The formulation of advanced molecular materials with bespoke polymeric ionic‐liquid matrices that stabilize and solubilize hybrid organic–inorganic polyoxometalates and allow their processing by ...additive manufacturing, is effectively demonstrated. The unique photo and redox properties of nanostructured polyoxometalates are translated across the scales (from molecular design to functional materials) to yield macroscopic functional devices with reversible photochromism. These properties open a range of potential applications including reversible information storage based on controlled topological and temporal reduction/oxidation of pre‐formed printed devices. This approach pushes the boundaries of 3D printing to the molecular limits, allowing the freedom of design enabled by 3D printing to be coupled with the molecular tuneability of polymerizable ionic liquids and the photoactivity and orbital engineering possible with hybrid polyoxometalates.
Novel reversible photochromic materials consisting of bespoke poly(ionic liquid) matrices and hybrid organic–inorganic polyoxometalates are presented. The unique photoredox properties of nanostructured polyoxometalates are translated across the size scales to yield macroscopic functional photochromic devices. The freedom afforded by 3D printing is coupled with the molecular tuneability of poly(ionic liquids) and the photoactivity and orbital engineering enabled by hybrid polyoxometalates.
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.
This perspective reviews our recent efforts towards the self-assembly of polynuclear clusters with ditopic and tritopic multidentate ligands HL
1
...(2-phenyl-4,5-bis{6-(3,5-dimethylpyrazol-1-yl)pyrid-2-yl}-1
H
-imidazole) and H
2
L
2
(2,6-bis-5-(2-pyridinyl)-1
H
-pyrazole-3-ylpyridine), both of which are planar and rigid molecules. HL
1
was found to be an excellent support for tetranuclear Fe
4
complexes, Fe
II
4
(L
1
)
4
(BF
4
)
4
(Fe
II
4
) and Fe
III
2
Fe
II
2
(L
1
)
4
(BF
4
)
6
(Fe
III
2
Fe
II
2
). The homovalent system was found to exhibit multistep spin crossover (SCO), while the mixed-valence Fe
III
2
Fe
II
2
complex shows wavelength-dependent tuneable light-induced excited spin state trapping (LIESST). For H
2
L
2
, a variety of polynuclear complexes were obtained through complexation with different transition metal ions, allowing the isolation of rings, grids, and helix structures. The rigidity of the ligand, difference in its coordination sites, and affinity for different metal ions dictates its coordination behaviour. In this paper, we summarise these ligand pre-programmed self-assembled clusters and their diverse physical properties.
This perspective reviews our recent efforts towards the self-assembly of polynuclear clusters with ditopic and tritopic multidentate ligands HL
1
(2-phenyl-4,5-bis{6-(3,5-dimethylpyrazol-1-yl)pyrid-2-yl}-1
H
-imidazole) and H
2
L
2
(2,6-bis-5-(2-pyridinyl)-1
H
-pyrazole-3-ylpyridine), both of which are planar and rigid molecules.
Bistable compounds that exist in two interchangeable phases under identical conditions can act as switches under external stimuli. Among such switchable materials, coordination complexes have energy ...levels (or phases) that are determined by the electronic states of their constituent metal ions and ligands. They can exhibit multiple bistabilities and hold promise in the search for multifaceted materials that display different properties in different phases, accessible through the application of contrasting external stimuli. Molecular systems that exhibit both thermo- and photoinduced magnetic bistabilities are excellent candidates for such systems. Here we describe a cyanide-bridged CoFe one-dimensional chiral coordination polymer that displays both magnetic and electric bistabilities in the same temperature range. Both the electric and magnetic switching probably arise from the same electron-transfer coupled spin-transition phenomenon, which enables the reversible conversion between an insulating diamagnetic phase and either a semiconducting paramagnetic (thermoinduced) or a type of ferromagnetic single-chain magnet (photoinduced) state.
