Unprecedented {Fe14 }/{Fe10 } Polyoxotungstate-Based Nanoclusters with Efficient Photocatalytic H2 Evolution Activity: Synthesis, Structure, Magnetism, and Electrochemistry

Three Double-Layered {Ni8}@{Bn}2 (n = 3, 4, 6) Cluster Sandwiched Polyoxometalates

The reaction of [A-α-GeW9O34]10- with Ni2+ in the presence of inorganic boron sources yielded three unprecedented sandwiched Ni-added polyoxometalates (NiAPs): K6Na7H7[({Ni8(μ6-O)(OH)2}@{B3O6(OH)3}2)@(B-α-GeW9O34)2]·16H2O (1), K4Na4H12[({Ni8(μ6-O)}@{B4O8(OH)3}2)@(B-α-GeW9O34)2]·16H2O (2), and K10Na6[({Ni8(μ6-O)}@ {B6O9(OH)5}2)@(B-α-GeW9O34)2]·12H2O (3). The common feature of 1-3 is that a rare double-layered {Ni8}@{Bn}2 (n = 3,4,6) cluster is inlaid in their sandwich belts. The {Ni8} cluster is composed of two cubane {Ni4} clusters by six bridging oxygen atoms and sharing a μ6-O atom. The numbers of boron atoms in the {Ni8}@{Bn}2 (n = 3,4,6) clusters of 1-3 are different, namely, {Ni8}@{B3}2, {Ni8}@{B4}2, and {Ni8}@{B6}2 clusters. To the best of our knowledge, such architectures containing a double-layered {Ni8}@{Bn}2 (n = 3,4,6) cluster in the sandwich belts are the first observed in POM chemistry. Furthermore, 2 was investigated as an efficient heterogeneous catalyst for the Knoevenagel condensation of various aldehydes with malononitrile at room temperature.

Physico- and Electrochemical Properties of First-Row Transition-Metal-Substituted Sandwich Polyoxometalates

The physico- and electrochemical behaviors of a series of [WZn₃(H₂O)₂(ZnW₉O₃₄)₂]^12- (Zn-WZn₃) and its first-row transition-metal-substituted analogues [WZn(TM)₂(H₂O)₂(ZnW₉O₃₄)₂]^12- (Zn-WZn(TM)₂; TM = Mn^II, Co^II, Fe^III, Ni^II and Cu^II) are reported. Various spectroscopic studies, including Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, electrospray ionization (ESI)-mass spectrometry, and Raman spectroscopy, show similar spectral patterns in all sandwich polyoxometalates (POMs) because of their isostructural geometry and constancy of the overall negative charge (-12). However, the electronic properties highly depend on the transition metals at the "sandwich core" and correlate well with the density functional theory (DFT) study. Further, depending on the substituted TM atoms, there is a decrease in the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) band-gap energy in these transition-metal-substituted POM (TMSP) complexes wrt Zn-WZn₃, as confirmed by diffuse reflectance spectroscopy and DFT study. Cyclic voltammetry reveals that the electrochemistry of these sandwich POMs (Zn-WZn₃ and TMSPs) is highly dependent on the pH of the solution. Moreover, the dioxygen binding/activation studies of these polyoxometalates show that Zn-WZn₃ and Zn-WZnFe₂ have better efficiency toward dioxygen binding, as confirmed by FTIR spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA), which is also reflected in their catalytic activity toward imine synthesis.

High-Nuclear Ni-Substituted Poly(polyoxometalate) Containing an Anderson-like {Cs7} Cluster

A novel high-nuclear Ni-substituted poly(polyoxometalate) [poly(POM)], [H₂N(CH₃)₂]₂Na₁₈Cs₂H₁₃[(Cs₇(H₂O)₆)@{(PO₄)-@(Ni₄(OH)₃(WO₄))₃@(B-α-PW₉O₃₄)₃}₂]·30H₂O (1), has been successfully developed and structurally characterized. The polyoxoanion of 1 can be viewed as a unique huge sandwich structure made of an unprecedented Cs₇(H₂O)₆ ({Cs₇}) cluster core encapsulated by two trimeric [(PO₄)@(Ni₄(OH)₃(WO₄))₃@(B-α-PW₉O₃₄)₃]^21- subunits, in which the {Cs₇} cluster presents an interesting Anderson-like arrangement and is the first example of a classical POM configuration based on the alkali metal cluster in the POM chemistry. The polyoxoanion can also be described as an unusual [(Cs₇(H₂O)₆)@{(PO₄)@(Ni₄(OH)₃(WO₄))₃}₂]¹⁹⁺ cluster packaged by six {PW₉} fragments. Furthermore, investigations on the Knoevenagel condensation reaction reveal that 1 has good catalytic activity for the condensation of various aldehydes and malononitrile into corresponding products with excellent yields.

