanide derivatives with good photocatalytic activity for the decolorization of RhB.

Application of temperature-controlled chiral hybrid structures constructed from copper(ii)-monosubstituted Keggin polyoxoanions and copper(ii)-organoamine complexes in enantioselective sensing of tartaric acid

Temperature usually occupies a crucial position in the construction of chiral compounds. By controlling the temperature of the reaction system, chiral and non-chiral compounds can be designed and synthesized. Given the above, three new chiral and non-chiral compounds based on copper(ii) monosubstituted polyoxoanions and Cu(en) complexes (en = ethylenediamine), d/l-[Cu(H₂O)(en)₂]₂{[Cu(H₂O)₂(en)][SiCuW₁₁O₃₉]}·5H₂O (1, d-1 and l-1) and [Cu(H₂O)(en)₂]{[Cu(en)₂]₂[SiCuW₁₁O₃₉]}·2.5H₂O (2), were successfully synthesized under hydrothermal conditions. The main synthesis conditions of compound 1 (d-1 and l-1) and compound 2 are the same, however, the only difference is that the reaction temperatures are 80 °C and 140 °C, respectively. What's more, compounds 1 and 2 can form a 1D chiral chain by Cu–O and W/Cu–O–W/Cu bonds, respectively, and further obtain a 3D-supramolecular framework through hydrogen bonding interaction. Meanwhile, due to the asymmetry of chiral compound 1, optical second-harmonic generation (SHG) was used to investigate the second-order nonlinear optical effect and it was found that the observed SHG efficiency of compound 1 is 0.3 times that of urea. To further investigate the chiral properties, d-1 and l-1 were used in the electrochemical enantioselective sensing of d-/l-tartaric acid (d-/l-tart) molecules, respectively, which demonstrates that d-1 and l-1 have a good application prospect in sensing chiral substances.

A pair of temperature-controlled chiral compounds, d- and l-[Cu(en)₂(H₂O)]₂{[Cu(en)(H₂O)₂][SiCuW₁₁O₃₉]}·5H₂O (en = ethanediamine) are isolated by hydrothermal method, having a good application prospect in sensing d-/l-tartaric acid.

An unprecedented [{Fe5O5(OH)2(OAc)2}2{W2O2(OH)}] cluster sandwiched in the tetravacant tungstophosphate

An unprecedented [{Fe₅O₅(OH)₂(OAc)₂}₂{W₂O₂(OH)}] cluster sandwiched in two tetravacant {P₂W₁₄O₅₄} units was obtained by a one-pot reaction.

Self-assembly and Li-ion storage performance of three new Nb/W mixed-addendum polyoxometalates based on the {SiNb3W9O40} clusters and transition-metal cations

Three polyoxometalates have been synthesized to be utilized as anode materials for lithium ion batteries.

Organometallic functionalized non-classical polyoxometalates: synthesis, characterization and electrochemical properties

Two monomeric non-classical tellurium-containing heteropolymolybdate-supported metal carbonyl derivatives (NH4)5H3{[Te2Mo12(OH)O44][Mn(CO)3]}·18H2O (1) and (NH4)8{[Te2Mo12(OH)O44][Re(CO)3]}·13H2O (2) have been successfully isolated in good yields. Compounds 1 and 2 are the first two examples of metal carbonyl derivatives of heteromolybdate with tellurium as the central atom. These two compounds have been thoroughly characterized by single-crystal X-ray diffraction, elemental analyses, X-ray powder diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and UV-Vis spectroscopy. The electrochemical catalytic activities of 1 and 2 including cyclic voltammetry and catalytic oxidation of nitrite have also been investigated.

Stepwise syntheses and supramolecular assemblies of a series of polyoxovanadate hybrids with various architectures

Inorganic–organic hybrids with carbon chains of different lengths at the terminus of the organic ligands exhibit supramolecular-assemblies in different dimensions.

The homometallic polyoxotungstate archetype {P4W24}

Integration of phenylphosphonate and phenylarsonate groups render the {P₂W₁₂}-based polyoxotungstate {P₄W₂₄} accessible, yet still sufficiently reactive for consecutive functionalization steps.