Photo-switchable systems, such as discrete spin-crossover complexes and bulk iron-cobalt Prussian blue analogues, exhibit, at a given temperature, a bistability between low- and high-spin states, ...allowing the storage of binary data. Grouping different bistable chromophores in a molecular framework was postulated to generate a complex that could be site-selectively excited to access multiple electronic states under identical conditions. Here we report the synthesis and the thermal and light-induced phase transitions of a tetranuclear iron(II) grid-like complex and its two-electron oxidized equivalent. The heterovalent grid is thermally inactive but the spin states of its constituent metal ions are selectively switched using different laser stimuli, allowing the molecule to exist in three discrete phases. Site-selective photo-excitation, herein enabling one molecule to process ternary data, may have major ramifications in the development of future molecular memory storage technologies.
The development of next‐generation molecular‐electronic, electrocatalytic, and energy‐storage systems depends on the availability of robust materials in which molecular charge‐storage sites and ...conductive hosts are in intimate contact. It is shown here that electron transfer from single‐walled carbon nanotubes (SWNTs) to polyoxometalate (POM) clusters results in the spontaneous formation of host–guest POM@SWNT redox‐active hybrid materials. The SWNTs can conduct charge to and from the encapsulated guest molecules, allowing electrical access to >90% of the encapsulated redox species. Furthermore, the SWNT hosts provide a physical barrier, protecting the POMs from chemical degradation during charging/discharging and facilitating efficient electron transfer throughout the composite, even in electrolytes that usually destroy POMs.
Reagent‐free redox‐driven nanoconfinement of polyoxometalate clusters within single‐walled carbon nanotubes is demonstrated. The densely packed chains of the polyoxometalate (POM) anions within cationic single‐walled carbon nanotubes form spontaneously and irreversibly under ambient conditions. Protected from the external environment and effectively “wired” to the carbon support, the nanoconfined redox‐active POMs exhibit exceptional electrochemical stability, even in environments in which they cannot usually exist.
A mixed-valence heterometallic nonanuclear 3 × 3 grid complex, CuI 2CuII 6FeIII(L)6(BF4)5·MeOH·9H2O (1; MeOH = methanol), was synthesized by a one-pot reaction of copper and iron ions with ...multidentate ligand 2,6-bis5-(2-pyridinyl)-1H-pyrazol-3-ylpyridine (H2L). 1 showed five quasi-reversible one-electron redox processes centered at +0.74, +0.60, +0.39, +0.27, and −0.13 V versus SCE, assignable to four CuI/CuII processes and one FeII/FeIII couple, respectively. The two-electron-oxidized species CuII 8FeIII(L)6(PF6)7·4MeOH·7H2O (1 2eOx ), the two-electron-reduced species CuI 4CuII 4FeIII(L)6(PF6)3·2H2O (1 2eRed ), and the three-electron-reduced species CuI 4CuII 4FeII(L)6(PF6)2·5MeOH·H2O (1 3eRed ) were isolated electrochemically. The four redox isomers were characterized by single-crystal X-ray analysis, SQUID magnetometry, and Mössbauer spectroscopy.
We describe the preparation of hybrid redox materials based on polyoxomolybdates encapsulated within single‐walled carbon nanotubes (SWNTs). Polyoxomolybdates readily oxidize SWNTs under ambient ...conditions in solution, and here we study their charge‐transfer interactions with SWNTs to provide detailed mechanistic insights into the redox‐driven encapsulation of these and similar nanoclusters. We are able to correlate the relative redox potentials of the encapsulated clusters with the level of SWNT oxidation in the resultant hybrid materials and use this to show that precise redox tuning is a necessary requirement for successful encapsulation. The host–guest redox materials described here exhibit exceptional electrochemical stability, retaining up to 86 % of their charge capacity over 1000 oxidation/reduction cycles, despite the typical lability and solution‐phase electrochemical instability of the polyoxomolybdates we have explored. Our findings illustrate the broad applicability of the redox‐driven encapsulation approach to the design and fabrication of tunable, highly conductive, ultra‐stable nanoconfined energy materials.
The wide applicability of the redox‐driven encapsulation of polyoxometalates (POMs) within single‐walled carbon nanotubes is shown, demonstrating that the level of carbon oxidation and the efficacy of the filling are determined by the frontier orbital energies of the POM. Nanoencapsulation is found to confer significant stability to polyoxomolybdates despite their inherent lability.
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.
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