A water-soluble mixed-valent {Mn11} cluster embedded heteropolyoxoniobate with magnetic properties

A rare all-inorganic high-nuclearity mixed-valent {Mn11} cluster embedded polyoxoniobate, K25H43{(Te4Nb9O33)3(Nb6O19)5(TeVINb5O14)[(TeIVO3)2(MnII7MnIII4O19)]}·97H2O (1), has been synthesized by a one-pot reaction. Compound 1 contains the largest manganese cluster {Mn11} core among polyoxoniobates reported to date. {Mn11} consists of three quasi-cubane {Mn3O4} units and is simultaneously encapsulated by lacunary α-Keggin {Te4Nb9O36} and Lindqvist {Nb6O19} units. Compound 1 exhibits significant magnetic anisotropy and excellent water solubility and stability. The findings suggest a new, all-inorganic polynulear Mn-based structural paradigm for aqueous solution chemistry and magnetic materials.

An organophosphate 3d-4f heterometallic polyoxoniobate nanowire

Four different structural compositions of organophosphate, 3d transition metal, 4f lanthanide and polyoxoniobate (PONb) are unified in a system for the first time to form a new type of organophosphate 3d-4f heterometallic inorganic-organic hybrid PONb nanowire. Interesting magnetic anisotropy and slow magnetic relaxation are found in the PONb nanowire.

{Mo4}-directed structural evolution of highly reduced molybdenum red clusters for efficient proton conduction

A series of highly reduced Mo red clusters {Mo28} (1), {Mo30} (2), and {Mo40} (3) are synthesized from the rational assembly of planar {MoV4} building blocks and employed for proton conduction. 3 exhibits the best conductivity of 7.56 × 10-3 S cm-1 under optimal conditions due to the most efficient hydrogen-bonding network.

A Giant Heterometallic Polyoxometalate Nanocluster for Enhanced Brain-Targeted Glioma Therapy

Giant heterometallic polyoxometalate (POM) clusters with precise atom structures, flexibly adjustable and abundant active sites are promising for constructing functional nanodrugs. However, current POM drugs are almost vacant in orthotopic brain tumor therapy due to the inability to effectively penetrate the blood-brain barrier (BBB) and low drug activity. Here, we designed the largest (3.0 nm × 6.0 nm) transition-metal-lanthanide co-encapsulated POM cluster {[Ce10 Ag6 (DMEA)(H2 O)27 W22 O70 ][B-α-TeW9 O33 ]9 }2 88- featuring 238 metal centers via synergistic coordination between two geometry-unrestricted Ce3+ and Ag+ linkers with tungsten-oxo cluster fragments. This POM was combined with brain-targeted peptide to prepare a brain-targeted nanodrug that could efficiently traverse BBB and target glioma cells. The Ag+ active centers in the nanodrug specifically activate reactive oxygen species to regulate the apoptosis pathway of glioma cells with a low half-maximal inhibitory concentration (5.66 μM). As the first brain-targeted POM drug, it efficiently prolongs the survival of orthotopic glioma-bearing mice.

Structure and Electronic Properties of Large Oligomeric Heterometallic 3d/CeIV Polyoxometalates

Merging the rich chemistry of Ce(IV) polyoxometalates (POMs) with that of 3d polyanions remains a challenge due to the strong competition between these highly oxophilic lanthanide cations and 3d metallic ions for coordination to lacunary molecular metal oxides. We report herein the characterization of an unprecedented water stable hexameric CeIV/CoII POM (Ce12Co6) made of two {(SiW9)2Ce6} units connected to a {(SiW10)2Co6(PO4)2} core. In addition, the pentameric CeIV/NiII compound Ce6Ni8, where two {PW9Ni3W} and a {PW10Ni2} fragments are grafted on a {(PW9)2Ce6} moiety, has been obtained. Magnetic studies of Ce6Ni8 revealed ferromagnetic interactions between the NiII centers constituting the {Ni3PW10} fragments, in agreement with the geometry of such a trinuclear cluster. Related insoluble barium salts of Ce12Co6 and Ce6Ni8 were also prepared, allowing their solid-state electrochemical investigations and showing in particular that in Ce12Co6, both the cobalt, cerium, and silicotungstate moieties are electroactive. Finally, photophysical studies demonstrate the formation of long-lived reduced POMs photosensitized by [Ru(bpy)3]2+, suggesting that Ce12Co6 and Ce6Ni8 could be used as efficient reservoirs of reduction equivalents for photocatalytic reactions.

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.

