Prediction of Solution Behavior via Calorimetric Measurements Allows for Detailed Elucidation of Polyoxometalate Transformation

The solution behavior of a polyoxometalate cluster, LiNa-U₂₄Pp₁₂ (Li₂₄Na₂₄[(UO₂O₂)₂₄(P₂O₇)₁₂]) that consists of 24 uranyl ions, peroxide groups, and 12 pyrophosphate linkers, was successfully predicted based on new thermodynamic results using a calorimetric method recently described for uranyl peroxide nanoclusters (UPCs), molybdenum blues, and molybdenum browns. The breakdown of LiNa-U₂₄Pp₁₂ and formation of U₂₄ (Li₂₄[UO₂O₂OH]₂₄) was monitored in situ via Raman spectroscopy using a custom heating apparatus. A combination of analytical techniques confirmed the simultaneous existence of U₂₄Pp₁₂ and U₂₄ midway through the conversion process and U₂₄ as the single end product. The application of a molecular weight filter resulted in a complete and successful separation of UPCs from solution and, in conjunction with DOSY results, confirmed the presence of large intermediate cluster building blocks.

Hybrid polyoxometalates as post-functionalization platforms: from fundamentals to emerging applications

Polyoxometalates (POMs) represent an important group of metal-oxo nanoclusters, typically comprised of early transition metals in high oxidation states (mainly V, Mo and W). Many plenary POMs exhibit good pH, solvent, thermal and redox stability, which makes them attractive components for the design of covalently integrated hybrid organic-inorganic molecules, herein referred to as hybrid-POMs. Until now, thousands of organic hybrid-POMs have been reported; however, only a small fraction can be further functionalized using other organic molecules or metal cations. This emerging class of 'post-functionalizable' hybrid-POMs constitute a valuable modular platform that permits coupling of POM properties with different organic and metal cation functionalities, thereby expanding the key physicochemical properties that are relevant for application in (photo)catalysis, bioinorganic chemistry and materials science. The post-functionalizable hybrid-POM platforms offer an opportunity to covalently link multi-electron redox responsive POM cores with virtually any (bio)organic molecule or metal cation, generating a wide range of materials with tailored properties. Over the past few years, these materials have been showcased in the preparation of framework materials, functional surfaces, surfactants, homogeneous and heterogeneous catalysts and light harvesting materials, among others. This review article provides an overview on the state of the art in POM post-functionalization and highlights the key design and structural features that permit the discovery of new hybrid-POM platforms. In doing so, we aim to make the subject more comprehensible, both for chemists and for scientists with different materials science backgrounds interested in the applications of hybrid (POM) materials. The review article goes beyond the realms of polyoxometalate chemistry and encompasses emerging research domains such as reticular materials, surfactants, surface functionalization, light harvesting materials, non-linear optics, charge storing materials, and homogeneous acid-base catalysis among others.

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.

Main-chain polyoxometalate-containing donor–acceptor conjugated copolymers: synthesis, characterization, morphological studies and applications in single-component photovoltaic cells

Single-component solar cells of main-chain polyoxometalate-containing donor–acceptor conjugated copolymers show efficiencies comparable to those conjugated polymers with covalently bonded fullerenes.

Structure- and solvent-triggered influences in the self-assembly of polyoxometalate–steroid conjugates

The supramolecular structures formed by polyoxometalate–steroid conjugates can be greatly influenced by molecular structures and solution components.