CO2 coordination by inorganic polyoxoanion in water

Research on the Construction of a Series of Transition Metal-Substituted Keggin-Type TMSPOMs@PCN-224 Composites through the Encapsulation Method and Their Electron Transfer Mechanism in CO2RR

In order to take advantage of the distinct reversible multielectron transfer properties of polyoxometalates (POMs) and increase the electron density at the active sites during the electrochemical reduction of CO2 (CO2RR), a range of transition metal-doped polyoxometalates (TMSPOMs) was entrapped within the porphyrin-based framework of PCN-224 via an encapsulation method, known as TMSPOMs@PCN-224 (TMSPOMs = [XW11O39MII(H2O)]n-, [XW11O40VIV]n-, M = CoII, MnII; X = Si, n = 6; X = P, n = 5). The central elements (Si, P) and the incorporated transition metals (VIV, CoII, and MnII) both play a role in adjusting the electronic structure and electron transfer during the CO2RR process. Remarkably, the composite material with cobalt substitution displayed significantly improved performance. Through fine-tuning the POM loading, the electrocatalytic activity was optimized, leading to an impressive Faradaic efficiency for CO production (FECO) of 89.9% for SiW11Co@PCN-224, a significant improvement compared to the 12.1% FECO of PCN-224. Furthermore, the electrochemical stability of this catalyst was demonstrated over 20 h. Comparative analyses involving six composite materials indicated a relationship between the negative charge of the polyanions and their ability to facilitate effective electron transfer, ultimately enhancing the catalyst's performance. Meanwhile, these findings were supported by density functional theory (DFT) calculations.

Bifunctional K3PW12O40/Graphene Oxide-Modified Separator for Inhibiting Polysulfide Diffusion and Stabilizing Lithium Anode

Lithium-sulfur (Li-S) batteries are considered as promising candidates for next-generation batteries due to their high theoretical energy density. However, the practical application of Li-S batteries is still hindered by several challenges, such as the polysulfide shuttle and the growth of lithium dendrites. Herein, we introduce a bifunctional K3PW12O40/graphene oxide-modified polypropylene separator (KPW/GO/PP) as a highly effective solution for mitigating polysulfide diffusion and protecting the lithium anode in Li-S batteries. By incorporating KPW into a densely stacked nanostructured graphene oxide (GO) barrier membrane, we synergistically capture and rapidly convert lithium polysulfides (LiPSs) electrochemically, thus effectively suppressing the shuttling effect. Moreover, the KPW/GO/PP separator can stabilize the lithium metal anode during cycling, suppress dendrite formation, and ensure a smooth and dense lithium metal surface, owing to regulated Li+ flux and uniform Li nucleation. Consequently, the constructed KPW/GO/PP separator delivered a favorable initial specific capacity (1006 mAh g-1) and remarkable cycling performance at 1.0 C (626 mAh g-1 for up to 500 cycles with a decay rate of 0.075% per cycle).

Selective electrochemical CO2 conversion with a hybrid polyoxometalate

A multi-component coordination compound, in which ruthenium antenna complexes are connected to a polyoxotungstate core is presented. This hybrid cluster effectively promotes the electrochemical conversion of CO2 to C1 feedstocks, the selectivity of which can be controlled by the acidity of the media.

First Organic–Inorganic Hybrid Compounds Formed by Ge-V-O Clusters and Transition Metal Complexes of Aromatic Organic Ligands

Three compounds based on Ge-V-O clusters were hydrothermally synthesized and characterized by IR, UV-Vis, XRD, ESR, elemental analysis and X-ray crystal structural analysis. Both [Cd(phen)(en)]2[Cd2(phen)2V12O40Ge8(OH)8(H2O)]∙12.5H2O (1) and [Cd(DETA)]2[Cd(DETA)2]0.5[Cd2(phen)2V12O41Ge8(OH)7(0.5H2O)]∙7.5H2O (2) (1,10-phen = 1,10-phenanthroline, en = ethylenediamine, DETA = diethylenetriamine) are the first Ge-V-O cluster compounds containing aromatic organic ligands. Compound 1 is the first dimer of Ge-V-O clusters, which is linked by a double bridge of two [Cd(phen)(en)]2+. Compound 2 exhibits an unprecedented 1-D chain structure formed by Ge-V-O clusters and [Cd2(DETA)2]4+ transition metal complexes (TMCs). [Cd(en)3]{[Cd(η2-en)2]3[Cd(η2-en)(η2-μ2-en)(η2-en)Cd][Ge6V15O48(H2O)]}∙5.5H2O (3) is a novel 3-D structure which is constructed from [Ge6V15O48(H2O)]12− and four different types of TMCs. We also synthesized [Zn2(enMe)3][Zn(enMe)]2[Zn(enMe)2(H2O)]2[Ge6V15O48(H2O)]∙3H2O (4) and [Cd(en)2]2{H8[Cd(en)]2Ge8V12O48(H2O)}∙6H2O (5) (enMe = 1,2-propanediamine), which have been reported previously. In addition, the catalytic properties of these five compounds for styrene epoxidation have been assessed.

