Stereogenic‐Only‐at‐Metal Asymmetric Catalysts

Chirality is an essential feature of asymmetric catalysts. This review summarizes asymmetric catalysts that derive their chirality exclusively from stereogenic metal centers. Reported chiral‐at‐metal catalysts can be divided into two classes, namely, inert metal complexes, in which the metal fulfills a purely structural role, so catalysis is mediated entirely through the ligand sphere, and reactive metal complexes. The latter are particularly appealing because structural simplicity (only achiral ligands) is combined with the prospect of particularly effective asymmetric induction (direct contact of the substrate with the chiral metal center). Challenges and solutions for the design of such reactive stereogenic‐only‐at‐metal asymmetric catalysts are discussed.     

Rare‐Earth‐Metal Methylidene Complexes

Transition‐metal carbene complexes have been known for about 50 years and widely applied as reagents and catalysts in organic transformations. In contrast, the carbene chemistry of the rare‐earth metals is much less developed, but has attracted the research interest in the recent years. In this field rare‐earth‐metal alkylidene, especially methylidene, compounds are an emerging class of compounds with a high synthetic potential for organometallic chemistry and maybe in the future also for organic chemistry.     

Transition‐Metal π‐Ligation of a Tetrahalodiborane

The reaction of tetraiododiborane (B₂I₄) with trans‐[Pt(BI₂)I(PCy₃)₂] gives rise to the diplatinum(II) complex [{(Cy₃P)(I₂B)Pt}₂(μ₂:η³:η³‐B₂I₄)], which is supported by a bridging diboranyl dianion ligand [B₂I₄]^2?. This complex is the first transition‐metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B₂X₄ (X=halide) unit of any type to a metal center.     

Rare‐Earth‐Metal Dialkynyl Dimethyl Aluminates

A new class of rare‐earth‐metal alkynyl complexes has been prepared. The reactions of the tris(tetramethylaluminate)s of lanthanum, praseodymium, samarium, yttrium, holmium, and thulium, [Ln(AlMe₄)₃], with phenylacetylene afforded compounds [Ln{(μ‐C?CPh)₂AlMe₂}₃] (Ln=La ( 1 ), Pr ( 2 ), Sm ( 3 ), Y ( 4 ), Ho ( 5 ), Tm ( 6 )). All of these compounds have been characterized by NMR spectroscopy, X‐ray crystallography, and by elemental analysis. NMR spectroscopic studies of the series of para‐ magnetic compounds [Ln(AlMe₄)₃] and [Ln{(μ‐C?CPh)₂AlMe₂}₃] have also been performed.     

Water‐in‐Supercritical CO2 Microemulsion Stabilized by a Metal Complex

Herein we propose for the first time the utilization of a metal complex for forming water‐in‐supercritical CO₂ (scCO₂) microemulsions. The water solubility in the metal‐complex‐stabilized microemulsion is significantly improved compared with the conventional water‐in‐scCO₂ microemulsions stabilized by hydrocarbons. Such a microemulsion provides a promising route for the in situ CO₂ reduction catalyzed by a metal complex at the water/scCO₂ interface.     

Revisiting the Electroplating Process for Lithium‐Metal Anodes for Lithium‐Metal Batteries

Electroplating has been studied for centuries, not only in the laboratory but also in industry for machinery, electronics, automobile, aviation, and other fields. The lithium‐metal anode is the Holy Grail electrode because of its high energy density. But the recyclability of lithium‐metal batteries remains quite challenging. The essence of both conventional electroplating and lithium plating is the same, reduction of metal cations. Thus, industrial electroplating knowledge can be applied to revisit the electroplating process for lithium‐metal anodes. In conventional electroplating, some strategies like using additives, modifying substrates, applying pulse current, and agitating electrolyte have been explored to suppress dendrite growth. These methods are also effective in lithium‐metal anodes. Inspired by that, we revisit the fundamental electroplating theory for lithium‐metal anodes in this Minireview, mainly drawing attention to the theory of electroplating thermodynamics and kinetics. Analysis of essential differences between traditional electroplating and plating/stripping of lithium‐metal anodes is also presented. Thus, industrial electroplating knowledge can be applied to the electroplating process of lithium‐metal anodes to improve commercial lithium‐metal batteries and the study of lithium plating/stripping can further enrich the classical electroplating technique.     

Amine‐Templated One‐Dimensional Metal Sulfates Including a Mixed‐Valent Fe Compound with a Half‐Kagome Structure

Organically templated metal sulfates are relatively new. Six amine‐templated transition‐metal sulfates with different types of chain structures, including a novel iron sulfate with a chain structure corresponding to one half of the kagome structure, were synthesized by hydro/solvothermal methods. Amongst the one‐dimensional metal sulfates, [C₁₀N₂H₁₀][Zn(SO₄)Cl₂] ( 1 ) is the simplest, being formed by corner‐linked ZnO₂Cl₂ and SO₄ tetrahedra. [C₆N₂H₁₈][Mn(SO₄)₂(H₂O)₂] ( 2 ) and [C₂N₂H₁₀][Ni(SO₄)₂(H₂O)₂] ( 3 ) have ladder structures comprising four‐membered rings formed by SO₄ tetrahedra and metal–oxygen octahedra, just as in the mineral kröhnkite. [C₄N₂H₁₂][V^III(OH)(SO₄)₂]?H₂O ( 4 ) and [C₄N₂H₁₂][VF₃(SO₄)] ( 5 ) exhibit chain topologies of the minerals tancoite and butlerite, respectively. The structure of [C₄N₂H₁₂][H₃O][Fe^IIIFe^II F₆(SO₄)] ( 6 ) is noteworthy in that it corresponds to half of the hexagonal kagome structure. It exhibits ferrimagnetic properties at low temperatures and the absence of frustration, unlike the mixed‐valent iron sulfate with the full kagome structure.     