[α-AsW9O33]9- bridged hexagonal clusters of Ln(III) showing field induced SMM behavior: experimental and theoretical insight

Polyoxometalates (POM), as inorganic polydentate oxygen donors, provide binding opportunities for oxophilic lanthanide metal centers to construct novel Ln-substituted POM materials with exciting structures and attractive properties. Herein, we have reported four arsenotungstate [α-AsW₉O₃₃]^9- based lanthanide-containing polyoxometalates [Cs_xK_36-x{Ln₆(H₂O)₁₂(α-AsW₉O₃₃)₆}]·yH₂O (Ln = Er (1), Gd (2), Ho (3), and Tb (4)), which are synthesized in an alkaline medium. Complexes 1-3 are the dimeric structures of [Ln₃(H₂O)₆(α-AsW₉O₃₃)₃]^18- polyanions, whereas complex 4 is a hexamer of the polyanion [Tb (H₂O)₂(α-AsW₉O₃₃)]^6- as a building unit. In all the complexes, [α-AsW₉O₃₃]^9- units are staggered up and down and give rise to the chair conformation, where one [α-AsW₉O₃₃]^9- unit bridges two Ln(III) centers through four μ₂-oxygen and two terminal oxygen atoms, resulting in the hexagonal arrangement of lanthanides. The dynamic magnetic measurement indicates that only complex 1 exhibits slow relaxation of magnetization with an applied dc field (1500 Oe). To gain insight into the slow relaxation of magnetization in complex 1, the ligand-field parameters and the splitting of the ground-state multiplet of the Er(III) ions have been estimated. The ab initio calculation results confirm that the ground state wave function of these molecules (1, 3, and 4) is mainly composed of a mixture of m_J states, and the non-axial crystal field (CF) terms are more predominant than the axial CF term. The solid-state fluorescence spectra of 1-4 reveal that the photoexcitation O → M ligand-to-metal charge-transfer (LMCT) of arsenotungstate fragments is effectively quenched due to the spatial coordination environment around the Ln(III) ion.

Recent Progress for Single-Molecule Magnets Based on Rare Earth Elements

Single-molecule magnets (SMMs) have attracted much attention due to their potential applications in molecular spintronic devices. Rare earth SMMs are considered to be the most promising for application owing to their large magnetic moment and strong magnetic anisotropy. In this review, the recent progress in rare earth SMMs represented by mononuclear and dinuclear complexes is highlighted, especially for the modulation of magnetic anisotropy, effective energy barrier (U_eff) and blocking temperature (T_B). The terbium- and dysprosium-based SMMs have a U_eff of 1541 cm^-1 and an increased T_B of 80 K. They break the boiling point temperature of liquid nitrogen. The development of the preparation technology of rare earth element SMMs is also summarized in an overview. This review has important implications and insights for the design and research of Ln-SMMs.

Heteroatom-Modulated Assembly of Hexalanthanoid-Containing Polyoxometalate-Based Coordination Networks

Two series of lanthanoid (Ln)-containing polyoxometalates (POMs) {[Ln₆(ampH)₄(H₂O)_24-n(ampH₂)_n(PW₁₁O₃₉)₂]·21H₂O (Ln = Tb, n = 0 (1), Ln = Er, n = 1 (2)) and K₂[Ln₆(ampH)₄(H₂O)₂₂(SiW₁₁O₃₉)₂]·23H₂O (Ln = Tb (3), Er (4)) (ampH₂ = (aminomethyl) phosphonic acid)} have been synthesized with tri-lacunary Keggin-type POMs containing different types of heteroatoms. Compounds 1 and 2 display neutral organic-inorganic hybrid POM molecules containing {Ln₆(ampH)₄} ({Ln₆}) cores sandwiched by two {PW₁₁O₃₉} units. By changing the heteroatoms from P^V to Si^IV, the extended 2D networks of 3 and 4 were successfully isolated where the adjacent {Ln₆} clusters were connected by {SiW₁₁O₃₉} moieties. Luminescence performances and magnetic properties of 1-4 have been systematically surveyed. The solid-state fluorescence spectra of 1-4 display characteristic emissions of Ln components resulting from the 4f-4f transitions, and energy transfer from the POM segments to Ln³⁺ centers in 1 and 3 has been observed based on the lifetime decay behaviors. Furthermore, all compounds can be utilized as electrocatalysts toward reduction of nitrite with high stability.

Polyoxometalate-Viologen Thermochromic Hybrids for Organic Amine Detectors and Memristors with Temperature-Regulating Resistance Switching Characteristics