Synthesis, structure, and luminescent properties of a family of lanthanide-functionalized peroxoniobiophosphates

Eight new lanthanide derivatives containing 6-peroxoniobio-4-phosphate building block, [LnIII(H2O)6]2[H4(NbO2)6P4O24]·nH2O [Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5), Er (6), Tm (7), Yb (8), 1-5, 7, 8 n = 12; 6 n = 9], have been successfully obtained using an in-situ strategy and fully characterized in the solid state by single-crystal X-ray diffraction, IR spectra, TG-MS, PXRD. Structural analyses indicate that these isostructural polyanions 1-8 consist of one [P4(NbO2)6O24]10- (P 4 (NbO 2 ) 6 ) clusters and two pendant Ln3+ cations. In these compounds, P 4 (NbO 2 ) 6 clusters are connected by lanthanide cations to form extended two-dimensional architectures. The approach takes advantage of the ability of in-situ formed P 4 (NbO 2 ) 6 cluster to build frameworks by using it as ligands to lanthanide ions. The photoluminescence (PL) and lifetime decay behaviors of 1, 3 and 4 in solid state have been performed at room temperature. The PL emission of 1, 3 and 4 is mainly derived from the characteristic 5D0→7FJ (J = 1, 2, 3, 4), 5D4→7FJ (J = 6, 5, 4, 3) and 4F9/2→6H J (J = 15/2, 13/2, 11/2) transitions of the EuIII, TbIII and DyIII cations, respectively.

Details make the difference: a family of tetranuclear CuIIMnIII complexes with cube-like and double open cube-like cores

The "direct synthesis" approach, namely one-pot reaction of metal powders and ammonium salt with a methanol solution of a polydentate Schiff base (H₂L) formed in situ from salicylaldehyde and ethanolamine, has been successfully used for the preparation of the new heterometallic compounds [Cu₃Mn(L)₄(CH₃OH)₃]I₃ (1), [Cu₃Mn(L)₄(CH₃OH)₃(H₂O)]NCS·H₂O (2), [Cu₃Mn(L)₄(CH₃OH)(H₂O)_2.55]Br·0.45H₂O (3) and [Cu₃Mn(L)₄(H₂O)_3.4]BF₄·0.6H₂O (4). Crystallographic analysis revealed that 1-4 are based on the tetranuclear core {CuMn^III(μ₃-O)₄} where the metal centres are joined by the oxygen bridges of Schiff base ligands forming a cube-like arrangement. The novel heterometallic compound [Cu₃Mn(L)₄(CH₃OH)₃]₂[Mn(NCS)₄]·2CH₃OH (5) has been obtained by the "building block" approach using the reaction of [Cu(HL)₂] with manganese acetate and NH₄NCS in methanol. The crystal structure of 5 revealed the {CuMn^III(μ-O)₂(μ₃-O)₂} metal core which can be viewed as a double open cube. In spite of a similar {Cu₃MnO₄} atom set in the cores of 1-5, the complexes show rather different molecular structures and significantly differ by the number and combinations of coordinated CH₃OH/H₂O solvent molecules. Variable-temperature (2-300 K) magnetic susceptibility along with variable-field magnetization measurements of 1-5 showed a decrease of the effective magnetic moment value at low temperature, indicative of the antiferromagnetic coupling of medium size (-55 to -22 cm^-1). For these systems resembling a compressed prism the coupling constant in walls J₄ correlates with the averaged bonding angles in walls α: J₄vs. α develops approximately according to a straight line.

Discovery of Heteropolytantalate: Synthesis and Structure of Two 6-Peroxotantalo-4-phosphate Clusters

Polyoxometalates (POMs) of Nb and Ta are greatly different from those of Mo, W, and V that have been studied extensively and developed well. The latter can be formed simply by acidification of their aqueous monomeric oxoanions and has found application areas from catalysis to magnetism, materials science, medicine, and nanotechnology. Even now the polyoxoniobate (PONb) chemistry has accelerated dramatically over the last 15 years, and a vast expansion of available PONbs has been reported. However, after nearly 200 years of POM research, Ta-based POM chemistry is still at its infant stage and only dominated by the isopolyoxotantalate ions (Ta₆ and Ta₁₀) and transition-metal-capped Ta₆ species, along with two Ti-substituted polyoxotantalates [Ti₂Ta₈O₂₈]^8- and [Ti₁₂Ta₆O₄₄]^10- reported very recently. In this study, we discover two novel peroxotantalophosphate clusters [P₄(TaO₂)₆O₂₅]^12- (1) and [P₄(TaO₂)₆O₂₄]^10- (2) by incorporating phosphorus heteroatom into Ta-oxo framework, which represent the first two examples of heteropolytantalate. Interestingly, two P₂Ta₃ half-units are cis- and trans-condensed in 1 and 2, leading to "open" and "closed" configurations, respectively. These two chemically and structurally related clusters can be isolated in a controlled manner, and the yields are relatively high. Both compounds were characterized in the solid state by single-crystal X-ray diffraction, ³¹P MAS NMR, FT-IR, TGA, and elemental analysis as well as by ³¹P NMR in solution. The results presented here provide a strategy to be applicable to other heteroatom-incorporated polyoxotantalates and further expand the phase space for polyoxotantalate chemistry.

