Giant Hollow Heterometallic Polyoxoniobates with Sodalite-Type Lanthanide-Tungsten-Oxide Cages: Discrete Nanoclusters and Extended Frameworks

Giant Polyoxoniobate-Based Inorganic Molecular Tweezers: Metal Recognitions, Ion-Exchange Interactions and Mechanism Studies

This work reports the interesting and unique cation-exchange behaviors of the first indium-bridged purely inorganic 3D framework based on high-nuclearity polyoxoniobates as building units. Each nanoscale polyoxoniobate features a fascinating near-icosahedral core-shell structure with six pairs of unique inorganic "molecular tweezers" that have changeable openings for binding different metal cations via ion-exchanges and exhibit unusual selective metal-uptake behaviors. Further, the material has high chemical stability so that can undergo single-crystal-to-single-crystal metal-exchange processes to produce a dozen new crystals with high crystallinity. Based on these crystals and time-dependent metal-exchange experiments, we can visually reveal the detailed metal-exchange interactions and mechanisms of the material at the atomic precision level. This work demonstrates a rare systematic and atomic-level study on the ion-exchange properties of nanoclusters, which is of significance for the exploration of cluster-based ion-exchange materials that are still to be developed.

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.

An Unprecedented Bird Nest Molybdenum(V) Cobalto-Phosphate Nanosized Wheel Constructed from the [H55 (Mo24 O48 )(Co4 O)2 Co16 (PO4 )42 (py)6 (EtOH)2 (H2 O)11 ]3- Anion

An unprecedented bird-nest high-nuclear molybdenum(V) cobalto-phosphate nanosized wheel modified by imidazole (im) and pyridine (py), {[H₅₅ (Mo₂₄ O₄₈ )(Co₄ O)₂ Co₁₆ (PO₄ )₄₂ (py)₆ (EtOH)₂ (H₂ O)₁₁ ]- @[(Him)₂ (Hpy)]}(N-Et-py)(H₂ PO₄ )(py)₇ (EtOH)⋅12 H₂ O (1), has been successfully synthesized by self-assembly. The anionic huge wheel consists of two rare {Co₄ O} squares, four {Co₄ } tetramers, four {Mo₄ } tetramers and four {Mo₂ } dimers, linked by bridging oxygen atoms and [PO₄ ] groups and encloses two imidazolium cations and a protonated pyridium for charge balance. Surprisingly, 1 represents the first twisted wheel-shaped cluster with a record high-nuclear molybdenum(V) cobalto-phosphate. The delocalized electron effects of the cluster are enhanced with the help of coordinated py ligands, which endows 1 with an excellent third-order nonlinear optical (NLO) response. Additionally, 1 also shows a better photocatalytic water oxidation activity than Co(NO₃ )₂ with the O₂ production of 205 μmol during 6 h in the absence of the [Ru(bpy)₃ ]²⁺ photosensitizer.

Preparations, Structures and Luminescence Properties of Penta-rare-earth Incorporated Tetravacant Dawson Selenotungstates and Their Ho3+ /Tm3+ Co-doped Derivatives

A family of penta-rare-earth incorporated tetravacant Dawson selenotungstates [H₂ N(CH₃ )₂ ]₁₀ H₃ [SeO₄ RE₅ (H₂ O)₇ (Se₂ W₁₄ O₅₂ )₂ ] ⋅ 40H₂ O [RE=Ho³⁺ (1), Er³⁺ (2), Tm³⁺ (3), Tb³⁺ (4)] were synthesized. It should be noted that a penta-RE [SeO₄ RE₅ (H₂ O)₇ ]¹¹⁺ central core connecting two tetra-vacant Dawson-type [Se₂ W₁₄ O₅₂ ]^12- subunits generates a dimeric assembly of [SeO₄ RE₅ (H₂ O)₇ (Se₂ W₁₄ O₅₂ )₂ ]^13- in the structures of 1-4. Meanwhile, a class of Ho³⁺ /Tm³⁺ co-doped derivatives based on 1 with a Ho³⁺ /Tm³⁺ molar ratio of 0.75:0.25-0.25:0.75 were also prepared and characterized by energy-dispersive spectroscopy (EDS) analyses. Moreover, their luminescence properties were systematically investigated, which indicate that Tm³⁺ ions can sensitize the emission of Ho³⁺ ions in the visible region and prolong the fluorescence lifetime of Ho³⁺ ions to some extent. Energy transfer from Tm³⁺ ions to Ho³⁺ ions was probed by time-resolved emission spectroscopy (TRES), and the CIE 1931 diagram has been applied to evaluate all possible luminescence colors.

All-Inorganic Ionic Porous Material Based on Giant Spherical Polyoxometalates Containing Core-Shell K6 @K36 -Water Cage

This work demonstrates that the use of high-negative and high-symmetry lacunary polyoxometalates (POMs) for the clustering of alkali metal ions is a feasible strategy not only for the formation of rare high-nuclearity alkali-metal clusters but also for the construction of new-type all-inorganic ionic porous materials. By the strategy, an unprecedented high-nuclearity K-H₂ O cluster {K₄₂ (H₂ O)₆₀ } with core-shell K₆ @K₃₆ configuration is stabilized by 8 C_3v -symmetry trivacant POMs [GeW₉ O₃₄ ]^10- , forming a novel giant ionic alkali-metal-POM composite cluster {K₄₂ Ge₈ W₇₂ O₂₇₂ (H₂ O)₆₀ } with more than 100 metal centers. The incorporated 42-nuclearity K-H₂ O cluster {K₄₂ (H₂ O)₆₀ } exhibits the highest-nuclearity alkali-metal-water cluster known to date in POM chemistry. Further, the giant {K₄₂ Ge₈ W₇₂ O₂₇₂ (H₂ O)₆₀ } clusters can be linked by another kind of alkali metal ions Na⁺ to generate a fascinating three-dimensional all-inorganic ionic porous framework with high chemical stability, proton conductivity, and water vapor adsorption.

Exploring the Molecular Growth of Two Gigantic Half-Closed Polyoxometalate Clusters {Mo180 } and {Mo130 Ce6 }

Understanding the process of the self‐assembly of gigantic polyoxometalates and their subsequent molecular growth, by the addition of capping moieties onto the oxo‐frameworks, is critical for the development of the designed assembly of complex high‐nuclearity cluster species, yet such processes remain far from being understood. Herein we describe the molecular growth from {Mo₁₅₀} and {Mo₁₂₀Ce₆} to afford two half‐closed gigantic molybdenum blue clusters {Mo₁₈₀} (1) and {Mo₁₃₀Ce₆} (2), respectively. Compound 1 features a hat‐shaped structure with the parent wheel‐shaped {Mo₁₅₀} being capped by a {Mo₃₀} unit on one side. Similarly, 2 exhibits an elliptical lanthanide‐doped wheel {Mo₁₂₀Ce₆} that is sealed by a {Mo₁₀} unit on one side. Moreover, the observation of the parent uncapped {Mo₁₅₀} and {Mo₁₂₀Ce₆} clusters as minor products during the synthesis of 1 and 2 strongly suggests that the molecular growth process can be initialized from {Mo₁₅₀} and {Mo₁₂₀Ce₆} in solution, respectively.