Poly(polyoxotungstate)s with 20 Nickel Centers: From Nanoclusters to One-Dimensional Chains

A Hexadecanuclear Cobalt-Added Tungstogermanate Containing Counter Cobalt Hydrates: Synthesis, Structure and Photocatalytic Properties

The synthesis and exploration of the properties of structurally-new polyoxometalates (POMs) has been attracting considerable research interest. In this work, a hexadecanuclear cobalt-added tungstogermanate, H₃₁(NH₄)₅Na₁₆{Co^Ⅲ(H₂O)₆}₄{[Co^Ⅱ₄(μ₃-OH)₃(PO₄)]₄(A-α-GeW₉O₃₄)₄}₂·23-H₂O (1), was synthesized under hydrothermal conditions and characterized by various techniques. Compound 1 can effectively drive the heterogeneous photocatalytic hydrogen evolution reaction in the presence of [Ir(ppy)₂(dtbbpy)][PF₆] as the photosensitizer, with triethanolamine (TEOA) and N-Hydroxy succinimide (NHS) used as the dual sacrificial reagents. Control experiments revealed the important role of NHS in enhancing the hydrogen-evolution activities. Under optimal catalytic conditions, a hydrogen yield of 54.21 μmol was achieved after 10-h photocatalysis, corresponding to a hydrogen evolution rate of 1807.07 μmol·g^-1·h^-1. Stability studies demonstrated that catalyst 1 can be isolated and reused for three successive photocatalytic cycles with negligible decline of the H₂ yield, indicating the stability and recycling robustness of catalyst 1.

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.

Ligand-Controlled Assembly of Heteropolyoxomolybdates from Plenary Keggin Germanomolybdates and Cu-Ln Heterometallic Units

By virtue of combining an in-situ assembly process with a stepwise synthesis in conventional aqueous solution, two series of unique organic-inorganic hybrid heteropolyoxomolybdates were constructed from plenary Keggin germanomolybdates and Cu-Ln heterometallic units and fully characterized: [H₂ INA]₂ H₈ [LnCu(INA)₄ (H₂ O)₆ ]₂ [α-GeMo₁₂ O₄₀ ]₃ ⋅52 H₂ O (Ln=La³⁺ (1), Ce³⁺ (2), Pr³⁺ (3), Nd³⁺ (4), Sm³⁺ (5), Eu³⁺ (6); HINA=isonicotinic acid) and (NH₄ )[Cu(PA)₂ ][Cu(PA)₂ Ln(H₂ O)₈ ][α-GeMo₁₂ O₄₀ ]⋅10 H₂ O (Ln=Nd³⁺ (7), Sm³⁺ (8), Eu³⁺ (9); HPA=picolinic acid). The most remarkable structural characteristic of compounds 1-6 was that their molecular units were defined by three discrete plenary Keggin [α-GeMo₁₂ O₄₀ ]^4- polyoxoanions and two organic-inorganic hybrid heterometallic [LnCu(INA)₄ (H₂ O)₆ ]⁺ moieties, whereas compounds 7-9 exhibited a nice-looking 1D chain-like structure that was built from plenary [α-GeMo₁₂ O₄₀ ]^4- polyoxoanions, pendent [Cu(PA)₂ ] complexes, and bridging {[Cu(PA)₂ ][Ln(H₂ O)₈ ]}³⁺ heterometallic groups. Notably, two different pyridine carboxylic acid ligands led to the discrepancy between the two structure types. To the best of our knowledge, compounds 1-9 constitute the first examples of plenary Keggin heterometallic germanomolybdates that include Cu-Ln-organic subunits. Further studies revealed that compounds 3 and 8 exhibited fast adsorption capacity for cationic dyes methylene blue (MB) and rhodamine B (RhB) in water. Moreover, compounds 3 and 8 could quickly and selectively adsorb MB from a mixture of MB/methyl orange (MO) or MB/azophloxine (Apo).

Polyoxotungstates incorporated organophosphonate and nickel: synthesis, characterization and efficient catalysis for epoxidation of allylic alcohols

“Top-down” synthetic strategy was performed to incorporate nickel into the organophosphonate-based POTs showing superior catalysis for the epoxidation of allylic alcohols.