A photoelectrochemical capacitor using polyoxometalates coupled with semiconductor nanocrystals as the photosensitizer

Solar energy storage technology ensures a sustainable and reliable energy supply. Herein, we show that electrons generated in semiconductor nanocrystals (NCs) of CsPbBr3 by visible light excitation can be stored in polyoxometalates (POMs) of W10O32, and extracted as an electric current using a photoelectrochemical cell.

Contrasting Trivalent Lanthanide and Actinide Complexation by Polyoxometalates via Solution-State NMR

Deciphering the solution chemistry and speciation of actinides is inherently difficult due to radioactivity, rarity, and cost constraints, especially for transplutonium elements. In this context, the development of new chelating platforms for actinides and associated spectroscopic techniques is particularly important. In this study, we investigate a relatively overlooked class of chelators for actinide binding, namely, polyoxometalates (POMs). We provide the first NMR measurements on americium-POM and curium-POM complexes, using one-dimensional (1D) ³¹P NMR, variable-temperature NMR, and spin-lattice relaxation time (T₁) experiments. The proposed POM-NMR approach allows for the study of trivalent f-elements even when only microgram amounts are available and in phosphate-containing solutions where f-elements are typically insoluble. The solution-state speciation of trivalent americium, curium, plus multiple lanthanide ions (La³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Yb³⁺, and Lu³⁺), in the presence of the model POM ligand PW₁₁O₃₉^7- was elucidated and revealed the concurrent formation of two stable complexes, [M^III(PW₁₁O₃₉)(H₂O)_x]^4- and [M^III(PW₁₁O₃₉)₂]^11-. Interconversion reaction constants, reaction enthalpies, and reaction entropies were derived from the NMR data. The NMR results also provide experimental evidence of the weakly paramagnetic nature of the Am³⁺ and Cm³⁺ ions in solution. Furthermore, the study reveals a previously unnoticed periodicity break along the f-element series with the reversal of T₁ relaxation times of the 1:1 and 1:2 complexes and the preferential formation of the long T₁ species for the early lanthanides versus the short T₁ species for the late lanthanides, americium, and curium. Given the broad variety of POM ligands that exist, with many of them containing NMR-active nuclei, the combined POM-NMR approach reported here opens a new avenue to investigate difficult-to-study elements such as heavy actinides and other radionuclides.

Spectrophotometric methods to probe the solution chemistry of lanthanide complexes with macromolecules

Lanthanide biochemistry has experienced a revival in recent years owing to the discovery of new biomolecular platforms that are amenable to bind, sequester, or transport lanthanide ions. This has inherently created a need for physicochemical methods that report on lanthanide-containing macromolecular systems. In this chapter, the use of spectrophotometric methods to study the stability of lanthanide-macromolecule complexes in solution is discussed. Indeed, lanthanide ions have unique spectral properties in the ultraviolet, visible, and near-infrared domains that set them apart from the more common elements encountered in biochemistry, and these unique features can be leveraged to study, in a quantitative and robust manner, the solution chemistry of their biorelevant species (K_d, pH stability, temperature profile, etc.). This chapter aims at bringing a method that has been established and validated in the small molecule chemistry field to this new era of lanthanide biochemistry.

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.

A Giant Mo/Ta/W Ternary Mixed-Addenda Polyoxometalate with Efficient Photocatalytic Activity for Primary Amine Coupling

The reactivity and properties of polyoxometalates (POMs) vary remarkably as a function of the kind of addenda atoms, so the design and synthesis of new mixed-addenda POMs is a promising approach for the further development of the POM-related areas. In the present work, the first Mo/Ta/W ternary mixed-addenda POM (NH₄)₄₁H₇[K₃(H₂O)₃(P₂W₁₅Ta₃O₆₂)₆(Mo₂O₄CH₃CO₂)₃(MoO₃)₂]·85H₂O (1), which is composed of 6 {P₂W₁₅Ta₃O₆₂} linked by 3 {Mo^V₂O₄(OOCCH₃)⁺} and 2 {Mo^VIO₃} via 18 novel Mo-O-Ta bridges has been synthesized. The precursor {P₂W₁₅Ta₃}, which has lower redox potential, is crucial for the formation of 1. The red-brown solid sample of 1 shows strong absorption in the visible region. The visible-light responsive charge transfer from benzylamine to 1 was observed experimentally. 1 was proved to be an efficient photocatalyst under simulated sunlight (AM 1.5G) radiation for the oxidative coupling of primary amines to imines using atmospheric O₂.

Niobium uptake by a [P8W48O184]40−macrocyclic polyanion

Incorporation of Nb into the [P₈W₄₈O₁₈₄]⁴⁰⁻anionic macrocyclic cavitand leads to formation of new Nb–W POMs. Inclusion of up to five {NbO(H₂O)}³⁺groups was observed. Solution speciation of the Nb-encapsulating macrocycles was studied by HPLC-ICP-AES and SAXS.

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.

Self-assembly of [PNbxW12−xO40]n− Keggin anions – a simple way to mixed Nb–W polyoxometalates

This paper summarizes preparations of mixed phosphoniobotungstates [PNb_xW_12−xO₄₀]^(3+x)− (x = 1–3) based on two different ways: incorporation of Nb into pre-existing lacunary-type phosphotungstates and self-assembly reactions.

Lanthanide derivatives of Ta/W mixed-addendum POMs as proton-conducting materials

Four lanthanide derivatives were isolated by the self-assembly of {P₂W₁₅Ta₃O₆₂} and lanthanide ions, which showed good proton conduction performance.

Electronic and relativistic contributions to ion-pairing in polyoxometalate model systems

Experiment and theory delineate covalency, electrostatic association, and relativistic effect contributions to polyoxometalate-alkali ion-pairs in water.

Extraction of Nb(v) by quaternary ammonium-based solvents: toward organic hexaniobate systems

Solvent extraction of Nb(v) from alkaline aqueous media using quaternary ammonium solutions, especially Aliquat® 336 diluted in an aliphatic diluent, was investigated. The hexaniobate ions (H_xNb₆O₁₉^x-8) were extracted into the organic phase with very high yields at room temperature and within a few minutes, affording easy access to organic solutions of hexaniobates. Several parameters were found to influence the extraction of H_xNb₆O₁₉^x-8 including the nature and concentration of alkali cations, confirming subtle effects previously described for polyoxoniobates such as ion-pairing with alkali ions. The extraction of H_xNb₆O₁₉^x-8 with Aliquat® 336 is also influenced if competing anions are present in the aqueous phase (NO₃^-, Cl^-, C₂O₄^2-, SO₄^2- and CO₃^2-) and varies with the pH mainly due to the competitive extraction of hydroxide ions at high pH. The co-extraction of sodium ions with H_xNb₆O₁₉^x-8 was observed as well as the co-extraction of water molecules, suggesting a self-association of the extractant. The proposed liquid-liquid extraction generic system paves the way for innovative niobium (and potentially tantalum) hydrometallurgical processes and it may also afford more direct routes for exploring the chemistry of hexaniobates in organic solvents.

Cesium salts of niobo-tungstate isopolyanions with intermediate group V–group VI character

The physical and electronic structures of cesium salts of niobo-tungstate Lindqvist ions vary with Nb content, elucidated experimentally and computationally.