There are relatively few reports on the combination of viologen and polyoxometalates (POMs). Herein, we successfully synthesized three viologen-POM-based compounds by in situ transformation of ligands under hydrothermal conditions, namely, {M^II(1,4-cby)₂[H₂(γ-Mo₈O₂₆)]}·nH₂O (1: M = Ni, n = 4; 2: M = Co, n = 6), and [Ni^II(1,3-cby)(H₂O)₄(β-Mo₈O₂₆)_0.5]·2H₂O (3) (1,4-cby·Cl = 1-(4-carboxy-benzyl)-[4,4']bipyridinyl-1-ium, 1,3-cby·Cl = 1-(3-carboxy-benzyl)-[4,4']bipyridinyl-1-ium). Isostructural compounds 1 and 2 exhibit two-dimensional (2D) layer structures with POMs as linking nodes, while compound 3 shows a one-dimensional (1D) metal-organic chain with dissociative POM anions. When the temperature increases, compounds 1-3 show good reversible thermochromism properties and also have a fluorescence quenching effect. Moreover, compounds 1-3 can also be used as detectors for organic amines, especially in the atmosphere of ammonia, ethylenediamine, and diethylamine with an obvious discoloration effect. In addition, compound 1 was used as a material for the preparation of memristors with superior properties (distinct temperature-adjusted resistive switching properties). It shows bipolar resistive switching (RS) behavior at different temperatures of 20, 50, and 100 °C. The results show that the 1-based memristor has good thermal stability, which is important for high-temperature environment applications. It also shows that crystalline viologen-POM-based compounds are ideal candidates for making memristors.

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.

Assemblies of Increasingly Large Ln-Containing Polyoxoniobates and Intermolecular Aggregation-Disaggregation Interconversions

An oxalate-assisted lanthanide (Ln) incorporation strategy is first demonstrated for creating rare high-nuclearity Ln-containing polyoxoniobates (PONbs). With the strategy, a series of high-nuclearity Ln-containing PONbs of 50-nuclearity Dy₂Nb₄₈, 103-nuclearity Dy₇Nb₉₆, 200-nuclearity Dy₁₀Nb₁₉₀, and 206-nuclearity Dy₁₄Nb₁₉₂ have been made, showing an increasingly large structure evolution from Dy₂Nb₄₈ monomer to Dy₇Nb₉₆ dimer and to distinct Dy₁₀Nb₁₉₀ and Dy₁₄Nb₁₉₂ tetramers. Among them, Dy₁₄Nb₁₉₂ presents the largest heterometallic PONb and also the PONb with the greatest number of Ln ions reported thus far. Interestingly, both giant Dy₁₄Nb₁₉₂ and Dy₁₀Nb₁₉₀ molecules can further undergo single-crystal to single-crystal intermolecular aggregations, forming infinite {Dy₁₄Nb₁₉₂}_∞ and {Dy₁₀Nb₁₉₀}_∞ chains, respectively. The former structural transformation shows a reversible humidity-dependent aggregation-disaggregation process accompanied by a proton conductivity response, while the latter structural transformation is irreversible. These new species largely enrich the very limited members of Ln-containing PONb family and offer rare examples for studying structural transformations between giant molecular aggregates and infinitely extended structures at the atomic level.

NMR Relaxivities of Paramagnetic, Ultra-High Spin Heterometallic Clusters within Polyoxometalate Matrix as a Function of Solvent and Metal Ion

Selectivity and image contrast are always challenging in magnetic resonance imaging (MRI), which are - inter alia - addressed by contrast agents. These compounds still need to be improved, and their relaxation properties, i. e., their paramagnetic relaxation enhancement (PRE), needs to be understood. The main goal is to improve specificity and relaxivities, especially at the high magnetic fields currently exploited not only in material science but also in the medical environment. Longitudinal and transverse relaxivities, r₁ and r₂ , which correspond to the longitudinal and transverse relaxation rates R₁ and R_2, normalized to the concentration of the paramagnetic moieties, need to be considered because both contribute to the image contrast. ¹ H-relaxivities r₁ and r₂ of high-spin heterometallic clusters were studied containing lanthanide and transition-metal ions within a polyoxometalate matrix. A wide range of magnetic fields from 0.5 T/20 MHz to 33 T/1.4 GHz was applied. The questions addressed here concern the rotational and diffusion correlation times which determine the relaxivities and are affected by the solvent's viscosity. Moreover, the variation of the lanthanide and transition-metal ions of the clusters provided insights into the sensitivity of PRE with respect to the electron spin properties of the paramagnetic centers as well as cooperative effects between lanthanides and transition metal ions.

Two Innovative Fumaric Acid Bridging Lanthanide-Encapsulated Hexameric Selenotungstates Containing Mixed Building Units and Electrochemical Performance for Detecting Mycotoxin