Two Ni-Substituted Trilacunary Keggin-Type Polyoxometalates: Syntheses, Crystal Structures, NLO Studies, and Magnetic Properties

Two Ni-substituted polyoxometalates (NiSPs), [Ni₆(Py)₆(H₂O)₅(μ₃-OH)₃(PW₉O₃₄)]₂·10H₂O (1), [Ni₇(Py)₆(Im)(H₂O)₅O(WO₄)(μ₃-OH)₃(H₂PW₉O₃₄)]·3H₂O (2) (Py = pyridine, Im = imidazole), were successfully hydrothermally synthesized. Compounds 1 and 2 have significantly different configurations by introducing different amounts of imidazole ligands. For compound 1, two malposed {Ni₆(Py)₆PW₉} units that are face to face are bridged by two Ni-O-W bonds to constitute an isolated dimeric structure. Differently, the {Ni₇(Py)₆(Im)PW₉}₂ dimer in compound 2 connects with four adjacent dimers by four {WO₄} groups in an interesting two-dimensional (2-D) arrangement. The magnetism of compounds 1 and 2 was studied, and magnetic test results demonstrated that both compounds have ferromagnetic interactions between the nickel centers. Meanwhile, the third-order nonlinear optical (NLO) measurements indicated that compound 1 can serve as potential nonlinear optical materials.

Lacunary {Se4V10} Heteropolyoxovanadate Precursor with Monometal, Metal-Richer-Sandwiched Derivatives {Se8V20M} and {Se8V20M3}: Correlations between the Synthesis, Structure, and Catalytic Property

A new family of trinuclear transition-metal (TM)-sandwiched heteropolyoxovanadates (hetero-POVs) [(SeV₁₀O₂₈(SeO₃)₃M(H₂O)₃)₂(M(H₂O)₄)]^10- (Se₈V₂₀M₃, where M = Mn²⁺, Co²⁺, and Zn²⁺) were prepared using two feasible approaches: a stepwise assembly strategy atop the POV precursor Se₄V₁₀ and a one-pot reaction approach of KVO₃, SeO₂, TM²⁺, and a proline ligand. The crystallographic studies reveal that Se₈V₂₀M₃ consist of two asymmetric [SeV₁₀O₂₈(SeO₃)₃M(H₂O)₃)]^6- units, linked by another TM²⁺ ion, thus forming an interesting staggered sandwich-type arrangement. Additionally, Se₈V₂₀M₃ and Se₈V₂₀M present strong correlations between their structures and catalytic properties. In particular, Se₈V₂₀M₃ demonstrate an analogical heterogeneous catalytic performance as Se₈V₂₀M in the sulfoxidation reaction of thioethers owing to their structural similarities.

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.

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.

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.

Selenotungstates incorporating organophosphonate ligands and metal ions: synthesis, characterization, magnetism and catalytic efficiency in the Knoevenagel condensation reaction

Three new sandwich-type selenotungstate anion structures and Co1 show superior catalytic performance in the Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate under mild conditions.

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.

Preparation, characterization and electrocatalysis performance of a trimeric ruthenium-substituted isopolytungstate

The ruthenium-containing isopolytungstate Rb₁₀K₃H₆[SeO₃(H₉Ru_5.5W_30.5O₁₁₄)]Cl₃·48H₂O was isolated and then served as a catalyst, showing electrochemical catalytic activity towards the oxidation reaction of nitrite.

A multilayer assembly of two mixed-valence Mn16-containing polyanions and study of their electrocatalytic activities towards water oxidation

Herein, two mixed-valence Mn16-containing polyanions, (Mn16) [MnIII10MnII6O6(OH)6(PO4)4(A-a-SiW9O34)4]28- (Mn16-Cs) and [MnIII4MnII12(OH)12(PO4)4(A-a-SiW9O34)4]28- (Mn16-Rb), were successfully fabricated on an indium tin oxide (ITO)-coated glass electrode and a glass carbon electrode (GCE) by a layer-by-layer assembly method. Moreover, four composite films, i.e. [PDDA/Mn16-Cs]n, [PDDA/Mn16-Rb]n, [Mn16-Cs/Rubpy]n, and [Mn16-Rb/Rubpy]n (PDDA: poly(diallyldimethylammonium chloride); Rubpy: tris(2,2'-bipyridyl)ruthenium(ii) chloride; n = 1-10), were constructed for comparison and characterized by UV-visible spectroscopy, cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic activities towards water oxidation were studied under the same experimental conditions. The results of the controlled experiments indicate that (1) all the four films exhibit expected electrocatalytic activities towards water oxidation; (2) the electrocatalytic activity of Mn16-Cs is better than that of Mn16-Rb in solution and composite films; and (3) the electrocatalytic activities of the composite film [Mn16/Rubpy]n are better than those of the composite film [PDDA/Mn16]n.

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.

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.