A luminescent polyoxoniobate lanthanide derivative {Eu3(H2O)9[Nb48O138(H2O)6]}27−

An Eu-containing polyoxoniobate (CN₃H₆)₇K₃H₁₇{Eu₃(H₂O)₉Nb₄₈O₁₃₈(H₂O)₆}·40H₂O is obtained under the protection of citric acid, which is a triangular cylindrical entity and displays red emission.

Two nanoscale Nb containing polyoxometalates based on {P2W15Nb3O62} clusters and chromium cations

We have introduced mixed-addenda Nb/W polyoxometalates as a new class of materials for lithium-ion batteries and demonstrated their capability as anode materials with good cycling stability.

A Ni-containing decaniobate incorporating organic ligands: synthesis, structure, and catalysis for allylic alcohol epoxidation

Na₈{Ni[Ni(en)]₂Nb₁₀O₃₂}·28H₂O, representing the first example of trinuclear nickel-containing polyoxoniobate, has been synthesized. It was found to catalyze the epoxidation of 3-methyl-2-buten-1-ol with high conversion and selectivity.

Synthesis, structure, and photocatalytic hydrogen evolution of a trimeric Nb/W addendum cluster

We present the second trimeric Nb/W addendum cluster Cs₁₂[(SiW₉Nb₃O₃₈)₃WO₃(OH)₃]·33H₂O with its photocatalytic hydrogen evolution activity.

Manganese clusters of aromatic oximes: synthesis, structure and magnetic properties

With the aim of tuning the structures by using oxime ligands with different non-coordinating groups, three aromatic oxime ligands were designed by fusing oxime groups ([double bond, length as m-dash]N-OH) onto different non-coordinating groups. Their reactions with the corresponding Mn(ii) salts gave five manganese clusters [Mn(μ₃-O)(L¹)₃(DMF)(H₂O)₃Cl]·2DMF·CH₃OH (1), [Mn(μ₃-O)(L²)₃(OAc)(CH₃OH)₂] (2), [Mn(μ₃-O)₂(L²)₆(H₂O)(py)₇](ClO₄)₂·py·0.5CH₃OH·2H₂O (3), [MnO₄(L²)₈(DMF)₄]·DMF·6CH₃CN (4), and [MnMnO₄(L³)₁₂]·3DMF·6H₂O (5), in which H₂L¹, H₂L² and HL³ represent indane-1,2,3-trione-1,2-dioxime, acenaphthenequinone dioxime, and 9,10-phenanthrenedione-9-oxime, respectively. Their structures were determined and studied in detail. 1 and 2 show planar triangular trinuclear Mn structures. 3 has a hexanuclear Mn skeleton formed from two Mn triangular units through inter-trinuclear mutual coordination. 4 and 5 present octanuclear skeletons constructed from planar triangular Mn₃O and tetrahedral Mn₄O secondary building units, respectively, with different symmetries and different oxidation states of the manganese ions. Their structural studies reveal a significant contribution of the parent rings for fusing oxime groups, different non-coordinating groups and anions to the formation of different cluster skeletons. Their magnetic properties were investigated and simulated, which revealed the presence of dominant antiferromagnetic interactions between the metal ions in these compounds.

Insight into the reactivity of in situ formed {(NbO2)3SiW9}: synthesis, structure, and solution properties of a trimeric polytungstosilicate trapping a {MnNb9} core

The first example of the trimeric polyoxometalate cluster, Cs₁₀Na₃[(SiW₉Nb₃O₃₈)₃MnO₃(H₂O)₃]·18H₂O (1a), has been synthesized using an in situ synthetic strategy and thoroughly characterized.