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There is considerable interest in multivalent cation batteries, such as those based on magnesium, calcium or aluminium. Most attention has focused on magnesium. In all cases the metal anode represents a significant challenge. Recent work has shown that calcium can be plated and stripped, but only at elevated temperatures, 75 to 100 °C, with small capacities, typically 0.165 mAh cm-2 , and accompanied by significant side reactions. Here we demonstrate that calcium can be plated and stripped at room temperature with capacities of 1 mAh cm-2 at a rate of 1 mA cm-2 , with low polarization (∼100 mV) and in excess of 50 cycles. The dominant product is calcium, accompanied by a small amount of CaH2 that forms by reaction between the deposited calcium and the electrolyte, Ca(BH4 )2 in tetrahydrofuran (THF). This occurs in preference to the reactions which take place in most electrolyte solutions forming CaCO3 , Ca(OH)2 and calcium alkoxides, and normally terminate the electrochemistry. The CaH2 protects the calcium metal at open circuit. Although this work does not solve all the problems of calcium as an anode in calcium-ion batteries, it does demonstrate that significant quantities of calcium can be plated and stripped at room temperature with low polarization.

The Soai reaction has profoundly impacted chemists’ perspective of autocatalysis, chiral symmetry breaking, absolute asymmetric synthesis and its role in the origin of biological homochirality. Here we describe the unprecedented observation of asymmetry-amplifying autocatalysis in the alkylation of 5-(trimethylsilylethynyl)pyridine-3-carbaldehyde using diisopropylzinc. Kinetic studies with a surrogate substrate and spectroscopic analysis of a series of zinc alkoxides that incorporate specific structural mutations reveal a ‘pyridine-assisted cube escape’. The new tetrameric cluster functions as a catalyst that activates the substrate through a two-point binding mode and poises a coordinated diisopropylzinc moiety for alkyl group transfer. Transition-state models leading to both the homochiral and heterochiral products were validated by density functional theory calculations. Moreover, experimental and computational analysis of the heterochiral complex provides a definitive explanation for the nonlinear behaviour of this system. Our deconstruction of the Soai system reveals the structural logic for autocatalyst evolution, function and substrate compatibility—a central mechanistic aspect of this iconic transformation.The discovery of amplifying autocatalysis in a pyridine-3-carbaldehyde system facilitates a mechanistic deconstruction of the Soai reaction. A tetrameric autocatalyst, assembled by a combination of steric effects and nitrogen–zinc coordination, activates the substrate by two-point binding. This is followed by intra-complex isopropyl group transfer that generates the product alkoxide with high homochiral fidelity.

The high efficiency of widely applied Noyori-type hydrogenation catalysts arises from the N–H moiety coordinated to a metal centre, which stabilizes rate-determining transition states through hydrogen-bonding interactions. It was proposed that a higher efficiency could be achieved by substituting an N–M′ group (M′ = alkali metals) for the N–H moiety using a large excess of metal alkoxides (M′OR); however, such a metal-hydride amidate intermediate has not yet been isolated. Here we present the synthesis, isolation and reactivity of a metal-hydride amidate complex (HMn–NLi). Kinetic studies show that the rate of hydride transfer from HMn–NLi to a ketone is 24-fold higher than that of the corresponding amino metal-hydride complex (HMn–NH). Moreover, the hydrogenation of N -alkyl-substituted aldimines was realized using HMn–NLi as the active catalyst, whereas HMn–NH is much less effective. These results highlight the superiority of M/NM′ bifunctional catalysis over the classic M/NH bifunctional catalysis for hydrogenation reactions. Noyori-type hydrogenation catalysts consist of an N–H moiety coordinated to a metal centre. Now, a metal-hydride amidate complex (HMn–NLi) has been isolated and found to have superior reactivity and catalytic performance compared with the corresponding HMn–NH complex, highlighting the superiority of M/NM′ bifunctional catalysis over the classic M/NH bifunctional catalysis for hydrogenation reactions.

The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, sol-gel chemistry gathers plenty of fascinating strategies to prepare materials from solution state precursors. Low temperature chemistry, reproducibility, and high surface to volume ratios of obtained products are features that add merit to this technology. The development of different and fascinating procedure was fostered by the availability of new molecular precursors, chelating agents and templates, with the great advantage of tailoring the physico-chemical properties of the materials through the manipulation of the synthesis conditions. The aim of this review is to present an overview of the “traditional” sol-gel synthesis of tailored and multifunctional inorganic materials and their application in the main domain of heterogeneous catalysis. One of the main achievements is to stress the versatility of sol-gel preparation by highlighting its advantage over other preparation methods through some specific examples of the synthesis of catalysts.

