Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

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Surprising Impact of Donor Charge on the Water Exchange Rates of Gd(III) AAZTA Derivatives

Coordinated water molecules in Bis-hydrated Gd(III)-AAZTA derivatives have unexpectedly fast exchange rates, which do not follow the trend with complex charge observed previously for contrast agents used in magnetic resonance imaging (MRI).


Abstract

We report the synthesis of three new heptadentate ligands derived from H4AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid) that contain a dimethyl-amide group (AAZTA-MA)3−, two dimethyl-amide groups (AAZTA-BMA)2− or two acetylglycine groups (AAZTA(Gly)2)4−. The corresponding Gd(III) complexes were investigated using 1H NMR relaxometry and 17O NMR chemical shifts and transverse relaxation rates. A computational DFT study was also performed to aid the analysis of the NMR data. The Gd(III) complexes contain two water molecules coordinated to the metal ion. In contrast to the prevailing trend, the amide derivatives discussed in this context exhibit comparatively rapid water exchange rates that do not align with the changes in the overall electric charge of the complexes: k ex 298=14.4×106 s−1, 14.5×106 s−1 and 9.56×106 s−1 for [Gd(AAZTA-MA)(H2O)2], [Gd(AAZTA-BMA)(H2O)2]+ and [Gd(AAZTA(Gly)2(H2O)2]−, respectively. The analysis of the data and the computational work suggest that the relatively fast water exchange rates could be linked to the occurrence of associatively activated mechanisms, which is somewhat unexpected for nine-coordinated complexes.

Citric acid as multidentate flexible ligand for multinuclear late‐3 d‐metal complexes and single‐molecule magnets

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Citric acid as multidentate flexible ligand for multinuclear late-3 d-metal complexes and single-molecule magnets

Citrate which is a unique bio-derived ligand has great potential to serve as a bridge between spin quantum magnetism and green chemistry. This review focuses on the structures and magnetism of discrete citrate complexes of late-3d-metals, as well as their single-molecule magnet properties.


Abstract

Citric acid (citH4) is a ubiquitous product in nature with an interesting chemistry owing to its three carboxy and one hydroxy groups, which can be deprotonated in a stepwise manner into six kinds of citrate anions involving two protonation isomers. Deprotonated citrates easily coordinate to late-3d-metal ions (Mn, Fe, Co, Ni, Cu, and Zn), affording complexes including mono-, di-, tri-, tetra-, hexa-, hepta-, octa-, nona-, and 21-nuclear complexes with a variety of structures. Magnetic interactions between metal centers are mainly generated via superexchange through hydroxylate or carboxylate bridging, whereas weaker magnetic dipole interactions appear in the absence of superexchange interactions. In citrate complexes, both ferromagnetic and antiferromagnetic interactions have been found. Citrate has a great potential to serve as a bridge between spin quantum magnetism and green chemistry. In this review, the structures and magnetism of discrete citrate complexes of late-3d-metals, as well as their single-molecule magnet properties are discussed.

Synthesis of Bifunctional Catalysts for the Cycloaddition of CO2 to Epoxides through an Epoxide‐driven Strategy

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Synthesis of Bifunctional Catalysts for the Cycloaddition of CO2 to Epoxides through an Epoxide-driven Strategy

Bifunctional homogeneous and recyclable heterogeneous single-component catalysts for the cycloaddition of CO2 to epoxides were obtained through a simple method based on the ring-opening of opportunely functionalized epoxides and applied for the synthesis of cyclic carbonates under atmospheric CO2 pressure.


Abstract

The design of molecular scaffolds bearing multiple functional groups for the activation and ring-opening of epoxides is a crucial challenge for the synthesis of efficient homogeneous and heterogeneous catalysts that are used for the cycloaddition reaction of CO2 to epoxides. Traditional approaches to prepare such multifunctional catalysts often imply multistep synthetic procedures and expensive building blocks. In this work we show that bifunctional catalysts for the cycloaddition of CO2 to epoxides bearing a Lewis acid metal and a quaternary ammonium halide group can be prepared in just two steps starting from an opportunely designed epoxide precursor by using inexpensive substrates. Such a readily accessible catalyst was applied for the cycloaddition of CO2 to a series of epoxides under atmospheric conditions generally leading to quantitative substrate conversion and high carbonate selectivities. Importantly, we also show that the epoxide-driven concept developed for the preparation of the molecular catalyst, could be applied to prepare recyclable heterogeneous systems for the target cycloaddition reaction.