Two particular fumaric acid bridging lanthanide-encapsulated selenotungstates [H₂N(CH₃)₂]₁₆Na₈[Ln₃(H₂O)₇]₂ [W₄O₈(C₄H₂O₄) (C₄H₃O₄)]₂[SeW₆O₂₅]₂[B-α-SeW₉O₃₃]₄·46H₂O [Ln = Ce³⁺ (1), La³⁺ (2)] were acquired by the deliberately designed step-by-step synthetic strategy, which are composed of four trilacunary Keggin [B-α-SeW₉O₃₃]^8- and two original [SeW₆O₂₅]^10- building units together with one fumaric acid bridging heterometallic [Ln₃(H₂O)₇]₂[W₄O₈(C₄H₂O₄) (C₄H₃O₄)]₂²⁸⁺ entity. Particularly, this heterometallic cluster contains four fumaric acid ligands, which play two different roles: one works as the pendant decorating the cluster and the other acts as the linker connecting the whole structure. In addition, the 1@DDA hybrid material was produced through the cation exchange of 1 and dimethyl distearylammonium chloride (DDA·Cl) and its beehive-shaped film of 1@DDA was prepared by the breath figure method, which can be further used to establish an electrochemical biosensor for detecting a kind of mycotoxin-ochratoxin A (OX-A). The 1@DDA beehive-shaped film-based electrochemical biosensor exhibits good reproducibility and specific sensing toward OX-A with a low detection limit of 29.26 pM. These results highlight the huge feasibility of long-chain flexible ligands in building lanthanide-encapsulated selenotungstates with structural complexity and further demonstrate great electrochemical application potentiality of polyoxometalate-involved materials in bioanalysis, tumor diagnosis, and iatrology.

A Three-Dimensional (3D) Indium-Containing Polyoxoniobate Framework Based on {In5Nb71}n Helical Pillars

A rare 3D Indium-containing polyoxoniobate framework {H₉[Cu(en)₂(H₂O)₂][Cu(en)₂]₁₂[In(en)]₅[Nb₂₃-O₆₅(OH)₃(H₂O)₂]{Nb₂₄O₆₇(OH)₂(H₂O)₃]₂}·68H₂O(1), based on the In-containing polyoxoniobate cluster, {[In(en)]₅[Nb₂₃O₆₅(OH)₃(H₂O)₂][Nb₂₄O₆₇(OH)₂(H₂O)₃]₂}^35- ({In₅Nb₇₁}) and [Cu(en)₂]²⁺ linkers has been successfully synthesized. The nest-like cluster {In₅Nb₇₁} is constructed from one brand-new V-shaped {Nb₂₃O₇₀}, two triangle-shaped {Nb₂₄O₇₂} and five [In(en)]³⁺. The [In(en)] fragments link {Nb₂₄O₇₂} and {Nb₂₃O₇₀} units into unique {In₅Nb₇₁}_n helical pillars. The copper-amine complexes connect the {In₅Nb₇₁}_n helical pillars into a three-dimensional (3D) inorganic-organic hybrid In-Cu-containing framework. This material also exhibits good ionic conductivity and vapor adsorption capacity properties.

The largest Se-4f cluster incorporated polyoxometalate with high Lewis acid-base catalytic activity

A 4p-4f cluster incorporated polyoxometalate (POM), namely, H₁₈{[(H₄pic)₄Eu₁₀Se₁₃O₂₈(H₂O)₁₂](α-GeW₉O₃₄)₄·40H₂O (1-Eu, H₄pic = isonicotinic acid), has been first synthesized and characterized. 1-Eu features an interesting four-shell structure, representing the largest Se-4f cluster incorporated POM known to date. Besides, 1-Eu exhibits excellent Lewis acid-base catalytic activity and reusablity in catalyzing the gram-scale dehydration condensation reaction of hydrazines and 1,3-diketones to synthesize polysubstituted pyrazoles.

NMR Relaxivities of Paramagnetic Lanthanide-Containing Polyoxometalates

The current trend for ultra-high-field magnetic resonance imaging (MRI) technologies opens up new routes in clinical diagnostic imaging as well as in material imaging applications. MRI selectivity is further improved by using contrast agents (CAs), which enhance the image contrast and improve specificity by the paramagnetic relaxation enhancement (PRE) mechanism. Generally, the efficacy of a CA at a given magnetic field is measured by its longitudinal and transverse relaxivities r1 and r2, i.e., the longitudinal and transverse relaxation rates T1-1 and T2-1 normalized to CA concentration. However, even though basic NMR sensitivity and resolution become better in stronger fields, r1 of classic CA generally decreases, which often causes a reduction of the image contrast. In this regard, there is a growing interest in the development of new contrast agents that would be suitable to work at higher magnetic fields. One of the strategies to increase imaging contrast at high magnetic field is to inspect other paramagnetic ions than the commonly used Gd(III)-based CAs. For lanthanides, the magnetic moment can be higher than that of the isotropic Gd(III) ion. In addition, the symmetry of electronic ground state influences the PRE properties of a compound apart from diverse correlation times. In this work, PRE of water 1H has been investigated over a wide range of magnetic fields for aqueous solutions of the lanthanide containing polyoxometalates [DyIII(H2O)4GeW11O39]5- (Dy-W11), [ErIII(H2O)3GeW11O39]5- (Er-W11) and [{ErIII(H2O)(CH3COO)(P2W17O61)}2]16- (Er2-W34) over a wide range of frequencies from 20 MHz to 1.4 GHz. Their relaxivities r1 and r2 increase with increasing applied fields. These results indicate that the three chosen POM systems are potential candidates for contrast agents, especially at high magnetic fields.

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.