Transition‐Metal Nitride Core@Noble‐Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

Core–shell architectures offer an effective way to tune and enhance the properties of noble‐metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X‐ray photoelectron spectroscopy revealed significant core‐level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d‐states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. The ability to control shell coverage and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.     

Blending Non‐Group‐3 Transition Metal and Rare‐Earth Metal into a C80 Fullerene Cage with D5h Symmetry

Rare‐earth metals have been mostly entrapped into fullerene cages to form endohedral clusterfullerenes, whereas non‐Group‐3 transition metals that can form clusterfullerenes are limited to titanium (Ti) and vanadium (V), and both are exclusively entrapped within an I_h‐C₈₀ cage. Non‐Group‐3 transition‐metal‐containing endohedral fullerenes based on a C₈₀ cage with D_5h symmetry, V_xSc_3?xN@D_5h‐C₈₀ (x=1, 2), have now been synthesized, which exhibit two variable cluster compositions. The molecular structure of VSc₂N@D_5h‐C₈₀ was unambiguously determined by X‐ray crystallography. According to a comparative study with the reported Ti‐ and V‐containing clusterfullerenes based on a I_h‐C₈₀ cage and the analogous D_5h‐C₈₀‐based metal nitride clusterfullerenes containing rare‐earth metals only, the decisive role of the non‐Group‐3 transition metal on the formation of the corresponding D_5h‐C₈₀‐based clusterfullerenes is unraveled.     

Silica‐Coated Metal Nanoparticles

The advanced high‐quality synthesis of dense and porous silica‐coated nanostructures is enjoying ever‐increasing research interests for their important properties and diverse applications, especially for catalytic, controlled release, colorimetric diagnostics, photothermal therapy, surface enhanced Raman scattering (SERS) detection, and so forth. In this timely Focus Review, we summarize the up‐to‐date synthesis strategies, improved properties, and emerging applications of silica‐coated metal nanoparticles. In particular, the large scale synthesis of silica‐coated metal nanoparticles and the recent development of hollowed‐out silica‐coated metal nanoparticles by silica dissolution are emphasized for new and practical applications.     

Thin‐Film Metal Hydrides

The goal of the medieval alchemist, the chemical transformation of common metals into nobel metals, will forever be a dream. However, key characteristics of metals, such as their electronic band structure and, consequently, their electric, magnetic and optical properties, can be tailored by controlled hydrogen doping. Due to their morphology and well‐defined geometry with flat, coplanar surfaces/interfaces, novel phenomena may be observed in thin films. Prominent examples are the eye‐catching hydrogen switchable mirror effect, the visualization of solid‐state diffusion and the formation of complex surface morphologies. Thin films do not suffer as much from embrittlement and/or decrepitation as bulk materials, allowing the study of cyclic absorption and desorption. Therefore, thin‐metal hydride films are used as model systems to study metal–insulator transitions, for high throughput combinatorial research or they may be used as indicator layers to study hydrogen diffusion. They can be found in technological applications as hydrogen sensors, in electrochromic and thermochromic devices. In this review, we discuss the effect of hydrogen loading of thin niobium and yttrium films as archetypical examples of a transition metal and a rare earth metal, respectively. Our focus thereby lies on the hydrogen induced changes of the electronic structure and the morphology of the thin films, their optical properties, the visualization and the control of hydrogen diffusion and on the study of surface phenomena and catalysis.     

Titania‐Coated Metal Nanostructures

The synergistic effect between metal and TiO₂ nanoparticles brings about new, enhanced functionalities for a myriad of applications, ranging from labeling and sensing to catalysis and surface‐enhanced Raman scattering. Although extensive work has been done in the preparation of concentric TiO₂‐coated metal nanostructures, current methods for the synthesis of noncentrosymmetric morphologies are still very limited. This Focus review summarizes the various methods used to prepare TiO₂‐coated metal nanostructures, with a particular emphasis on noncentrosymmetric morphologies, their novel plasmonic properties, and their promising applications in the fields of catalysis and photocatalysis.     

Rare‐Earth‐Metal Nitridophosphates through High‐Pressure Metathesis

Developing a synthetic method to target an broad spectrum of unknown phases can lead to fascinating discoveries. The preparation of the first rare‐earth‐metal nitridophosphate LiNdP₄N₈ is reported. High‐pressure solid‐state metathesis between LiPN₂ and NdF₃ was employed to yield a highly crystalline product. The in situ formed LiF is believed to act both as the thermodynamic driving force and as a flux to aiding single‐crystal formation in dimensions suitable for crystal structure analysis. Magnetic properties stemming from Nd³⁺ ions were measured by SQUID magnetometry. LiNdP₄N₈ serves as a model system for the exploration of rare‐earth‐metal nitridophosphates that may even be expanded to transition metals. High‐pressure metathesis enables the systematic study of these uncharted regions of nitride‐based materials with unprecedented properties.     

Two‐Dimensional Noble‐Metal Chalcogenides and Phosphochalcogenides

Noble‐metal chalcogenides, dichalcogenides, and phosphochalcogenides are an emerging class of two‐dimensional materials. Quantum confinement (number of layers) and defect engineering enables their properties to be tuned over a broad range, including metal‐to‐semiconductor transitions, magnetic ordering, and topological surface states. They possess various polytypes, often of similar formation energy, which can be accessed by selective synthesis approaches. They excel in mechanical, optical, and chemical sensing applications, and feature long‐term air and moisture stability. In this Minireview, we summarize the recent progress in the field of noble‐metal chalcogenides and phosphochalcogenides and highlight the structural complexity and its impact on applications.