Fibrous Material Structure Developments for Sustainable Heterogeneous Catalysis – An Overview

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Fibrous Material Structure Developments for Sustainable Heterogeneous Catalysis – An Overview

The main types of fibrous structures for catalyst (applications) are addressed, all the way from the nanoscale to the macroscale and back by combining different morphologies into advanced materials for today's environmental challenges. These materials show a very large potential but future research is needed to further expand the use of fibrous structures in industrial processes.


Abstract

The continuous development of advanced catalysts to increase process yield and selectivity is crucial. A high specific surface area and a good active phase dispersion are generally essential to create catalytic materials with a large number of active sites. Notably, materials with a fibrous morphology are appealing because of their large surface-to-volume ratio and flexibility. This contribution highlights the morphology of different types of fibrous structures currently under investigation, all the way from the nanoscale to the macroscale and back, where the distinction lies in the length and diameter of the fibers, as well as in the connection between the structures. Fibers with at least one submicron to nanoscale characteristic result in a higher yield, but can display practical usability issues when unbound. Therefore, fibrous structure catalysts with a balance between the small diameter and handleability are important for industrial viability. By combining different morphologies, the best of both nanomaterials and macroscopic integer materials can be combined into advanced catalytic materials. This overview showcases the large potential of these materials but makes clear that further research is needed to keep expanding the use and effectiveness of fibrous structures in catalysis.

Ultrathin 2D Porphyrin‐Based Zr‐MOF Nanosheets as Heterogeneous Catalysts for Styrene Epoxidation and Benzylic C‐H Oxidation

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Selective oxidation of hydrocarbons using molecular oxygen as sole oxidant under mild conditions remains a challenging task. In this context, metal-organic frameworks (MOFs) have been widely used in various oxidation reactions due to their porosity, high surface area and designability. However, the slow diffusion of substrates/products in micropores of three-dimensional (3D) bulk MOFs hinders the efficient catalytic performance of such materials. Herein an ultrathin two-dimensional (2D) porphyrin-based Zr-MOF nanosheet (Zr-TCPP) is synthesized through modulator-control strategy. Subsequently, various metal ions are anchored into the porphyrin ring by post synthesis modification to afford a series of 2D Zr-TCPP(M) (M=Mn, Fe, Co, Ni, Cu and Zn). Various structural characterization techniques indicate Zr-TCPP(M) is nanoflower structure with ultrathin nanoplate petals which provides fully exposed accessible active sites. Among them, Zr-TCPP(Fe) shows excellent catalytic performance in styrene epoxidation reactions and benzylic C-H oxidation reactions using O2 as sole oxidant under ambient temperature and pressure. The remarkable activity arises from high density of exposed porphyrin-Fe active sites, low diffusion barriers for substrates and products, as well as a similar homogeneous reaction space. Furthermore, Zr-TCPP(Fe) nanosheet is easily recycled by centrifugation and reused at least five times without significant loss of catalytic activity.

High‐Throughput Exploration of a Thioxanthone‐catalyzed Photoredox C−O Coupling

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High-Throughput Exploration of a Thioxanthone-catalyzed Photoredox C−O Coupling

A metallaphotoredox C−O coupling reaction was optimized through the use of High Throughput Experimentation (HTE) and Design of Experiment (DoE) techniques. The resulting methodology utilizes more sustainable and cost effective materials than previously reported conditions, and has been demonstrated on a range of substrates from 300 μL up to 500 mL scales.