NiII 36 -Containing 54-Tungsto-6-Silicate: Synthesis, Structure, Magnetic and Electrochemical Studies

The 36-NiII -containing 54-tungsto-6-silicate, [Ni36 (OH)18 (H2 O)36 (SiW9 O34 )6 ]6- (Ni36 ) was synthesized by a simple one-pot reaction of the Ni2 -pivalate complex [Ni2 (μ-OH2 )(O2 CCMe3 )4 (HO2 CCMe3 )4 ] with the trilacunary [SiW9 O34 ]10- polyanion precursor in water and structurally characterized by a multitude of physicochemical techniques including single-crystal XRD, FTIR, TGA, elemental analysis, magnetic and electrochemical studies. Polyanion Ni36 comprises six equivalent {NiII 6 SiW9 } units which are linked by Ni-O-W bridges forming a macrocyclic assembly. Magnetic studies demonstrate that the {Ni6 } building blocks in Ni36 remain magnetically intact while forming a hexagonal ring with antiferromagnetic exchange interactions between adjacent {Ni6 } units. Electrochemical studies indicate that the first reduction is reversible and associated with the WVI/V couple, whereas the second reduction is irreversible attributed to the NiII/0 couple.

Assembly of tetra-nuclear YbIII-containing selenotungstate clusters: synthesis, structures, and magnetic properties

Two tetra-nuclear Yb^III-incorporated selenotungstate clusters, Keggin (C₂H₈N)₆Na₁₄[Yb₄Se₆W₄₄O₁₆₀(H₂O)₁₂]·40H₂O (1) and Wells-Dawson (C₂H₈N)₄Na₁₄[Yb₄Se₆W₄₅O₁₅₉(OH)₆(H₂O)₁₁]·38H₂O (2), have been isolated through a pH-controlled assembly, which exhibit the first Yb^III-containing polyoxotungstates with selenium heteroatoms. Their assemblies rely on the structure-directing effects of SeO₃^2- anion templates to give rise to available Se-containing Keggin-/Wells-Dawson-type motifs. Both compounds were characterized by single-crystal X-ray diffraction, IR spectroscopy, power X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) as well as electrospray ionization mass spectrometry (ESI-MS). Furthermore, systematic magnetic studies revealed that 1 exhibits field-induced single-molecule magnetic behavior with a pre-exponential factor of τ₀ = 6.60(7) × 10^-8 s and a relaxation energy barrier of ΔE/k_B = 39.44(2) K, while 2 only displays antiferromagnetic interactions between the ytterbium centers.

Organoamine-Directed Assembly of 5p-4f Heterometallic Cluster Substituted Polyoxometalates: Luminescence and Proton Conduction Properties

The assembly of heterometallic cluster substituted polyoxometalates (POMs) remains a great challenge for inorganic synthetic chemistry up to now. Herein, a series of 5p-4f heterometallic cluster substituted POMs were successfully isolated by a facile one-step hydrothermal reaction method, namely H₁₇(H₂en)₃[Sb^III₉Sb^VLn₃O₁₄(H₂O)₃][(SbW₉O₃₃)₃(PW₉O₃₄)]·28H₂O(1-Ln, Ln = Ce, Sm, Eu, Gd, Tb, Dy) (en = ethylenediamine). Interestingly, by replacing en with imidazole, another series of 5p-4f heterometallic cluster substituted POMs H₁₃(HIm)₄K₂Na₄(H₂O)₉[Sb^III₉Sb^VLn₃O₁₄(H₂O)₃][(SbW₉O₃₃)₃(PW₉O₃₄)]·26H₂O (2-Ln, Ln = Sm, Eu, Gd, Tb, Dy, Im = imidazole) were obtained. Structural analyses indicate that both 1-Ln and 2-Ln are made up of an unprecedented 5p-4f heterometallic {Sb₁₀Ln₃O₁₄(H₂O)₃} cluster stabilized simultaneously by mixed trilacunary heteropolyanions including {A-α-PW₉O₃₄} and {B-α-SbW₉O₃₃}. Impedance measurements indicate that both compounds exhibit different proton conduction properties, and the conductivity of 2 can reach up to 1.64 × 10^-2 S cm^-1 at 85 °C under 98% relative humidity. Moreover, the fluorescence emission behaviors of both compounds have been studied.

3d-4f Heterometallic cluster incorporated polyoxoniobates with magnetic properties

A series of 3d-4f heterometallic cluster incorporated polyoxoniobates (PONbs) with different magnetic properties were first made and characterized. This work not only provides a promising strategy to make new heterometallic cluster incorporated PONbs but also demonstrates an ideal model to probe how transition-metal ions influence the magnetic property of PONbs.

