Finding new ways of using visible light (or, more specifically, solar irradiation) to drive commercially significant and/or challenging chemical processes is an ongoing research goal. ...Polyoxometalates (POMs) are discrete, metal-oxide clusters which are cheap, robust and easily synthesised but can also act as versatile molecular building blocks, allowing for astonishing variety in their structures and properties. In particular, the rich redox chemistry and inherent photo-activity of POMs makes them attractive for use in a variety of photochemical applications, however POMs characteristically only absorb strongly in the UV region. In this perspective, we discuss the various strategies which have been employed in order to sensitise POMs to visible light, with a particular focus on hybrid inorganic-organic POM species. We will discuss the two clear photo-activation mechanisms which have been developed to date and provide an outlook on some of the possible future directions of the field.
Approaches to the visible light photo-sensitisation of organic-inorganic hybrid polyoxometalates are presented and future trends discussed.
This Tutorial Review describes how the development of dissolved redox-active molecules is beginning to unlock the potential of three of the most promising 'next-generation' battery technologies - ...lithium-air, lithium-sulfur and redox-flow batteries. Redox-active molecules act as mediators in lithium-air and lithium-sulfur batteries, shuttling charge between electrodes and substrate systems and improving cell performance. In contrast, they act as the charge-storing components in flow batteries. However, in each case the performance of the molecular species is strongly linked to their solubility, electrochemical and chemical stability, and redox potentials. Herein we describe key examples of the use of redox-active molecules in each of these battery technologies and discuss the challenges and opportunities presented by the development and use of redox-active molecules in these applications. We conclude by issuing a "call to arms" to our colleagues within the wider chemical community, whose synthetic, computational, and analytical skills can potentially make invaluable contributions to the development of next-generation batteries and help to unlock of world of potential energy-storage applications.
In this Tutorial Review, we describe the critical role redox active molecular species are playing in the development of the next generation of "beyond-lithium ion" battery technologies.
This review provides a comprehensive overview of recent advances in the supramolecular organisation and hierarchical self-assembly of organo-functionalised hybrid polyoxometalates (hereafter referred ...to as hybrid POMs), and their emerging role as multi-functional building blocks in the construction of new nanomaterials. Polyoxometalates have long been studied as a fascinating outgrowth of traditional metal-oxide chemistry, where the unusual position they occupy between individual metal oxoanions and solid-state bulk oxides imbues them with a range of attractive properties (
e.g.
solubility, high structural modularity and tuneable properties/reactivity). Specifically, the capacity for POMs to be covalently coupled to an effectively limitless range of organic moieties has opened exciting new avenues in their rational design, while the combination of distinct organic and inorganic components facilitates the formation of complex molecular architectures and the emergence of new, unique functionalities. Here, we present a detailed discussion of the design opportunities afforded by hybrid POMs, where fine control over their size, topology and their covalent and non-covalent interactions with a range of other species and/or substrates makes them ideal building blocks in the assembly of a broad range of supramolecular hybrid nanomaterials. We review both direct self-assembly approaches (encompassing both solution and solid-state approaches) and the non-covalent interactions of hybrid POMs with a range of suitable substrates (including cavitands, carbon nanotubes and biological systems), while giving key consideration to the underlying driving forces in each case. Ultimately, this review aims to demonstrate the enormous potential that the rational assembly of hybrid POM clusters shows for the development of next-generation nanomaterials with applications in areas as diverse as catalysis, energy-storage and molecular biology, while providing our perspective on where the next major developments in the field may emerge.
Organic-inorganic hybrid polyoxometalates are versatile building blocks for the self-assembly of functional supramolecular materials.