Abstract

Using High-Throughput Experimentation (HTE), a visible light-mediated etherification method was developed, employing the organic photocatalyst thioxanthen-9-one (TXO) and a commercially available, air-stable nickel source. Design of Experiments (DoE) techniques were utilized in conjunction with HTE to identify optimal reaction conditions which are mild, cost-effective, robust and therefore suitable for use in an industrial setting. A diverse substrate scope was prepared via parallel synthesis and selected examples were demonstrated on a 4.2 mmol scale in batch. Furthermore, the reaction was successfully performed on an 83 mmol scale, utilizing a standard jacketed reactor and Kessil PR160 L lamps.

Preparation of TiO2/Ni‐NG Mesoporous Microspheres and Photocatalytic Hydrogen Evolution Properties

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Preparation of TiO2/Ni-NG Mesoporous Microspheres and Photocatalytic Hydrogen Evolution Properties

Forming TiO2 mesoporous microspheres with small particle size and can provide abundant active sites for photocatalytic hydrogen production due to their high surface area and mesoporous structure. In addition, graphene is selected as a co-catalyst for photocatalytic hydrogen production due to the excellent conductivity and high specific surface area of graphene materials, which has excellent enrichment effect on photogenerated electrons of the photocatalyst and can effectively inhibit the recombination of photogenerated carriers and improve the photocatalytic hydrogen production activity.


Abstract

The regulation of surface active sites and structures is a key factor affecting the performance of photocatalysts. In order to prepare monodisperse anatase TiO2 mesoporous microspheres with higher specific surface area, smaller pore size and particle size, a dual-surfactant orientation assembly method was selected. Graphene (NG) was selected as a cocatalyst to compound with mesoporous TiO2 and nickel doping was performed on the cocatalyst to improve the photocatalytic hydrogen production activity of the semiconductor photocatalyst. Through proper regulation and rational design, the semiconductor photocatalyst with desired properties was prepared. SEM characterization of mesoporous titanium dioxide (TiO2/Ni-NG) with graphene cocatalyst proved that TiO2 nanospheres have good monodispersion, and TiO2 nanospheres are well supported on graphene cocatalyst. The composite material belonged to mesoporous group with the pore size being mainly distributed between 10–20 nm. The loading of graphene and Ni-NG cocatalyst increased the absorption band edge by 9 nm and 38 nm, respectively, and the band gap decreased by 0.07 eV and 0.16 eV, respectively. The selection of graphene as cocatalyst improved the hydrogen production activity of photocatalyst and nickel doping was very effective in the modification of graphene. For reaction time of 2.5 h, the H2 production of TiO2/Ni-NG material reached 1.767 mmol/g which was 7.27 times that of TiO2/NG composite material.

Probing the effects of gold doping on structural, electronic and nonlinear optical properties of caged X20H20 (X=Si, Ge, Sn, Pb) clusters

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Probing the effects of gold doping on structural, electronic and nonlinear optical properties of caged X20H20 (X=Si, Ge, Sn, Pb) clusters

Using first-principles methods, we explored the doping of gold atom into carbon family clusters (Si20, Ge20, Sn20, Pb20), and the Au atom and charged states can effectively modulate the electronic properties of clusters, while the neutral Au@X20H20 (X=Si, Sn) clusters possess the large nonlinear optical responses, especially for Au@Sn20H20, served as novel optoelectronic materials.


Abstract

Carbon family elements (Si, Ge, Sn, Pb) have attracted a lot of attention because of their unique structural features and potential applications in microelectronics industry. Here, the structure, chemical stability, electronic properties, and nonlinear optical properties of neutral and charged Au@X20H20 (X=Si, Ge, Sn, Pb) clusters have been systematically studied using density-functional theory calculations. Structurally, the neutral/anionic Au@X20H20 (X=Si, Ge, Sn) as well as cationic Au@Pb20H20 possess Au-endohedral (XH)20 unit, forming fullerene-like framework, whereas other species are Au-doped structures with hydrogen-bridged bond. Analysis of binding energy and HOMO-LUMO energy gaps reveals that the charged clusters possess high chemical stabilities due to closed-shell structures. The charge transfers from X20 cage to Au atom, and the Au atom acts as electron acceptor. The Au atom and charged states play an important role in the structural stability, and can effectively modulate the electronic properties of clusters. Interestingly, the neutral Au@X20H20 (X=Si, Sn) clusters possess large first hyperpolarizabilities, especially for Au@Sn20H20, which has remarkably giant value (~5.65×108 a. u.), and the enhanced NLO behaviors can be further explained by the TDDFT calculation. The work may provide a theoretical reference for further applications considered as novel cluster-assembled nanomaterials.

