Benchmarking Uranyl Peroxide Capsule Chemistry in Organic Media

Abstract

Uranyl peroxide capsules are a recent addition to polyoxometalate (POM) chemistry. Ten years of development has ensued only in water, while transition metal POMs are commonly exploited in aqueous and organic media, controlled by counterions or ligation to render the clusters hydrophilic or hydrophobic. Here, new uranyl POM behavior is recognized in organic media, including (1) stabilization and immobilization of encapsulated hydrophilic countercations, identified by Li nuclear magnetic resonance (NMR) spectroscopy, (2) formation of new cluster species upon phase transfer, (3) extraction of uranyl clusters from different starting materials including simulated spent nuclear fuel, (4) selective phase transfer of one cluster type from a mixture, and (5) phase transfer of clusters from both acidic and alkaline media. The capsule morphology of the uranyl POMs renders accurate characterization by X‐ray scattering, including the distinction of geometrically similar clusters. Compositional analysis of the aqueous phase post‐extraction provided a quantitative determination of the ion exchange process that enables transfer of the clusters into the organic phase. Preferential partitioning of uranyl POMs into organic media presents new frontiers in metal ion behavior and chemical reactions in the confined space of the cluster capsules in hydrophobic media, as well as the reactivity of clusters at the organic/aqueous interface.

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

“…Instead, we will discuss what is known about the structures of both ordered (crystalline) and non‐ordered cluster‐surfactant phases derived from POM‐counter‐cation aggregation (see Figure ), and how this can lead to tailoring these hybrid materials for applications such as ion conductivity or energy storage. The structure of SECs has been inferred by SAXS in solution, as well as X‐ray reflectivity, TEM and molecular modeling of Langmuir layers . For surface‐deposited Langmuir layers, cluster‐surfactant phases, single‐crystal cluster‐surfactant phases, and SECs in solution, we can generally conclude that the size of the POM controls the resulting organization of POMs and surfactants in the solid‐phase.…”

“…The SECs with their bulky shell of long-chain hydrocarbons can be dissolved in organic solvents and these can be transferred to a surface for molecular devices with electrochemical or electrochromic response, catalytic function, [123,126] gas adsorption, [123] or Li + [127] or H + [128] conduction for energy conversion and storage. Organically-soluble SECs have also been proposed for applications including stabilization of emulsions, [129] extraction and separation of uranium [130] and NMR paramagnetic relaxation reagents. [131] In the spirit of this comprehensive Review about POMcounter-cations, we will not go in depth into SEC applications, as this has been recently reviewed.…”

Jenseits von Ladungsausgleich: Gegenkationen in der Polyoxometallat‐Chemie

“…Stattdessen werden wir beschreiben, was an Strukturinformation über geordnete (kristalline) sowie nichtgeordnete Cluster‐Tensid‐Aggregate auf Basis von POM‐Kation‐Systemen bekannt ist (Abbildung ), und wie dieses Wissen genutzt werden kann, um Hybridmaterialien für Anwendungen in der Protonenleitung oder Energiespeicherung zu entwickeln. Die Struktur von SECs in Lösung wurde aus SAXS‐Messungen sowie Röntgenreflexion, TEM und molekularer Modellierung von Langmuir‐Schichten abgeleitet . Für Langmuir‐Schichten auf Oberflächen, Cluster‐Tensid‐Phasen, einkristalline Cluster‐Tensid‐Phasen und SECs in Lösung kann festgestellt werden, dass die Größe des POMs die sich ergebende Struktur von POM und Tensid in der festen Phase kontrolliert.…”

Inhomogeneous Distribution of Cationic Surfactants around Anionic Molecular Clusters

“…Attaching organic chains onto the surface of such clusters leads to the formation of amphiphilic hybrid molecules with new or enhanced functions, and available for fabricating various supramolecular structures and functional materials. Using the interaction between oppositely charged surfactant molecules with macroions to make surfactant‐encapsulated clusters (SECs) with an hydrophobic surface is another approach, which can transfer the macroions from polar solvents to organic media, and further fabricate into functional thin films, highly ordered porous materials, or be used for synthesizing ionic liquid crystals, and so on.…”