The term cluster has been proposed in Inorganic Chemistry for species featuring well-defined metal-metal bond based structures and implies inherent stability against metal core transformation. The present article provides additional arguments for the formation of metal oxo-alkoxide species on the action of external self-assembly forces, without invoking such stability. These species are easily restructured on hydrolysis in aqueous medium and their alleged photo and electro catalytic reactivity may actually be due to metal oxide nanoparticles resulting from their transformation. A new term “paperbag compound” is proposed instead of ‘cluster’ to denote oligonuclear non-cluster species. New insights into the reactivity of metal oxide nanoparticles in biological systems can be obtained from analysis of structure and bonding parameters in paperbag compounds as molecular models. Graphical Abstract Highlights Self-assembly phenomena have been analyzed for oxo-alkoxide and polyoxometalate (POM) species. Trends in preservation and transformation of metal-oxide cores have been illustrated by new and literature-based single crystal data. Reactivity of metal oxo-alkoxides in water leading to their transformation into metal oxide nanoparticles has been traced using literature data. A new term, “paperbag compound” has been proposed for metal oxo-alkoxides and POMs as an alternative to misleading term cluster.

In this paper, fine, homogeneous, and high purity MgAl 2 O 4 nanopowder was synthesized by a novel facile non-hydrolytic sol-gel (NHSG) route. The spinel powders were characterized by various techniques, such as DTA-TG, XRD, SEM, and TEM. It is found that the formation of pure single-phase spinel MgAl 2 O 4 powder begins at 500 °C due to the obtaining of Mg-O-Al bonds in the gel. No impurity appears at the whole temperature range (from 450 to 750 °C), which is ascribed to the exact stoichiometry of magnesium and aluminium in the bimetallic alkoxides Mg(Al(OEt) 3 ) 2 to form MgAl 2 O 4 . The average particle size of MgAl 2 O 4 synthesized at 700 °C is about 6.96 nm with high dispersion and crystallinity. NHSG synthesis method from bimetallic alkoxides is expected to be a promising preparation method for the synthesis of compound oxides. Schematic diagram of novel facile nonhydrolytic sol-gel in-situ synthesis for MgAl2O4 synthesis. There proceeded an in situ reaction of Mg powders, Al powders and anhydrous ethanol under the catalysis of iodine to form the MgAl2(EtO)8 bimetallic alkoxides. The formed bimetallic alkoxides reacted with each other by way of EtOEt elimination polycondensation. Thus, a polynuclear agnesium aluminum oxo-alkoxide containing heterometal atoms and without auxiliary ligands appeared. After calcination, the crystalline MgAl2O4 nanoparticles were through the rearrangement of Mg-O-Al network. Highlights A novel nonhydrolytic sol-gel route for MgAl2O4 synthesis is developed. Precursors of bimetallic alkoxides effectively avoid the impurities. The synthesis mechanism is confirmed.

SignificanceDirect air capture (DAC) of CO2 is essential for carbon net negative technologies. The sorbent properties of amines, alkoxides, and phenoxides are computationally screened for their suitability for DAC. The alkoxides and phenoxides are found to be more suitable for aqueous DAC than amines because of their greater water tolerance and capture stoichiometry of 1:1, in contrast to 2:1 for amines. Higher CO2 binding constants broadly correlate with higher pKa, which can lead to an undesirable acid–base reaction with water. Structural properties that lead to greater CO2 binding at milder pKas were identified and experimentally validated. This study identifies promising sorbent candidates for aqueous DAC, as well as presents a computational workflow to optimize other classes of functional molecules. Aqueous direct air capture (DAC) is a key technology toward a carbon negative infrastructure. Developing sorbent molecules with water and oxygen tolerance and high CO2 binding capacity is therefore highly desired. We analyze the CO2 absorption chemistries on amines, alkoxides, and phenoxides with density functional theory calculations, and perform inverse molecular design of the optimal sorbent. The alkoxides and phenoxides are found to be more suitable for aqueous DAC than amines thanks to their water tolerance (lower pKa prevents protonation by water) and capture stoichiometry of 1:1 (2:1 for amines). All three molecular systems are found to generally obey the same linear scaling relationship (LSR) between pKCO2 and pKa, since both CO2 and proton are bonded to the nucleophilic (alkoxy or amine) binding site through a majorly σ bonding orbital. Several high-performance alkoxides are proposed from the computational screening. Phenoxides have comparatively poorer correlation between pKCO2 and pKa, showing promise for optimization. We apply a genetic algorithm to search the chemical space of substituted phenoxides for the optimal sorbent. Several promising off-LSR candidates are discovered. The most promising one features bulky ortho substituents forcing the CO2 adduct into a perpendicular configuration with respect to the aromatic ring. In this configuration, the phenoxide binds CO2 and a proton using different molecular orbitals, thereby decoupling the pKCO2 and pKa. The pKCO2–pKa trend and off-LSR behaviors are then confirmed by experiments, validating the inverse molecular design framework. This work not only extensively studies the chemistry of the aqueous DAC, but also presents a transferrable computational workflow for understanding and optimization of other functional molecules.