Trigonal Prismatic Coordination of Discrete Rare Earth Ions, Enforced by the Polyoxotungstate [P4 W27 O99 (H2 O)]16

A family of solution‐stable polyanions [Na⊂{Ln^III(H₂O)}{W^VIO(H₂O)}P^V₄W^VI₂₆O₉₈]¹²⁻ (Ln=Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) represent the first examples of polyoxometalates comprising a single lanthanide(III) or yttrium(III) ion in a rare trigonal prismatic O₆ environment. Their synthesis exploits the reactivity of the organophosphonate‐functionalized precursor [P₄W₂₄O₉₂(C₆H₅P^VO)₂]¹⁶⁻ with heterometal ions and yields hydrated potassium or mixed lithium/potassium salts of composition K_xLn_yH_12–x–y[Na⊂{Ln(H₂O)}{WO(H₂O)}P₄W₂₆O₉₈]⋅nH₂O⋅mLiCl (x=8.5–11; y=0–2; n=24–34; m=0–1.5). The Dy, Ho, Er and Yb derivatives are characterized by slow magnetization relaxation.

Deliberate Construction of Polyoxoniobates Exploiting the Carbonate Ligand

Polyoxometalates (POMs, metals=V^V , Nb^V , Ta^V , Mo^VI , W^VI ) are molecular metal oxides that can be isolated without capping ligands. The high negative charge of polyoxoniobates (PONb) provides strong interactions with heterocations, advantageous for electrostatic assembly of modular materials. In four single-crystal X-ray structures, we demonstrate that carbonate combined with the very reactive decaniobate [Nb₁₀ O₂₈ ]^6- reassembles into a new decaniobate, [Nb₁₀ O₂₅ (CO₃ )₆ ]^12- , featuring three carbonate-ligated Nb-polyhedra. These Nb-sites can be replaced by heterometals (lanthanides), and the tridentate carbonate can serve as an anchor point to build niobate-frameworks. Small-angle X-ray scattering and two additional X-ray structures reveal that the reaction pathway proceeds through a Nb₂₄ -PONb intermediate, and the obtained PONb (with or without carbonate) is counterion, temperature, and solvent-dependent (water or mixed water-methanol). This provides an uncommon level of control for PONb chemistry.

Sandwich-Type Uranyl Phosphate-Polyoxometalate Cluster Exhibiting Strong Luminescence

A pure inorganic uranyl phosphate-polyoxometalate of Na₁₇{Na@[(SbW₉O₃₃)₂(UO₂)₆(PO₃OH)₆]}·xH₂O (abbreviated as Na@U₆P₆, with x ≈ 46) featuring a sandwich-type structure was prepared using Keggin-type trilacunary [α-B-SbW₉O₃₃]^9- units as building blocks, which were formed in situ by SbCl₃ and Na₂WO₄·2H₂O. Crystal structural analysis showed that six UO₂²⁺ cations and six PO₃OH^2- anions generated a wheel-like cluster unit with a Na⁺ center ([Na@(UO₂)₆(PO₃OH)₆]⁺) that is stabilized by two [α-B-SbW₉O₃₃]^9- units. Na@U₆P₆ displayed a solid-state photoluminescence quantum yield of 33% at 300 K. The temperature-dependent fluorescence emission spectra showed that Na@U₆P₆ has temperature-sensitive fluorescence in which its emission intensity decreased by 77% as the temperature increased from 200 to 300 K. These results suggest that such uranyl phosphate-polyoxometalate clusters could serve as potential temperature-sensitive molecular materials.

A trapped hexaaqua CoII complex between the polyanionic sheets of decavanadate reveals high axial anisotropy and field induced SIM behaviour

In this work, we report an inorganic compound [{Co(H₂O)₆}²⁺{Na₄V₁₀O₂₈}^2-] (1) in which the polyanionic sheets of decavanadate play the role of a diamagnetic matrix that reduces the dipolar-dipolar and spin-spin interactions between [Co(H₂O)₆]⁺² units to suppress the fast tunnelling of magnetization. Structural analysis reveals that each [Co(H₂O)₆]⁺² complex is surrounded by four decavanadates and separated by a large internuclear distance (9 Å). It was also found that the adjacent decavanadates are connected via sodium ions and form a 2D sheet of the inorganic layer in which the [Co(H₂O)₆]²⁺ ions are present in between two layers. Detailed dc (direct current) and ac (alternating current) magnetic measurements disclose the presence of large easy-axis anisotropy (D = -102 cm^-1) and field induced slow magnetic relaxation behaviour with a spin reversal barrier of U_eff = 50 K. Additionally, the temperature dependence of the relaxation time reveals that the Raman and QTM processes mainly play an important role rather than the thermally activated Orbach process in the overall relaxation dynamics of the studied compound. To analyse the electronic structure and magnetic properties of compound 1, ab initio calculations were performed which further support the experimental observations. Notably, the U_eff value of 1 represents the highest energy barrier reported for POM based SMMs with transition metal ions to date.