We report the time‐resolved supramolecular assembly of a series of nanoscale polyoxometalate clusters (from the same one‐pot reaction) of the form: H(10+m)Ag18Cl(Te3W38O134)2n, where n=1 and m=0 for ...compound 1 (after 4 days), n=2 and m=3 for compound 2 (after 10 days), and n=∞ and m=5 for compound 3 (after 14 days). The reaction is based upon the self‐organization of two {Te3W38} units around a single chloride template and the formation of a {Ag12} cluster, giving a {Ag12}‐in‐{W76} cluster‐in‐cluster in compound 1, which further aggregates to cluster compounds 2 and 3 by supramolecular Ag‐POM interactions. The proposed mechanism for the formation of the clusters has been studied by ESI‐MS. Further, control experiments demonstrate the crucial role that TeO32−, Cl−, and Ag+ play in the self‐assembly of compounds 1–3.
Cluster‐in‐cluster: Polyoxometalate clusters H(10+m)Ag18Cl(Te3W38O134)2n with n=1 and m=0, n=2 and m=3, and n=∞ and m=5 were isolated after 4, 10, and 14 days from the same reaction mixture. The proposed mechanism for the formation of the clusters was confirmed by ESI‐MS studies and control experiments, which demonstrate the crucial role that TeO32−, Cl−, and Ag+ play in the self‐assembly of these compounds.
Climate change and variability influence temperature and rainfall, which impact vector abundance and the dynamics of vector-borne disease transmission. Climate change is projected to increase the ...frequency and intensity of extreme climate events. Mosquito-borne diseases, such as dengue fever, are primarily transmitted by Aedes aegypti mosquitoes. Freshwater availability and temperature affect dengue vector populations via a variety of biological processes and thus influence the ability of mosquitoes to effectively transmit disease. However, the effect of droughts, floods, heat waves, and cold waves is not well understood. Using vector, climate, and dengue disease data collected between 2013 and 2019 in Kenya, this retrospective cohort study aims to elucidate the impact of extreme rainfall and temperature on mosquito abundance and the risk of arboviral infections. To define extreme periods of rainfall and land surface temperature (LST), we calculated monthly anomalies as deviations from long-term means (1983–2019 for rainfall, 2000–2019 for LST) across four study locations in Kenya. We classified extreme climate events as the upper and lower 10% of these calculated LST or rainfall deviations. Monthly Ae. aegypti abundance was recorded in Kenya using four trapping methods. Blood samples were also collected from children with febrile illness presenting to four field sites and tested for dengue virus using an IgG enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). We found that mosquito eggs and adults were significantly more abundant one month following an abnormally wet month. The relationship between mosquito abundance and dengue risk follows a non-linear association. Our findings suggest that early warnings and targeted interventions during periods of abnormal rainfall and temperature, especially flooding, can potentially contribute to reductions in risk of viral transmission
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Access to asymmetrically functionalized polyoxometalates is a grand challenge as it could lead to new molecular nanomaterials with multiple or modular functionality. Now, a simple one‐pot synthetic ...approach to the isolation of an asymmetrically functionalized organic–inorganic hybrid Wells–Dawson polyoxometalate in good yield is presented. The cluster bears two organophosphonate moieties with contrasting physical properties: a chelating metal‐binding group, and a long aliphatic chain that facilitates solvent‐dependent self‐assembly into soft nanostructures. The orthogonal properties of the modular system are effectively demonstrated by controlled assembly of POM‐based redox‐active nanoparticles. This simple, high‐yielding synthetic method is a promising new approach to the preparation of multi‐functional hybrid metal oxide clusters, supermolecular systems, and soft‐nanomaterials.
A one‐pot approach to the isolation of an asymmetrically functionalized organic–inorganic hybrid Wells–Dawson polyoxometalate is presented. The cluster bears two organophosphonate moieties with contrasting physical properties: a chelating metal‐binding group and a long aliphatic chain unit that facilitates solvent‐dependent self‐assembly into soft redox‐active nanostructures.
