Catalytic epoxidation activity of keplerate polyoxomolybdate nanoball toward aqueous suspension of olefins under mild aerobic conditions

Exploration and Insights on Topology Adjustment of Giant Heterometallic Cages Featuring Inorganic Skeletons Assisted by Machine Learning

Inorganic molecular cages are emerging multifunctional molecular-based platforms with the unique merits of rigid skeletons and inherited properties from constituent metal ions. However, the sensitive coordination bonds and vast synthetic space have limited their systematic exploration. Herein, two giant cage-like clusters featuring the organic ligand-directed inorganic skeletons of Ni4[La74Ni104(IDA)96(OH)184(C2O4)12(H2O)76]·(NO3)38·(H2O)120 (La74Ni104, 5 × 5 × 3 - C2O4) and [La84Ni132(IDA)108(OH)168(C2O4)24(NO3)12(H2O)116]·(NO3)72·(H2O)296 (La84Ni132, 5 × 5 × 5 - C2O4) were discovered by a high-throughput synthetic search. With the assistance of machine learning analysis of the experimental data, phase diagrams of the two clusters in a four-parameter synthetic space were depicted. The effect of alkali, oxalate, and other parameters on the formation of clusters and the mechanism regulating the size of two n × m × l clusters were elucidated. This work uses high-throughput synthesis and machine learning methods to improve the efficiency of 3d-4f cluster discovery and finds the highest-nuclearity 3d-4f cluster to date by regulating the size of the n × m × l inorganic cages through oxalate ions, which pushes the synthetic methodology study on elusive inorganic giant cages in a significantly systematic way.

Tetrahedral Keggin Core Tunes the Visible Light-Assisted Catalase-Like Activity of Icosahedral Keplerate Shell

In this work, the effect of Keggin polyoxometalates encapsulated in Keplerate {Mo₇₂Fe₃₀} shell (K shell) on the visible light-assisted catalase-like activity (H₂O₂ dismutation) of the resulting core-shell clusters PMo₁₂@K, SiMo₁₂@K, and BW₁₂@K was investigated. Superior photodismutation activity of PMo₁₂@K compared to that of K shell and two other core-shell clusters was discovered. The homogeneity of PMo₁₂@K and its improved oxidative stability, increased redox potential, and reduced band gap caused by a synergistic effect between the Keplerate shell and Keggin core seem reasonable to explain such a superiority. The light-dependent photocatalytic performance of PMo₁₂@K evaluated by action spectra revealed a maximum apparent quantum efficiency (AQY) at 400 nm, demonstrating the visible light-driven photocatalytic reaction. A first-order rate constant of 2 × 10^-4 s^-1 and activation energy of 108.8 kJ mol^-1 alongside a turnover frequency of 0.036 s^-1 and a total turnover number of up to ∼3800 approved the effective photocatalytic activity and improved the oxidative stability of PMo₁₂@K. A nonradical photocatalytic mechanism through a Fe-OOH intermediate was proposed. Thus, the structure, optical activity, and oxidative stability of a host Keplerate-type nanocluster can be tuned significantly by encapsulation of a guest, like "cluster-in-cluster" structures, which opens the scope for introducing new visible light-sensitive hierarchical nanostructures.

Highly Reactive Heterogeneous Nanofibers Catalyst Based on [Mo154] Clusters for Green Aerobic Oxidation of Sulfur Mustard Analogues under Ambient Conditions

BACKGROUND

Due to the increasing chemical and biological threats posed by terrorist attacks, there is a need to design and prepare nanofibers (NFs) with the ability to neutralize CWAs. For this purpose polyacrylonitrile NFs and polyoxomolybdate [Mo154] (abbreviated as PAN NFs/[Mo154]) as a heterogeneous catalyst was prepared by electrospinning method with a diameter of about 100nm.

OBJECTIVE

The PAN NFs/[Mo154] catalyze the selective aerobic oxidation of sulfur mustard stimulants, such as 2-chloroethyl ethyl sulfide (2-CEES) and 2-chloroethyl phenyl sulfide (2-CEPS) under green and "ambient" conditions (25◦C, 1atm O2) in presence of ethanol with high efficiency and selectivity. 2-CEES was selected as a model reaction to optimize the parameters of the reaction.