A Keggin-type polyoxomolybdate-based crystalline material formed by hydrothermal transformation: photo/electro-catalytic properties and mechanism study

This study constructs a POM-based crystalline material of [(SiMo12O40)Cu6(2,2′-bipy)6(Mo6O22)] (1). The photocatalytic MB degradation and electrocatalytic nitrite reduction properties of complex 1 are systematically studied for the first time.

One-Pot, Room-Temperature Conversion of CO2 into Porous Metal-Organic Frameworks

The conversion of CO₂ into functional materials under ambient conditions is a major challenge to realize a carbon-neutral society. Metal-organic frameworks (MOFs) have been extensively studied as designable porous materials. Despite the fact that CO₂ is an attractive renewable resource, the synthesis of MOFs from CO₂ remains unexplored. Chemical inertness of CO₂ has hampered its conversion into typical MOF linkers such as carboxylates without high energy reactants and/or harsh conditions. Here, we present a one-pot conversion of CO₂ into highly porous crystalline MOFs at ambient temperature and pressure. Cubic [Zn₄O(piperazine dicarbamate)₃] is synthesized via in situ formation of bridging dicarbamate linkers from piperazines and CO₂ and shows high surface areas (∼2366 m² g^-1) and CO₂ contents (>30 wt %). Whereas the dicarbamate linkers are thermodynamically unstable by themselves and readily release CO₂, the formation of an extended coordination network in the MOF lattices stabilizes the linker enough to demonstrate stable permanent porosity.

Self-Assembled Polyoxometalate Nanodots as Bidirectional Cluster Catalysts for Polysulfide/Sulfide Redox Conversion in Lithium-Sulfur Batteries

Polyoxometalates (POMs) are a class of discrete molecular inorganic metal-oxide clusters with reversible multielectron redox capability. Taking advantage of their redox properties, POMs are thus expected to be directly involved in the lithium-sulfur batteries (Li-S, LSBs) system as a bidirectional molecular catalyst. Herein, we design a three-dimensional porous structure of reduced graphene-carbon nanotube skeleton supported POM catalyst as a high-conductive and high-stability host material. Based on various spectroscopic techniques and in situ electrochemical studies together with computational methods, the catalytic mechanism of POM clusters in Li-S battery was systematically clarified at the molecular level. The constructed POM-based sulfur cathode delivers a reversible capacity 1110 mAh g^-1 at 1.0 C and cycling stability up to 1000 cycles at 3.0 C. Furthermore, Li-S pouch/beaker batteries with a POM-based cathode were successfully demonstrated. This work provides essential inputs to promote molecular catalyst design and its application in LSBs.

Transition Metal Complexes as Catalysts for the Electroconversion of CO2 : An Organometallic Perspective

The electrocatalytic transformation of carbon dioxide has been a topic of interest in the field of CO2 utilization for a long time. Recently, the area has seen increasing dynamics as an alternative strategy to catalytic hydrogenation for CO2 reduction. While many studies focus on the direct electron transfer to the CO2 molecule at the electrode material, molecular transition metal complexes in solution offer the possibility to act as catalysts for the electron transfer. C1 compounds such as carbon monoxide, formate, and methanol are often targeted as the main products, but more elaborate transformations are also possible within the coordination sphere of the metal center. This perspective article will cover selected examples to illustrate and categorize the currently favored mechanisms for the electrochemically induced transformation of CO2 promoted by homogeneous transition metal complexes. The insights will be corroborated with the concepts and elementary steps of organometallic catalysis to derive potential strategies to broaden the molecular diversity of possible products.

Inorganic–organic hybrid supramolecular architectures based on Keggin polyoxometalates and crown ether: synthesis, crystal structure and electrochemical properties

Novel supramolecular assemblies built from Keggin-type polyoxometalate and [18]-crown-6 ether building blocks exhibit unique propeller-like supramolecular host–guest structures.