This review presents a brief overview of recent insights into general reaction pathways in sol-gel synthesis of metal oxides. Metal-based sol-gel precursors display kinetically unhindered reactivity, combining high reaction speed with reversibility on a molecular level. The process producing metal oxide sols can thus be described as nucleation of an oxide phase with growth option efficiently precluded by extremely low solubility. The emerging nuclei are essentially Polyoxometalate (POM) species, with sizes in the colloid range starting from about 2 nm. They are stabilized in solution by colloid forces (charge interactions, hydrogen bonding, van der Waals forces), defined by the nature and arrangement of species on their surface, which permits them to be denoted as Micelles Templated by Self-Assembly of Ligands (MTSALs). The sol-gel transition occurs on aggregation of particles resulting in percolation. Exploiting this mechanism, it is possible to produce materials with controlled porosity, biocompatibility, and even to access thermodynamically challenging phases that cannot be produced by conventional synthetic techniques. Graphical Abstract Metal oxide Sol-Gel can be described as nucleation of an oxide phase resulting from one-step coordination equilibrium in solution, followed by aggregation without growth. Highlights Metal alkoxides are strong Brönsted and Lewis bases, undergoing hydrolysis via proton-assisted S N 1 mechanism Hydrolysis and polycondensation are for metal alkoxides a single kinetic phenomenon, leading to nucleation of an oxide phase The metal oxide nuclei are colloid particles 2–5 nm in size with Polyoxometalate structure—a well-ordered core in a shell of ligands, permitting to describe them as Micelles Templated by Self-Assembly of ligands

Since the discovery of its photocatalytic properties, titanium dioxide has remained one of the most popular and widely used metal oxide photocatalysts. Its major drawback, however, lies in the narrow region (UV) of sunlight necessary to produce reactive oxygen species. This have been countered by sensitizing with organic dyes to red-shift the absorption spectrum but also with doping of other metals and non-metals. Volume doping or surface modification have demonstrated improved photocatalytic efficiency, mainly via red-shifted absorption by introduction of intermediate energy states between the valence band (VB) and conduction band (CB) and increased number of surface hydroxyl groups (which can form reactive hydroxyl radicals) from charge compensation, and in some cases by improved surface-adsorption of organic molecules. Doped titania and complex titanates have traditionally been produced via, for instance, co-precipitation of mixed metal salts or via solid-state synthesis. While these methods usually are simple, they offer limited control over size, shape, and phase composition. An alternative is the use of single-source precursors (SSPs), i.e., molecules already containing the desired metal ratio in a homogenous distribution. The last one or two decades have seen an increased number of reported transition metal-doped titanium oxo-alkoxides (TOA), particularly for the first-row transition metals as potential single-source precursors (SSP) for doped titania and complex titanates. This review aims at providing an overview of TM-doped TOAs, focusing on first and second row TM elements, with special emphasis on their synthesis, photochemical properties, and their applications as SSPs. Graphical abstract Highlights The synthesis and structures of transition metal-doped titanium oxo-alkoxy complexes are reviewed. Their applications as precursors for complex oxide materials are reported with focus on photo(electrochemical) applications. An extensive set of references is provided.

Electrochemical processes for CO 2 mitigation can be broadly categorized into two approaches: CO 2 capture via electrochemically generated bases and CO 2 conversion through electrochemical reduction. Recent advancements have been concentrated to developing methods that efficiently capture and release CO 2 or reduce base-CO 2 adducts while regenerating bases for subsequent CO 2 capture. In this study, we introduce an electrochemical strategy that integrates CO 2 capture and conversion through a series of domino reactions initiated by the electrochemical generation of organic bases. This method involves the electrochemical deprotonation of halohydrin molecules, which generate hydrogen and halo-alkoxides that capture CO 2 and spontaneously undergo intramolecular cyclization to yield cyclic carbonates. Direct and indirect Faradaic efficiency of up to 100% is achieved for both hydrogen and ethylene carbonate production, demonstrating highly selective sequential capture and conversion reactions. Our system provides a scalable pathway for synthesizing various cyclic carbonates directly from diluted CO 2 sources. Electrochemical CO 2 mitigation involves two main approaches: capture and release, or direct conversion. Here, the authors report a method that integrates both by converting CO 2 into ethylene carbonate using electrochemically activated substrates.