Despite the vast number of polyoxometalate clusters now known, an ongoing and important challenge is to understand causality in the assembly of “complex” clusters at a mechanistic level, since this ...is the only way the rational, targeted synthesis of new compounds will ever be achieved. Often, the complexity of the reactions themselves makes such investigations near impossible, as very small changes can often make dramatic differences. Herein, we explore a very simple A + B binary synthetic system that gives rise to the facile assembly of two isomeric anions, FeIII(H2O)2{γ-FeIIISiW9O34(H2O)}211– (1) and FeIII(H2O)2{γ-FeIII 2SiW8O33(H2O)2}{γ-SiW10O35}11– (2), which can be formed as individual and dimeric species (3) and (4). Furthermore, the simple binary nature of this synthetic system allowed its investigation by a comprehensive time-resolved ESI-MS analysis, yielding unprecedented mechanistic information regarding the initial interactions and reorganizations of the {γ-SiW10} precursor in the presence of Fe2+.
A mononuclear FeII complex, prepared with a Brønsted diacid ligand, H2L (H2L=2‐5‐phenyl‐1H‐pyrazole‐3‐yl 6‐benzimidazole pyridine), shows switchable physical properties and was isolated in five ...different electronic states. The spin crossover (SCO) complex, FeII(H2L)2(BF4)2 (1A), exhibits abrupt spin transition at T1/2=258 K, and treatment with base yields a deprotonated analogue FeII(HL)2 (1B), which shows gradual SCO above 350 K. A range of FeIII analogues were also characterized. FeIII(HL)(H2L)(BF4)Cl (1C) has an S=5/2 spin state, while the deprotonated complexes FeIII(L)(HL), (1D), and (TEA)FeIII(L)2, (1E) exist in the low‐spin S=1/2 state. The electronic properties of the five complexes were fully characterized and we demonstrate in situ switching between multiple states in both solution and the solid‐state. The versatility of this simple mononuclear system illustrates how proton donor/acceptor ligands can vastly increase the range of accessible states in switchable molecular devices.
Switch that: A mononuclear FeII complex prepared with an asymmetric Brønsted ligand exhibited multi‐state switchable properties and was isolated in five distinct electronic states. By modifying the degree of protonation, both spin‐ and redox‐interconversion was observed, resulting in a range of tunable magnetic, electrochemical, and optical properties. SCO=spin crossover.
A TTF‐based (TTF=tetrathiafulvalene) tridentate ligand (α‐(4′‐methyl‐4,5‐di‐n‐dodecylthylthiotetrathiafulvalene‐5′‐ylthio)‐ α′‐2,2,2‐tris(1‐pyrazolyl)ethoxy‐p‐xylene) (L) with long‐chain alkyl ...moieties was prepared in order to obtain a new multi‐redox active gelator based on a mixed‐metal octanuclear complex FeIII4NiII4(CN)12(tp)4(L)4(BF4)4 (1). The magnetism, electrochemistry, and gelation behavior of 1 were studied and 1,2‐dichlorobenzene solutions of 1 are shown to display thermoreversible gelation behavior at room temperature. Furthermore, the gel phase of 1 was shown to undergo room‐temperature gel‐to‐sol transformations induced by both the oxidation and reduction of the gelator complex by F4TCNQ or FeII(Cp*)2, respectively.
A new heterometallic, discrete metallogelator based on an octanuclear cyanometallate {Fe4Ni4} complex, supported by long‐chain alkyl ligands with incorporated tetrathiafulvalene moieties, was synthesized. It exhibited thermoreversible gelation behavior at room temperature and redox‐mediated gel‐to‐sol transitions.
This study explores a new method to maximize the visible-light-driven photocatalytic performance of organic–inorganic hybrid polyoxometalates (POMs). Experimental and theoretical investigations of a ...family of phosphonate-substituted POMs show that modification of grafted organic moieties can be used to tune the electronic structure and photoactivity of the metal oxide component. Unlike fully inorganic polyoxotungstates, these organic–inorganic hybrid species are responsive to visible light and function as photocatalysts (λ > 420 nm) in the decomposition of a model environmental pollutant. The degree of photoactivation is shown to be dependent on the nature of the inductive effect exerted by the covalently grafted substituent groups. This study emphasizes the untapped potential that lies in an orbital engineering approach to hybrid-POM design and helps to underpin the next generation of bespoke, robust, and cost-effective molecular metal oxide photoactive materials and catalysts.
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