Self-Assembled Supramolecular Polyoxometalate Hybrid Architecture as a Multifunctional Oxidation Catalyst

Polyoxometalates (POMs) are widely applied as tuneable and versatile catalysts for a variety of oxidation reactions in an aqueous/organic two-phase system. However, the practical applications of POMs-based biphasic catalysis are hampered by low space-time yields and mass-transport limitation between two layers due to extremely low solubility of the organic reactants in the aqueous phase. Here, we first introduced β-cyclodextrin (β-CD) as an inverse phase transfer agent and a supramolecular nanoreactor to construct a supramolecular POM inorganic-organic hybrid framework (KCl₄)Na₇[(β-CD)₃(SiW₁₂O₄₀)]·9H₂O {3CD@SiW₁₂} for various oxidation catalyses. In contrast to free CD, Keggin [SiW₁₂O₄₀]^4- catalysts, and their mixture, the {3CD@SiW₁₂} catalyst, efficiently catalyze oxidation reactions of alcohol, alkene, and thiophene. A comprehensive strategy of experimental, crystallographic, and density functional theory (DFT) calculations elucidates that the catalytic pathway involved three combined aspects of supramolecular recognition, phase transfer property, and POM catalysis. The strategic combination of supramolecular characteristic and POM-based catalysts to fabricate supramolecular POM hybrid materials opens up new economic and green tuning options, thus paving the way to informed catalyst design.

A "directed precursor self-assembly" strategy for the facile synthesis of heteropoly blues: crystal structures, formation mechanism and electron distribution

Recent research studies demonstrated that heteropoly blues (reduced polyoxometalates) could act as a special kind of solid material with potential functions in antiviral activity, and photocatalytic, photothermal and semiconducting properties. In this work, we develop a "directed precursor self-assembly" strategy for the facile synthesis of heteropoly blues (HPBs), so four representative HPBs [GeW₁₀MoO₄₀], [GeMoMoO₄₀], [P₂W₁₆MoO₆₂] and [P₂W₁₂MoMoO₆₂] have been synthesized and structurally characterized. These four heteropoly blue compounds were synthesized by the solution self-assembly reaction of a precursor [MoO₄(H₂O)₂(ox)₂]^2- with vacant polyoxometalates. Electrospray ionization mass spectrometry (ESI-MS) was used to analyze the assembly mechanism of these HPBs. A detailed study on the magnetic properties was also carried out, which shows that the number of Mo^V and their locations are capable of adjusting the electron distribution in HPBs.

Pathways towards true catalysts: computational modelling and structural transformations of Zn-polyoxotungstates

Current catalysis undergoes a paradigm shift from molecular and heterogeneous realms towards new dynamic catalyst concepts. This calls for innovative strategies to understand the essential catalytic motifs and true catalysts emerging from oxidative transformation processes. Polyoxometalate (POM) clusters offer an inexhaustible reservoir for new noble metal-free catalysts and excellent model systems whose structure-activity relationships and mechanisms remain to be explored. Here, we first introduce a new {Zn_nNa_6-n(B-α-SbW₉O₃₃)₂} (n = 3-6) catalyst family with remarkable tuning options of the Zn-based core structure and high activity in H₂O₂-assisted catalytic alcohol oxidation as a representative reaction. Next, high level solution-based computational modelling of the intermediates and transition states was carried out for [Zn₆Cl₆(SbW₉O₃₃)₂]^12- as a representative well-defined case. The results indicate a radical-based oxidation process with the involvement of tungsten and adjacent zinc metal centers. The {Zn_nNa_6-n(B-α-SbW₉O₃₃)₂} series indeed efficiently catalyses alcohol oxidation via peroxotungstate intermediates, in agreement with strong spectroscopic support and other experimental evidence for the radical mechanism. Finally, the high performance of [Zn₆Cl₆(SbW₉O₃₃)₂]^12- was traced back to its transformation into a highly active and robust disordered Zn/W-POM catalyst. The atomic short-range structure of this resting pre-catalyst was elucidated by RMC modelling of the experimental W-L₃ and Zn-K edge EXAFS spectra and supported with further analytical methods. We demonstrate that computational identification of the reactive sites combined with the analytical tracking of their dynamic transformations provides essential input to expedite cluster-based molecular catalyst design.

Polyoxometalate-Based Catalysts for CO2 Conversion

Polyoxometalates (POMs) are a diverse class of anionic metal-oxo clusters with intriguing chemical and physical properties. Owing to unrivaled versatility and structural variation, POMs have been extensively utilized for catalysis for a plethora of reactions. In this focused review, the applications of POMs as promising catalysts or co-catalysts for CO₂ conversion, including CO₂ photo/electro reduction and CO₂ as a carbonyl source for the carbonylation process are summarized. A brief perspective on the potentiality in this field is proposed.

Polyoxometalates in photocatalysis

Recent developments in polyoxometalate photochemistry are discussed with a focus on visible light driven productive chemical reactions. Special attention is given to the fundamental photochemistry of polyoxometalates and the effects on the resulting photoprocesses.