A Giant 3d-4f Polyoxometalate Super-Tetrahedron with High Proton Conductivity

The assembly of gigantic heterometallic metal clusters remains a great challenge for synthetic chemistry. Herein, based on the slow release strategy of lanthanide ions and in situ formation of lacunary polyoxometalates, two giant 3d-4f polyoxometalate inorganic clusters [LaNi₁₂ W₃₅ Sb₃ P₃ O₁₃₉ (OH)₆ ]^23- (LaNi₁₂ ) and [La₁₀ Ni₄₈ W₁₄₀ Sb₁₆ P₁₂ O₅₆₈ (OH)₂₄ (H₂ O)₂₀ ]^86- (La₁₀ Ni₄₈ ) are obtained. The nanoscopic inorganic cluster La₁₀ Ni₄₈ possesses a super tetrahedron structure, which can be viewed as assembly from four LaNi₁₂ molecules encapsulating a central [La₆ (SbO₃ )₄ (H₂ O)₂₀ ]⁶⁺ octahedron core. This giant aesthetic La₁₀ Ni₄₈ tetrahedron containing 214 metal ions is the largest 3d-4f cluster reported thus far in polyoxometalate system. More interestingly, the LaNi₁₂ and La₁₀ Ni₄₈ display high stability in solution and La₁₀ Ni₄₈ displays excellent proton conductivity.

Multi-Nuclear Rare-Earth-Implanted Tartaric Acid-Functionalized Selenotungstates and Their Fluorescent and Magnetic Properties

A family of multinuclear rare-earth (RE)-implanted H₂tart^2--functionalized selenotungstates (STs) [H₂N(CH₃)₂]₁₃H{[W₂O₅(OH)₂(H₂tart)₂](H₂tart){[W₃O₆RE₂(H₂O)₆][SeW₉O₃₃]₂}₂}·31H₂O [RE = Eu³⁺ (1), Tb³⁺ (2), Dy³⁺ (3), Ho³⁺ (4), Y³⁺ (5); H₄tart = d-tartaric acid] have been afforded by a simple one-pot aqueous reaction and were structurally characterized. Intriguingly, their isomorphous organic-inorganic hybrid anion {[W₂O₅(OH)₂(H₂tart)₂](H₂tart){[W₃O₆RE₂(H₂O)₆][SeW₉O₃₃]₂}₂}^14- includes two sandwich-type {[W₃O₆[RE₂(H₂O)₆][SeW₉O₃₃]₂}^4- dimeric units with a W-O-RE heterometal core, which are further joined by two H₂tart^2--decorated dinuclear tungsten-oxo {W₂O₅(OH)₂(H₂tart)₂} clusters and a bridging H₂tart^2- ligand, contributing to a surprising Mobius band-like configuration. It is worth emphasizing that three H₂tart^2- ligands coordinate with tungsten centers rather than RE cations. For all we know, 1-5 delegate the infrequent RE-implanted STs functionalized by triplicate H₂tart^2- bridges. Furthermore, fluorescent performances of 1-4 as well as magnetic properties of 2-4 have been surveyed. The solid-state fluorescence emission spectra prove that each of them undoubtedly shows the characteristic emission peaks of RE cores, while alternating-current susceptibility measurements suggest field-induced single-molecule magnetic behavior in 3.

Inorganic–organic hybrid supramolecular architectures based on Keggin polyoxometalates and crown ether: synthesis, crystal structure and electrochemical properties

Novel supramolecular assemblies built from Keggin-type polyoxometalate and [18]-crown-6 ether building blocks exhibit unique propeller-like supramolecular host–guest structures.

Two novel nickel cluster substituted polyoxometalates: syntheses, structures and their photocatalytic activities, magnetic behaviors, and proton conduction properties

A Ni₁₂-substituted POM and a Ni₆-substituted POM have been synthesized and characterized. The compounds show a moderate catalytic activity in visible-light-driven CO₂ reduction reactions, and can serve as potential proton conduction materials.

Two highly stable inorganic–organic hybrid 3D frameworks based on Cu–Ln incorporated polyoxometalates for selective dye removal and proton conduction

Two highly stable inorganic–organic hybrid 3D TM–Ln incorporated POM-based framework materials have been successfully synthesized. The compounds can not only exhibit moderate proton conductivity but also selectively adsorb cationic dyes.

Proton conductive polyoxoniobate frameworks constructed from nanoscale {Nb68O200} cages

Nanoscale {Nb₆₈O₂₀₀} cages have been successfully employed as flexible and stable secondary building units to combine with bridging copper–amine complexes to construct two proton conductive polyoxoniobate frameworks, demonstrating a promising strategy for making new porous materials.

Chemistry of Metal Silicates and Germanates: The Largest Metal Polygermanate, K11Mn21Ge32O86(OH)9(H2O), with a 76 Å Periodic Lattice

An examination of manganese silicates and germanates revealed unusual structural motifs and extremely different chemistries, with identical hydrothermal reactions forming K₂Mn₂Si₃O₉ versus K₁₁Mn₂₁Ge₃₂O₈₆(OH)₉(H₂O). The germanate is exceptional in both its c-axis length (exceeding 76 Å) and unit cell volume (nearly 18000 ų), the largest known polygermanate structure to our knowledge.