METHOD

The progress of the reaction was evaluated after different times using GC-FID, GC-MS and TLC. The reaction product was also confirmed by 1H-NMR spectroscopy.

RESULT

The aerobic oxidation results of 2-CEES showed that PAN NFs/[Mo154] have a conversion of 98% to produce only a nontoxic product, 2-CEESO with selectivity of 100% after 45min. The results were performed using [Mo154] without any PAN NFs for comparison. Whereas [Mo154] converts only 52% of 2-CEES under the identical conditions.

CONCLUSION

Heterogeneous PAN NFs/[Mo154] catalyst was reused after washing with solvent up to 5 steps without leaching of [Mo154] from PAN NFs and without any loss in efficiency due to the morphology of NFs. In addition to the recovery of PAN NFs/[Mo154] in different cycles, the use of FT-IR, UV-Vis and TEM techniques confirms the stability and morphology of PAN NFs/[Mo154] after the fifth cycle, 2-CEES oxidation. According to our information, this report is the first use of PAN NFs enriched with [Mo154] for aerobic oxidation of sulfur mustard simulants.

The precise modification of nanoscaled Keplerate-type polyoxometalate with NH2-groups: reactive sites, mechanisms and dye conjugation

The interaction of alkoxysilanes with nanoscaled giant polyoxoclusters is a challenging route for efficiently building blocks for supramolecular smart-tune design. 3-aminopropyltrimethoxysilane (APTMS) treatment grafts amino groups onto the surface of...

An efficient and recyclable Cu@UiO-67-BPY catalyst for the selective oxidation of alcohols and the epoxidation of olefins

A novel CuCl2-UiO-67-BPY catalyst was synthesized for catalytic oxidation with up to 99% yield and 99% selectivity.

Metal-metal bonds in polyoxometalate chemistry

Half a century ago, F. Albert Cotton emphasized the relevance of metal-metal bonding in the constitution of cluster materials. Based on his description, nanoscale polyoxometalates (POMs) normally would not be regarded as cluster materials. One reason is that metal-metal bonding is typically associated with inorganic systems featuring metal centres in low oxidation states, a feature that is not common for POMs. However, over the past decades, there have been increasing reports on POMs integrating different types of metal-metal bonding. This article conceptualises and reviews the area of metal-metal bonded POMs, and their preparation and physicochemical properties. Attention is given to the changes in the electronic structure of POMs, the emergence of covalent dynamics and its impact on the development of applications in catalysis, nanoswitches, donor-acceptor systems, electron storage materials and nanoelectronics (i.e., "POMtronics").

Solvent-driven crystal-crystal transformation and morphology change in a 2D layered inorganic POM-based framework

In this paper, a pure 2D inorganic POM-based framework underwent a single crystal to single crystal conversion when soaked in organic solvents that are miscible with water, forming a more densely packed identical framework accompanying the formation of nanowires. The change in morphology is closely related to the surface tension of water, and the lower surface tension achieved by dehydration promotes the formation of nanowires, which is revealed by SXRD, PXRD, SEM, TGA and electrochemical impedance spectroscopy (EIS).

Chromium-catalysed efficient N-formylation of amines with a recyclable polyoxometalate-supported green catalyst

A simple and efficient protocol for the formylation of amines with formic acid, catalyzed by a polyoxometalate-based chromium catalyst, is described. Notably, this method shows excellent activity and chemoselectivity for the formylation of primary amines; diamines have also been successfully employed. Importantly, the chromium catalyst is potentially non-toxic, environmentally benign and safer than the widely used high valence chromium catalysts such as CrO₃ and K₂Cr₂O₇. The catalyst can be recycled several times with a negligible impact on activity. Finally, a plausible mechanism is provided based on the observation of intermediate and control experiments.

