Synthesis and Characterization of [(OH)TeNb5O18](6-) in Water Solution, Comparison with [Nb6O19](8-)

Indium-Assisted Construction of {SiNb18O54}-Based Aggregates and Their Assembly into Extended Polyoxoniobate Architectures

In this research, indium ions were introduced into polyoxoniobates (PONbs) reaction systems to facilitate the construction of different {SiNb18O54}-based aggregates, including an {In(en)2{SiNb18O54}2} (en = ethylenediamine) dimer, an {[InO2][In2(en)O3]2{SiNb18O54}3} trimer, and an {[In(en)2][InO2][In7(en)5O9]{SiNb18O54}4} tetramer. Interestingly, these aggregates were further assembled into three uncommon extended PONb architectures in the presence of [Cu(en)2]2+ complexes, namely, H3[Cu(en)2(H2O)][Cu(en)2]6[Cu(en)2]2{[In(en)2][K2{SiNb18O54}(H2O)6]2}·1.5en·16H2O, H9{[Cu(en)2]6{[Cu(en)2]3[Cu(en)2(H2O)][In(H2O)2][In2(en)(H2O)2(OH)]2{SiNb18O54}3}·5en·29H2O, and H14[Cu(en)2]0.5[Cu(en)2(H2O)]{[Cu(en)2]2{[Cu(en)2]3[Cu(en)2(H2O)]5[K(H2O)2][In(H2O)2][In(en)2][In7(OH)9(en)5]{SiNb18O54}4}·7en·39H2O. In addition, all of them have good water vapor adsorption capacities and moderate proton transport capabilities. The above results indicate that introducing suitable heteroatoms to induce the aggregation PONb building blocks and further assembling them into new structures is an effective strategy to enrich the PONbs' structural diversity and develop new functional materials.

An Organodiphosphate-Containing Polyoxoniobate Ring and Its Assembly into a Three-Dimensional Framework through Hydrogen Bonding

In this work, a novel organodiphosphate-containing inorganic-organic hybrid polyoxoniobate (PONb) ring {(PO3CH2CH2PO3H)4Nb8O16}4- (Nb8P8) has been achieved by a one-pot hydrothermal method. The ring is constructed from a tetragonal {Nb8O36} motif and four {PO3CH2CH2PO3H} ligands. Interestingly, Nb8P8 can be joined together via K-H2O clusters {K2(H2O)4(OH)2} to form one-dimensional chains {[K2(H2O)4(OH)2]Nb8P8}n and further linked by {Cu(en)2}2+ (en = ethylenediamine) complexes, resulting in a three-dimensional supramolecular framework {[Cu(en)2]2[K2(H2O)4(OH)2]Nb8P8}·3en·H2O (1). 1 exhibits good chemical and thermal stability and has a high water vapor adsorption capacity of ≤224 cm3 g-1 (22.71 mol·mol-1) at 298 K, outperforming most of the known polyoxometalate-based materials. Impedance measurements prove that 1 can transfer protons with moderate conductivity. This study not only contributes to the structural diversity of organodiphosphate-containing PONbs and PONb rings but also provides a reference for the development of PONb-based materials with unique performance.

Not So Similar: Different Ways of Nb(V) and Ta(V) Catecholate Complexation

The reactions between catechol (H₂cat) and niobium(V) or tantalum(V) precursors in basic aqueous solutions lead to the formation of catecholate complexes of different natures. The following complexes were isolated and characterized by single-crystal X-ray diffraction (SCXRD): (1) (NH₄)₃[NbO(cat)₃]∙4H₂O; (2) K₂[Nb(cat)₃(Hcat)]·2H₂cat·2H₂O; (3) Cs₃[NbO(cat)₃]·H₂O; (4) (NH₄)₄[Ta₂O(cat)₆]·3H₂O; (5) Cs₂[Ta(cat)₃(Hcat)]·H₂cat; (6) Cs₄[Ta₂O(cat)₆]·7H₂O. The isolated crystalline products were characterized by elemental analysis, X-ray powder diffraction (XRPD), FTIR, and TGA. The structural features of these complexes, such as {Ta₂O} unit geometry, Cs-π interactions, and crystal packing effects, are discussed.

Rocket-Shaped Telluroniobate with Efficient Catalytic Activity in the Transesterification Reaction

A novel telluroniobate, K₈Na₆H₇{[Co(en)₂(SO₃)][Te₄Nb₂₄O₇₉]}·42H₂O (en = ethylenediamine), has been synthesized through a diffusion strategy. It consists of a heteropolyoxoniobate [B-β-TeNb₉O₃₃]^17- cluster and isopolyoxoniobate {Nb₇O₂₂} building blocks. In addition, its structure was fully characterized by a series of spectroscopic methods. Furthermore, it exhibits an efficient catalytic performance in the transesterification of ethylene carbonate and methanol to prepare dimethyl carbonate with good catalytic reusability. Also, it demonstrates interesting proton conduction properties, with conductivity achieved at 3.05 × 10^-4 S cm^-1 (60 °C, 75% relative humidity).

