Recent advances in isopolyoxotungstates and their derivatives

Synthesis and structural characterization of a hydrated sodium-caesium tetra-cosa-tungstate(VI), Na5Cs19[W24O84]·21H2O

Crystal formation of penta-sodium nona-deca-cesium tetra-cosa-tungstate(VI) heneikosahydrate, Na5Cs19[W24O84]·21H2O, was successfully achieved by the conversion of [H2W12O42]10- through the addition of excess Cs+. The crystal structure comprising the toroidal isopolyoxidometalate is presented, as well as its Raman spectrum. Na5Cs19(H2O)21W24O84 crystallizes in the rhombohedral space group R with an obverse centering. The title compound represents the addition of a new member to the isopolytungstate family with mixed alkali counter-ions and contains rarely observed five-coordinate tungsten(VI) atoms in the [W24O84]24- anion (site symmetry C 3i ) arising from the conversion mediated by Cs+ counter-ions.

The Smallest Polyoxotungstate Retained by TRIS-Stabilization

A polycondensation reaction of the orthotungstate anion WO₄^2–, buffered at pH 7.5 in a TRIS-HCl (0.15 M) solution, results in the first example of a discrete polyoxotungstate anion, with just two W ions stabilized with TRIS ligands. It was isolated and characterized as Na₂[W^VI₂O₆(C₄O₃NH₁₀)₂]·6H₂O by single-crystal and powder X-ray diffraction, FT-IR spectroscopy, thermogravimetrical analysis (TGA), and elemental analysis in solid state and by electro-spray ionization mass spectrometry (ESI-MS), ¹³C, and ¹⁸³W NMR, as well as Raman spectroscopy in solution. This synthesis demonstrates the crucial and new role of the added tris-alkoxy ligand in the development of a new hybrid TRIS-isopolytungstate with the lowest known nuclearity (so far) and the terminal oxygens substituted with two nitrogen atoms arising from amines of the TRIS ligands.

We report on the synthesis and characterization of a new hybrid isopolytungstate Na₂[W^VI₂O₆(C₄O₃NH₁₀)₂]·6H₂O with the, so far, lowest known nuclearity and the terminal oxygen atoms substituted with nitrogen arising from amine.

Interweaving Disciplines to Advance Chemistry: Applying Polyoxometalates in Biology

This Viewpoint brings awareness of the challenges and subsequent breakthroughs at the intersection of different disciplines, illustrated by the example of the influence biological entities exerted on a huge class of inorganic coordination compounds, called polyoxometalates (POMs). We highlight the possible effects of biological systems on POMs that need to be considered, thereby emphasizing the depth and complexity of interdisciplinary work. We map POMs’ structural, electrochemical, and stability properties in the presence of biomolecules and stress the potential challenges related to inorganic coordination chemistry carried out in biological systems. This Viewpoint shows that new chemistry is available at the intersections between disciplines and aims to guide the community toward a discussion about current as well as future trends in truly interdisciplinary work.

We discuss the investigation of polyoxometalates in biological systems as one future direction of chemistry. Highly interesting, new, and sometimes spectacular findings and applications can be obtained from correctly carried out interdisciplinary research. In this Viewpoint, the challenges of truly interdisciplinary work and concepts for overcoming boundaries while working on intertwining disciplines are discussed.

(Me2NH2)10[H2-Dodecatungstate] polymorphs: dodecatungstate cages embedded in a variable dimethylammonium cation + water of crystallization matrix