A Cooperative Effect in a Novel Bimetallic Mo-V Nanocomplex Catalyzed Selective Aerobic C-H Oxidation

In this study, a new heterobimetallic Mo(VI)-V(V) organosilicon Schiff base complex has been prepared and characterized by different techniques, such as FTIR, Raman, MS, ICP-AES, TGA, and XPS. The bimetallic nanocomplex, revealed by TEM images, showed high oxidation stability and desired activity in the aerobic oxidation of a structurally diverse set of benzylic alcohols in ethanol as a safe solvent. Further, oxidation of benzylic hydrocarbons successfully occurred, producing the target compounds in high yields and excellent selectivities. Our results demonstrated a cooperative effect between Mo(VI) and V(V) as redox active sites in an organosilicon Schiff base framework. A facile and practical reusability of the solid catalyst at the end of the reaction was observed.

Recent Progress in Application of Molybdenum-Based Catalysts for Epoxidation of Alkenes

Epoxides are important industrial intermediates applied in a variety of industrial processes. During the production of epoxides, catalysts have played an irreplaceable and unique role. In this review, the historic progress of molybdenum-based catalysts in alkene epoxidation are covered and an outlook on future challenge discussed. Efficient catalysts are demonstrated including soluble molybdenum complexes, polyoxometalates catalysts, molybdenum-containing metal organic frameworks, silica supported molybdenum-based catalysts, polymer supported molybdenum-based catalysts, magnetic molybdenum-based catalysts, hierarchical molybdenum-based catalysts, graphene-based molybdenum containing catalysts, photocatalyzed epoxidation catalysts, and some other systems. The effects of different solvents and oxidants are discussed and the mechanisms of epoxidation are summarized. The challenges and perspectives to further enhance the catalytic performances in alkenes epoxidation are presented.

A nanoscopic icosahedral {Mo72Fe30} cluster catalyzes the aerobic synthesis of benzimidazoles

In this study, the catalytic efficiency of amorphous {Mo₇₂Fe₃₀} nanocapsules as a safe Keplerate polyoxometalate in organic synthesis was exploited. The easy-made solid catalyst exhibited high efficiency using a very low dosage (0.02–0.05 mol%) in the catalyzed condensation of various aromatic 1,2-diamines and aldehydes for the aerobic synthesis of benzimidazoles with very small E-factor values (0.11–0.33). The superior catalytic activity of amorphous nanoclusters compared to that of its crystalline counterpart was demonstrated. The high activity and recyclability of heterogeneous catalysts in a green reaction media under oxygen atmosphere, make this environmentally benign organic process appropriate for our applied goals.

Catalytic activity of amorphous {Mo₇₂Fe₃₀} nanoclusters as a safe Keplerate polyoxometalate in aerobic synthesis of benzimidazoles was described.

Nickel(ii) riboflavin complex as an efficient nanobiocatalyst for heterogeneous and sustainable oxidation of benzylic alcohols and sulfides

A novel Ni(ii)Rf₂ nanocomplex was prepared, which efficiently oxidizes a wide range of benzyl alcohols and sulfides by employing ideal oxidants in green reaction media.

Evolutionary Metal Oxide Clusters for Novel Applications: Toward High-Density Data Storage in Nonvolatile Memories

Because of current fabrication limitations, miniaturizing nonvolatile memory devices for managing the explosive increase in big data is challenging. Molecular memories constitute a promising candidate for next-generation memories because their properties can be readily modulated through chemical synthesis. Moreover, these memories can be fabricated through mild solution processing, which can be easily scaled up. Among the various materials, polyoxometalate (POM) molecules have attracted considerable attention for use as novel data-storage nodes for nonvolatile memories. Here, an overview of recent advances in the development of POMs for nonvolatile memories is presented. The general background knowledge of the structure and property diversity of POMs is also summarized. Finally, the challenges and perspectives in the application of POMs in memories are discussed.

Visible-light driven catalase-like activity of blackberry-shaped {Mo72Fe30} nanovesicles: combined kinetic and mechanistic studies

Catalase-like activity of blackberry-shaped {Mo₇₂Fe₃₀} nanovesicles was exploited in aqueous solution under visible-light irradiation.