All-inorganic ferric wheel based on hexaniobate-anion linkers

Utilizing the inherent ability of Lindquist-type hexaniobate cluster-anions, [Nb₆O₁₉]^8-, to serve as oxo-donor ligands in complexes with transition-metal cations, we report the synthesis and characterization of the first all-inorganic "ferric" wheel, Li₄₈[(Nb₆O₁₉)₈Fe₈(OH)₈]·88H₂O, comprised of eight Fe atoms linked by eight hexaniobate cluster-anion ligands. Bond valence sum analysis of the X-ray structure and the synthesis conditions themselves indicate that the Fe atoms are in the +3 oxidation state. This is confirmed by magnetic susceptibility and electron paramagnetic resonance (EPR) measurements which indicate the presence of high spin (S = 5/2) Fe(III) ions. In addition, magnetic susceptibility measurements reveal long-range superexchange antiferromagnetic interactions between the hexaniobate-ligand separated Fe³⁺ ions (J = -0.22 cm^-1). More generally, the results suggest the use of hexaniobate cluster-anions as linkers in the synthesis of other two- or three-dimensional polyoxometalate framework structures.

A Tellurium-Substituted Heteropolyniobate with Unique π-π Stacking and Ionic Conduction Property

A tetratellurium-substituted heteropolyoxoniobate with the formula K₂H[Cu(phen)(H₂O)]₄[Cu(phen)]₂[(LiNb₈Te₄O₄₀)]·34H₂O (1; phen = 1,10-phenanthroline) was hydrothermally prepared and structurally characterized. The compound represents the first hexavalent tellurium-substituted Keggin-type polyoxometalate (POM) so far. What is more, the POM cluster in 1 can elaborately self-assemble into a stable supramolecular framework with an ion conduction property through unique intermolecular π-π stacking.

Interactions of aromatic rings in the crystal structures of hybrid polyoxometalates and Ru clusters

Computational analysis for π–π interaction energies of {(arene)Ru}2+ containing complexes and relative group 5 hybrid polyoxometalates reveals different frameworks. Some perspectives on πOF materials processing and crystal engineering were discussed.

A comprehensive approach providing a new synthetic route for bimetallic electrocatalysts via isoPOMs [M/Rh(Cp*)4W8O32] (M = Rh (1) and Ir (2))

Polyoxometalates (POMs) are highly versatile materials if paired with various conducting supports. We here present a new prospective approach for obtaining advanced electrocatalytic systems via POMs (1 and 2) nanostructured on Ni foam (NF) to give bimetallic nanohybrid composite materials M0.4Ni0.6/WO3 (M = Rh (3) or Ir (4)). By this pathway, two rare isopolyoctatungstate-based organometallic clusters [Hx(MCp*)4W8O32]·yH2O (in 1, M = Rh, x = 8, y = 23; in 2, M = Ir, x = 4, y = 17.33) have been synthesized via one-pot reactions using [Cp*MCl2]2 (Cp* = pentamethylcyclopentadienyl, M = Rh or Ir) and Na2WO4·2H2O in basic conditions. Compounds 1 and 2 were successfully nanostructured on the surface of commercially available NF and were thermally reduced to M0.4Ni0.6/WO3 (M = Rh (3) or Ir (4)) after annealing at 400 °C for 8 h in a 15% H2/N2 atmosphere. Electrodes modified with the POMs 3 and 4 exhibited remarkable HER activities in a 1 M KOH solution and achieved a current density of 10 mA cm-2 at low overpotentials of about 67 and 35 mV versus RHE, with Tafel slopes of 56 and 34 mV dec-1, respectively.

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.

Redox Exfoliation of Layered Transition Metal Dichalcogenides

Transition metal dichalcogenides (TMDs) have attracted considerable attention in a diverse array of applications due to the breadth of possible property suites relative to other low-dimensional nanomaterials (e.g., graphene, aluminosilicates). Here, we demonstrate an alternative methodology for the exfoliation of bulk crystallites of group V-VII layered TMDs under quiescent, benchtop conditions using mild redox chemistry. Anionic polyoxometalate species generated from edge sites adsorb to the TMD surface and create Coulombic repulsion that drives layer separation without the use of shear forces. This method is generalizable (MS₂, MSe₂, and MTe₂) and effective in preparing high-concentration (>1 mg/mL) dispersions with narrow layer thickness distributions more rapidly and with safer reagents than alternative solution-based approaches. Finally, exfoliation of these TMDs is demonstrated in a range of solvent systems that were previously inaccessible due to large surface energy differences. These characteristics could be beneficial in the preparation of high-quality films and monoliths.

Unique solubility of polyoxoniobate salts in methanol: coordination to cations and POM methylation

In methanolic solutions of A₄[{LM′}₂M₆O₁₉] ({LM′} = {Cp*Rh}²⁺, {Cp*Ir}²⁺, {(C₆H₆)Ru}²⁺; M = Nb, Ta; A = Na, K) formation of methoxo complexes [{LM′}₂M₆O_19−n(OMe)n] (n = 1–3) and coordination of CH₃OH to A⁺ take place.