Controlled Synthesis and Properties of 3d-4f Metals Co-doped Polyoxometalates-Based Materials

It is challenging to explore and prepare polyoxometalates-based nanomaterials (PNMs) with controllable morphologies and diversiform components. Herein, 3d-4f metals are introduced into isopolyoxometalates and Anderson-type polyoxometalates, CeCdW₁₂ nanoflower and EuCrMo₆ microflaky have been fabricated respectively. A series of control experiments are carried out to identify the impact factors on the rare morphologies in PNMs. Furthermore, upon excitation at 396 nm, the emission spectrum of EuCrMo₆ displays five prominent f - f emitting peaks at 674, 685, 690, 707, and 734 nm that are assigned to Eu^{3+ 5}D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions. Meanwhile, the VSM results show that the Cr⁺³ ions in EuCrMo₆ display anti-ferromagnetic interactions when the temperature is lower than - 17.54 K. After rising temperature, this material exhibits paramagnetic property. This work opens up strategies toward the brand new morphologies and components of PNMs, endowing this kind of material with new functions.

A New FeIII Substituted Arsenotungstate [FeIII2(AsIIIW6O23)2(AsIIIO3H)2]12−: Synthesis, Structure, Characterization and Magnetic Properties

The iron(III)-containing arsenotungstate [FeIII2(AsIIIW6O23)2(AsIIIO3H)2]12− (1) was prepared via a simple, one-pot reaction in aqueous basic medium. The compound was isolated as its sodium salt, and structurally-characterized by Single Crystal X-ray Diffraction (SCXRD), Powder X-ray Diffraction (PXRD), Fourier-Transform Infrared (FT-IR) spectroscopy, Thermogravimetric Analysis (TGA) and elemental analysis. Its magnetic properties are reported; the antiferromagnetic coupling between the two FeIII centers is unusually weak as a result of the bridging geometry imposed by the rigid arsenotungstate metalloligands.

Synthesis, Characterization, Electrochemistry, Photoluminescence and Magnetic Properties of a Dinuclear Erbium(III)-Containing Monolacunary Dawson-Type Tungstophosphate: [{Er(H2O)(CH3COO)(P2W17O61)}2]16−

Reaction of the trilacunary Wells−Dawson anion {α-P2W15O56}12− with ErIII ion in a 1 M LiOAc/HOAc buffer (pH 4.8) solution produces a dinuclear erbium(III) substituted sandwich-type structure [{Er(H2O)(CH3COO)(P2W17O61)}2]16− (1). The isolated compound was structurally characterized using single crystal and powder X-ray diffraction, FTIR spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical, electrocatalytic, photoluminescence and magnetic properties of 1 were investigated.

A trimeric tri-Tb3+ including antimonotungstate and its Eu3+/Tb3+/Dy3+/Gd3+-codoped species with luminescence properties

A trimeric tri-Tb3+-including antimonotungstate (AMT) hybrid Na17{(WO4)[Tb(H2O)(Ac)(B-α-SbW9O31(OH)2)]3}·50H2O (Tb3W28) was successfully synthesized, in which the capped tetrahedral {WO4} group plays a significant template role in directing the aggregation of three [B-α-SbW9O33]9- fragments and three Tb3+ ions. Eu3+/Tb3+/Dy3+/Gd3+-codoped AMT materials based on Tb3W28 were firstly prepared and their luminescence properties were investigated. The red emitter Eu3+, yellow emitter Dy3+, and nonluminous Gd3+ ions were codoped into Tb3W28 to substitute Tb3+ ions for investigating the energy transfer (ET) mechanism among Eu3+, Tb3+, and Dy3+ ions. Upon the 6H15/2 → 4I13/2 excitation at 389 nm of the Dy3+ ion, the ET1 mechanism (Dy3+ → Tb3+) was confirmed as a non-radiative dipole-dipole interaction. Under the 7F6 → 5L10 excitation at 370 nm of the Tb3+ ion, the ET2 mechanism (Tb3+ → Eu3+) was identified as a non-radiative quadrupole-quadrupole interaction. Under excitation at 389 nm, the two-step successive Dy3+ → Tb3+ → Eu3+ ET3 process was proved in Dy1.2Tb3zEu0.03Gd1.77-3zW28. Through changing the excitation wavelengths, the emission color of Dy1.2Tb1.2Eu0.03Gd0.57W28 can vary from blue to yellow, in which a near-white-light emission case was observed upon excitation at 378 nm. This work not only provides a systematic ET mechanism study of hetero-Ln-codoped AMTs, but also offers some useful guidance for designing novel performance-oriented Ln-codoped polyoxometalate-based materials.