Green catalysis for the selective oxidation of sulfides with high turnover numbers in water at room temperature

A hybrid catalyst based on monoprotonated divanadium-substituted phosphotungstate ([γ-HPV₂W₁₀O₄₀]⁴⁻) was synthesized and used for the selective oxidation of sulfides.

Deep oxidative desulfurization of dibenzothiophene with {Mo132} nanoballs supported on activated carbon as an efficient catalyst at room temperature

{Mo₁₃₂}/AC could be used as an efficient catalyst for deep oxidative removal of refractory sulfur compounds in fossil fuels.

Coding the Assembly of Polyoxotungstates with a Programmable Reaction System

Chemical transformations are normally conducted in batch or flow mode, thereby allowing the chemistry to be temporally or spatially controlled, but these approaches are not normally combined dynamically. However, the investigation of the underlying chemistry masked by the self-assembly processes that often occur in one-pot reactions and exploitation of the potential of complex chemical systems requires control in both time and space. Additionally, maintaining the intermediate constituents of a self-assembled system "off equilibrium" and utilizing them dynamically at specific time intervals provide access to building blocks that cannot coexist under one-pot conditions and ultimately to the formation of new clusters. Herein, we implement the concept of a programmable networked reaction system, allowing us to connect discrete "one-pot" reactions that produce the building block{W11O38} ≡ {W11} under different conditions and control, in real time, the assembly of a series of polyoxometalate clusters {W12O42} ≡ {W12}, {W22O74} ≡ {W22} 1a, {W34O116} ≡ {W34} 2a, and {W36O120} ≡ {W36} 3a, using pH and ultraviolet-visible monitoring. The programmable networked reaction system reveals that is possible to assemble a range of different clusters using {W11}-based building blocks, demonstrating the relationship between the clusters within the family of iso-polyoxotungstates, with the final structural motif being entirely dependent on the building block libraries generated in each separate reaction space within the network. In total, this approach led to the isolation of five distinct inorganic clusters using a "fixed" set of reagents and using a fully automated sequence code, rather than five entirely different reaction protocols. As such, this approach allows us to discover, record, and implement complex one-pot reaction syntheses in a more general way, increasing the yield and reproducibility and potentially giving access to nonspecialists.

Electronic Structure Studies on the Whole Keplerate Family: Predicting New Members

A comprehensive study of the electronic structure of nanoscale molecular oxide capsules of the type [{M^VI (M^VI )₅ O₂₁ }₁₂ {M'^V₂ O₂ (μ-X)(μ-Y)(L^n- )}₃₀ ]^(12+n)- is presented, where M,M'=Mo,W, and the bridging ligands X,Y=O,S, carried out by means of density functional theory. Discussion of the electronic structure of these derivatives is focused on the thermodynamic stability of each of the structures, the one having the highest HOMO-LUMO gap being M=W, M'=Mo, X=Y=S. For the most well-known structure M=M'=Mo, X=Y=O, [Mo₁₃₂ O₃₇₂ ]^12- , the chemical bonding of several ligands to the {Mo^V₂ O₂ (μ-O)₂ } linker moiety produces negligible effects on its stability, which is evidence of a strong ionic component in these bonds. The existence of a hitherto unknown species, namely W₁₃₂ with both bridging alternatives, is discussed and put into context.

Anions coordinating anions: analysis of the interaction between anionic Keplerate nanocapsules and their anionic ligands

Keplerates are a family of anionic metal oxide spherical capsules containing up to 132 metal atoms and some hundreds of oxygen atoms. These capsules holding a high negative charge of -12 coordinate both mono-anionic and di-anionic ligands thus increasing their charge up to -42, even up to -72, which is compensated by the corresponding counter-cations in the X-ray structures. We present an analysis of the relative importance of several energy terms of the coordinate bond between the capsule and ligands like carbonate, sulphate, sulphite, phosphinate, selenate, and a variety of carboxylates, of which the overriding component is contributed by solvation/de-solvation effects.