Two polymorphs and a solvatomorph of a new dimethylammonium polytungstate-decakis(dimethylammonium) dihydrogendodecatungstate, (Me₂NH₂)₁₀(W₁₂O₄₂)·nH₂O (n = 10 or 11)-have been synthesized. Their structures were characterized by single-crystal X-ray diffraction and solid-phase NMR methods. The shape of the dodecatungstate anions is essentially the same in all three structures, their interaction with the cations and water of crystallization, however, is remarkably variable, because the latter forms different hydrogen-bonded networks, and provides a highly versatile matrix. Accordingly, the N-H⋯O and C-H⋯O hydrogen bonds are positioned in each crystal lattice in a variety of environments, characteristic to the structure, which can be distinguished by solid-state ¹H-CRAMPS, ¹³C, ¹⁵N CP MAS and ¹H-¹³C heteronuclear correlation NMR. Thermogravimetry of the solvatomorphs also reflect the difference and multiformity of the environment of the water molecules in the different crystal lattices. The major factors behind the variability of the matrix are the ability of ammonium cations to form two hydrogen bonds and the rigidity of the polyoxometalate anion cage. The positions of the oxygen atoms in the latter are favourable for the formation of bifurcated and trifurcated cation-anion hydrogen bonds, some which are so durable that they persist after the crystals are dissolved in water, forming ion associates even in dilute solutions. The H atom involved in furcated hydrogen bonds cannot be exchanged by deuterium when the compound is dissolved in D₂O. An obvious consequence of the versatility of the matrix is the propensity of these compounds to form multiple polymorphs.

Polyoxometalate-based composite materials in electrochemistry: state-of-the-art progress and future outlook

Polyoxometalates (POMs) have been developed as a class of promising smart material candidates not only due to their multitudinous architectures but also their good redox activities and outstanding electron and proton transport capacities. Recently, abundant studies on POMs composited with metal nanoparticles (NPs), carbon materials (e.g., carbon nanotubes (CNTs), carbon quantum dots (CQDs), graphene), and conducting polymers or highly-porous framework materials (e.g., MOFs, ZIFs) have been performed and POM-based composite materials (PCMs) undoubtedly show enhanced stability and improved electrochemical performances. Therefore, POMs and PCMs are of increasing interest in electrocatalysis, electrochemical detection and energy-related fields (such as fuel cells, redox flow batteries and so on), thus, developing novel PCMs has long been the key research topic in POM chemistry. This review mainly summarizes some representative advances in PCMs with electrochemical applications in the past ten years, expecting to provide some useful guidance for future research.

First series of mixed (PIII, SeIV)-heteroatomoriented rare-earth-embedded polyoxotungstates containing distinct building blocks

A series of unprecedented mixed heteroatoms-oriented rare-earth-embedded heteropolyoxotungstates 1–8 were prepared and the 1@CMWCNT-GCE electrochemical sensing performances toward DA and UA were studied.

An organic chromophore -modified samarium-containing polyoxometalate: excitation-dependent color tunable behavior from the organic chromophores to the lanthanide ion

An organic–inorganic hybrid Ln-POM display reversible color-tunable photoluminescence properties based on excitation from 260 nm to 350 nm, emitting color from blue to pink.

Modified polyoxometalate: a novel monocapped bi-supporting and reduced α-Keggin structure {PMo12O40[Cu(2,2'-bpy)]}[Cu(2,2'-bpy)(en)(H2O)]2

A novel modified polyoxometalate, {PMo₁₂O₄₀[Cu(2,2'-bpy)]}[Cu(2,2'-bpy)(en)(H₂O)]₂ [2,2'-bpy is 2,2'-bipyridyl (C₁₀H₈N₂) and en is ethylenediamine (C₂H₈N₂)], has been synthesized hydrothermally and structurally characterized by elemental analysis, TG, IR, XPS and single-crystal X-ray diffraction. The structural analysis reveals that the compound contains the reduced Keggin polyanion [PMo₁₂O₄₀]^6- as the parent unit, which is monocapped by [Cu(2,2'-bpy)]²⁺ fragments via four bridging O atoms on an {Mo₄O₄} pit and bi-supported by two [Cu(2,2'-bpy)(en)(H₂O)]²⁺ coordination cations simultaneously. There exist strong intramolecular π-π stacking between the capping and supporting units, which play a stabilizing role during the crystallization of the compound. Adjacent POM clusters are further aggregated to form a three-dimensional supramolecular network through noncovalent forces, hydrogen bonding and π-π stacking interactions. In addition, the photocatalytic properties were investigated in detail, and the results indicated that the compound can be used as a photocatalyst towards the decomposition of the organic pollutant methylene blue (MB).

Synthesis, characterization, and photoluminescence properties of three two-dimensional lanthanide-containing Dawson-type polyoxometalates

Three isostructural lanthanide-containing polyoxometalates with 2D network architectures were successfully obtained under hydrothermal conditions.