A novel Ta/W mixed-addendum polyoxometalate with photocatalytic properties

Synthesis, crystal structure and selected properties of K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O

The new compound K2[Ni(dien)2]{[Ni(dien)]2Ta6O19}·11 H2O crystallized at room temperature applying a diffusion based reaction in a H2O/DMSO mixture using K8{Ta6O19}·16 H2O, Ni(NO3)2·6H2O and dien (diethylenetriamine). In the crystal structure, the Lindqvist-type anion [Ta6O19]8– is structurally expanded by two octahedrally Ni2+-centered complexes via three Ni–µ 2-O–Ta bonds thus generating the new {[Ni(dien)]2Ta6O19}4– anion. Two KO8 polyhedra share a common edge to form a K2O14 moiety, which connects the {[Ni(dien)]2Ta6O19}4– cluster shells into chains. The isolated [Ni(dien)2]2+ complexes are located in voids generated by the structural arrangement of the chains. An extended hydrogen bonding network between the different constituents generates a 3D network. The crystal water molecules can be thermally removed to form a highly crystalline dehydrated compound. Partial water uptake leads to the formation of a crystalline intermediate with a reduced unit cell volume compared to the fully hydrated sample. Water sorption experiments demonstrate that the fully dehydrated sample can be fully reconverted to the hydrated compound. The crystal field splitting parameters for the octahedrally coordinated Ni2+-centered complexes have been evaluated from an UV/Vis spectrum yielding D q = 1056 cm−1 and B = 887 cm−1.

Exploring the Coordination Modes of a Keggin-Type [ZnW12O40]6- Anionic Cluster: Bonding Patterns, Crystal Structure, and Semiconducting Properties

Polyoxometalate-based organic-inorganic hybrid compounds (POIHCs) have been greatly developed due to their wide application prospects, but the pursuit of their directed synthesis via molecular design still remains a challenge. Herein, we demonstrate that the coordination modes of the Keggin-type [ZnW₁₂O₄₀]^6- anion can be tuned, which leads to different semiconductor characteristics. Using the same building block, ligand, and metal ion (ZnW₁₂, phen, Cu²⁺), we synthesized three new POIHCs with different bonding patterns by means of different coordination modes of ZnW₁₂. The three POIHCs (H₂phen){ZnW₁₂O₄₀[Cu(phen)₂]₂}·3H₂O (1), {ZnW₁₂O₄₀[Cu(phen)(H₂O)₂]₂[Cu(phen)(H₂O)]}_n·3H₂O (2), and (Me₄N)₂{ZnW₁₂O₄₀[Cu(phen)(H₂O)]₂}_n·5H₂O (3) (phen = 1,10-phenanthroline) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a zero-dimensional coordination complex cluster, while compounds 2 and 3 are both 1D chain structures with different Cu²⁺ bridge linkages. Although these three POIHCs possess the same chemical components, their semiconductor properties are different, which is demonstrated by measurements of transient photocurrent and band gap (E_g) values. Furthermore, we carried out comparative experiments on the photoconductivity performance of compounds 1-3 and their photocatalytic reduction from O₂ to H₂O₂, indicating the significant influence of the energy level matching on the photocatalytic activity.

Visible-light-driven hydrogen evolution using a polyoxometalate-based copper molecular catalyst

[Cu₅(OH)₄(H₂O)₂(A-α-SiW₉O₃₃)₂]¹⁰⁻ (1) was tested as a molecular catalyst for visible-light-driven H₂ evolution and exhibited a high TON of 718.9. Many stability studies showed that 1 could maintain its structure intact during the catalytic process.

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.

New pronounced progress in the synthesis of group 5 polyoxometalates

This highlight summarizes new developments made in group 5 polyoxometalate science of high nuclearity clusters with focus on synthetic approaches.

Photocatalytic decolorization of three commercial dyes using a new heteropolyoxotantalate catalyst

The decolorization of commercial dyes is still a pertinent issue since these azo dyes are relatively resistant to conventional biological treatment methods. It is well known that polyoxometalates can absorb light in UV-Vis range that delivers electrons to the reducible species resulting in the decomposition of organic compounds. In this paper, we present the third heteropolyoxotantalate under conventional synthetic conditions in the presence of hydrogen peroxide. The compound has been thoroughly characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis and powder X-ray diffraction. The polyanion incorporates two 3-peroxotantalo-2-phosphate clusters that are linked together by four oxygen bridges. In addition, the photocatalytic activities of the title compound 1a were investigated. After 270 min irradiation, about 90% of Rhodamine B (RhB) was removed in the presence of 1a while the degradation of RhB could be negligible in the absence of 1a, indicating it can be a promising catalyst candidate for decolorization of organic dyes. Also, photocatalytic experiment for hydrogen generation was studied, and the results show that the H2 evolution rate is 3383 µmol h-1 g-1 for compound 1a (100 mg) over 6 h with the corresponding turnover number of 432.

Combined HPLC-ICP-AES technique as an informative tool for the study of heteropolyniobates

This paper summarizes the application of the coupled HPLC-ICP-AES technique to study the substitution of niobium by tungsten in [Nb₆O₁₉]⁸⁻ or [(OH)TeNb₅O₁₈]⁶⁻ Lindqvist anions and the screening of mixed [PMo_12−xNb_xO₄₀]ⁿ⁻ Keggin anion formation.

Dimethyltin-functionalized cyclic selenotungstates based on {Se2W12} units

Two dimethyltin-functionalized cyclic selenotungstates based on {Se₂W₁₂} units were obtained, where (CH₃)₂Sn²⁺ moieties were first introduced into “pure” POMs wheels.