Polyoxometalates (POMs) are molecular metal‐oxide anions applied in energy conversion and storage, manipulation of biomolecules, catalysis, as well as materials design and assembly. Although often overlooked, the interplay of intrinsically anionic POMs with organic and inorganic cations is crucial to control POM self‐assembly, stabilization, solubility, and function. Beyond simple alkali metals and ammonium, chemically diverse cations including dendrimers, polyvalent metals, metal complexes, amphiphiles, and alkaloids allow tailoring properties for known applications, and those yet to be discovered. This review provides an overview of fundamental POM–cation interactions in solution, the resulting solid‐state compounds, and behavior and properties that emerge from these POM–cation interactions. We will explore how application‐inspired research has exploited cation‐controlled design to discover new POM materials, which in turn has led to the quest for fundamental understanding of POM–cation interactions.

Corrosion of stone by acid rain and deterioration from biofilms are global problems for industrial and residential buildings as well as cultural heritage, such as statues or historic buildings. Herein we show how typical building stones can be protected from corrosion ("weathering") and biofilm formation ("biodeterioration") by application of thin films of polyoxometalate-based ionic liquids (POM-ILs). Stone samples are coated with hydrophobic, acid resistant POM-ILs featuring biocidal properties. Exposure of the samples to simulated acid rain showed negligible corrosion compared to the significant deterioration of unprotected samples; in addition the biocidal properties of the POM-ILs suppress the formation of biofilms on coated stone slabs. A new class of modular molecular materials for protecting stones can now be developed for use in construction, environmental protection, and cultural heritage preservation.

Filtration is an established water-purification technology.H owever,d ue to lowf low rates,t he filtration of large volumes of water is often not practical. Herein, we report an alternative purification approach in whichamagnetic nanoparticle composite is used to remove organic, inorganic, microbial, and microplastics pollutants from water.T he composite is based on ap olyoxometalate ionic liquid (POM-IL) adsorbed onto magnetic microporous core-shell Fe 2 O 3 / SiO 2 particles,g iving am agnetic POM-supported ionic liquid phase (magPOM-SILP). Efficient, often quantitative removal of several typical surface water pollutants is reported together with facile removal of the particles using apermanent magnet. Tuning of the composite components could lead to new materials for centralized and decentralized water purification systems.

Core-shell materials are promising functional materials for fundamental research and industrial application, as their properties can be adapted for specific applications. In particular, particles featuring iron or iron oxide as core material are relevant since they combine magnetic and catalytic properties. The addition of an SiO2 shell around the core particles introduces additional design aspects, such as a pore structure and surface functionalization. Herein, we describe the synthesis and application of iron-based core-shell nanoparticles for two different fields of research that is heterogeneous catalysis and water purification. The iron-based core shell materials were characterized by transmission electron microscopy, as well as N2-physisorption, X-ray diffraction, and vibrating-sample magnetometer measurements in order to correlate their properties with the performance in the target applications. Investigations of these materials in CO2 hydrogenation and water purification show their versatility and applicability in different fields of research and application, after suitable individual functionalization of the core-shell precursor. For design and application of magnetically separable particles, the SiO2 shell is surface-functionalized with an ionic liquid in order to bind water pollutants selectively. The core requires no functionalization, as it provides suitable magnetic properties in the as-made state. For catalytic application in synthesis gas reactions, the SiO2-stabilized core nanoparticles are reductively functionalized to provide the catalytically active metallic iron sites. Therefore, Fe@SiO2 core-shell nanostructures are shown to provide platform materials for various fields of application, after a specific functionalization.

Enhancement of photochemical water oxidation using a graphene oxide matrix for [Na17[Mn6P3W24O94(H2O)2]·43H2O@GO] soft-oxometalate is shown.