Recent Advancement in Quantum Dot Modified Layered Double Hydroxide towards Photocatalytic, Electrocatalytic, and Photoelectrochemical Applications

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Recent Advancement in Quantum Dot Modified Layered Double Hydroxide towards Photocatalytic, Electrocatalytic, and Photoelectrochemical Applications

This review thoroughly analyses the fabrication process, structural, morphological characterization, different applications which highlights the role of QDs (carbon dots, sulfide QDs, and oxide QDs) within the QD/LDH heterostructure, serving as interlayer support-catalyst, mediator, semiconductor and sensitizer. These integrated heterostructures demonstrate superior performance in photocatalytic (PC) electrocatalytic (EC) and photoelectrochemical (PEC) water splitting, with enhanced long–term stability.


Abstract

Layered double hydroxides (LDHs) is a category of 2D materials that possess excellent physicochemical properties for enhancing photocatalytic (PC), electrocatalytic (EC), and photoelectrochemical (PEC) performances. However, pristine LDH encounters challenges like sluggish charge–carrier mobility, high rate of electron–hole recombination, low conductivity, and tendency to agglomerate, making them unsuitable for practical applications. Therefore, modifications such as composite preparations, co-catalyst integration, semiconductor coupling, and ternary heterostructure engineering have been explored to disclose new possibilities for LDHs in PC, EC, and PEC applications. In the realm of semiconducting materials aimed at enhancing LDH productivity, quantum dots (QDs) i. e., 0D materials have proven to be effective due to their advantages, including abundant reserves, affordability, and environmental friendliness. This review explores the role of QDs as interlayer support, co-catalyst, mediator, semiconductor, and sensitizer in QDs@LDH heterostructures to achieve superior photocatalytic activities. These QD-infused heterostructures also deliver improved EC and PEC water–splitting performance coupled with long–term stabilities. Additionally, this review delves into characterization techniques, intrinsic structural features, and designing of the QD@LDH heterostructures. Future scopes and challenges in constructing and cutting–edge theoretical anticipations of QD@LDH are also discussed. This review may be a guiding light to a sustainable approach to outperform QD-modified LDH for versatile catalysts.

Mechanistic Insights into Ru‐catalyzed Alkene Epoxidation with Nitrous Oxide as a Terminal Oxidant

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Mechanistic Insights into Ru-catalyzed Alkene Epoxidation with Nitrous Oxide as a Terminal Oxidant

Simple kinetic studies provided insights to inform future catalyst designs able to employ N2O as an oxidant under mild conditions. Results suggest the use of low alkene concentrations, possible saturation behavior at high N2O pressures and a potential catalyst turnover involving disproportionation of RuIV(O) and RuIV(O)(N2O).


Abstract

Nitrous oxide (N2O) is a greenhouse gas produced in the manufacture of 6,6-nylon and nitric acid. While an attractive oxidant that releases only N2 as a by-product, the kinetic stability of N2O typically requires high temperatures and pressures for activation. This work describes initial kinetics of oxygen transfer in the epoxidation of cholesteryl acetate with N2O catalysed by D4 -Ru(VI)(por)(O)2 complexes in efforts to provide a better mechanistic understanding of this chemistry. Insights include a need for low concentrations of the alkene to avoid competitive binding to the metal, possible saturation behavior at high N2O pressures, transfer of only one oxygen of RuVI(O)2 to substrate and a possible catalyst turnover involving disproportionation of RuIV(O) and RuIV(O)(N2O) to active RuVI(O)2, RuIV(O) and N2. These insights will be used in future designs of improved catalysts and reaction protocols that may operate efficiently at low pressures of N2O and ambident temperature.