Carbonate encapsulation from dissolved atmospheric CO2 into a polyoxovanadate capsule

A fully reduced polyoxovanadate compound [Na₆(H₂O)₂₄][H₈VIV15O₃₆(CO₃)]·3N₂H₄·10H₂O (1) with CO₃²⁻ encapsulation in its internal cavity (from dissolved aerial CO₂ in the synthesis reaction mixture) is reported. Compound 1 crystals, on exposure of HCl vapor, excludes carbonate as a CO₂ gas that can be reacted with a Grignard reagent to produce triphenylcarbinol as a major product.

Visible-light CO2 photoreduction of polyoxometalate-based hybrids with different cobalt clusters

Two novel high-nuclear cobalt-based polyoxometalates can effectively improve photocatalytic activities for CO₂ photoreduction under visible light.

A rare three-dimensional POM-based inorganic metal polymer bonded by CO2 with high catalytic performance for CO2 cycloaddition

A rare inorganic framework constructed from CO₂ and polyoxoanions exhibits interesting performance in the cycloaddition of CO₂ with epoxides.

Polyoxometalate-encapsulated twenty-nuclear silver-tetrazole nanocage frameworks as highly active electrocatalysts for the hydrogen evolution reaction

Two unprecedented polyoxometalate (POM)-encapsulated twenty-nuclear silver-tetrazole nanocage frameworks have been successfully synthesized, which exhibit high activity in the hydrogen evolution reaction.

A new polyoxovanadate-based metal–organic framework: synthesis, structure and photo-/electro-catalytic properties

A new polyoxovanadate-based metal–organic framework has been synthesized, which exhibits high-performance bifunctional photo-/electro-catalytic properties.

Oxidative Polyoxometalates Modified Graphitic Carbon Nitride for Visible-Light CO2 Reduction

Developing a photocatalysis system for converting CO₂ to valuable fuels or chemicals is a promising strategy to address global warming and fossil fuel consumption. Exploring photocatalysts with high-performance and low-cost has been two ultimate goals toward photoreduction of CO₂. Herein, noble-metal-free polyoxometalates (Co4) with oxidative ability was first introduced into g-C₃N₄ resulted in inexpensive hybrid materials (Co4@g-C₃N₄) with staggered band alignment. The staggered composited materials show a higher activity of CO₂ reduction than bare g-C₃N₄. An optimized Co4@g-C₃N₄ hybrid sample exhibited a high yield (107 μmol g^-1 h^-1) under visible-light irradiation (λ ≥ 420 nm), meanwhile maintaining high selectivity for CO production (94%). After 10 h of irradiation, the production of CO reached 896 μmol g^-1. Mechanistic studies revealed the introduction of Co4 not only facilitate the charge transfer of g-C₃N₄ but greatly increased the surface catalytic oxidative ability. This work creatively combined g-C₃N₄ with oxidative polyoxometalates which provide novel insights into the design of low-cost photocatalytic materials for CO₂ reduction.

A new type of photomagnetic system: photoinduced charge transfer in polyoxometalate-based organic-inorganic hybrid

Herein, we show a new photomagnetic system that gives rise to the magnetic transformation from diamagnetism to paramagnetism by photoinduced intramolecular charge transfer in the polyoxometalate-based organic-inorganic hybrid, [(VMo6O22)2{O2C(CH2)2CO2}3] (1).

New organic–inorganic hybrid compounds constructed from polyoxometalates and transition metal mixed-organic-ligand complexes

Five compounds constructed from different polyoxoanions and metal mixed-organic complexes of carboxylates and nitrogen-containing ligands have been synthesized and characterized.

Multicomponent self-assembly of a pentanuclear Ir–Zn heterometal–organic polyhedron for carbon dioxide fixation and sulfite sequestration

An iridium-containing pentanuclear metal–organic polyhedron was constructedviaa subcomponent self-assembly. The three equatorial Zn(ii) ions in the structure induced atmospheric carbon dioxide transformation as carbonate and sulfur dioxide as sulfite with bonding to the three metal centers.

A Dimetalloxycarbene Bonding Mode and Reductive Coupling Mechanism for Oxalate Formation from CO2

We describe the stable and isolable dimetalloxycarbene [(TiX3 )2 (μ2 -CO2 -κ(2) C,O:κO')] 5, where X=N-(tert-butyl)-3,5-dimethylanilide, which is stabilized by fluctuating μ2 -κ(2) C,O:κ(1) O' coordination of the carbene carbon to both titanium centers of the dinuclear complex 5, as shown by variable-temperature NMR studies. Quantum chemical calculations on the unmodified molecule indicated a higher energy of only +10.5 kJ mol(-1) for the μ2 -κ(1) O:κ(1) O' bonding mode of the free dimetalloxycarbene compared to the μ2 -κ(2) C,O:κ(1) O' bonding mode of the masked dimetalloxycarbene. The parent cationic bridging formate complex [(TiX3 )2 (μ2 -OCHO-κO:κO')][B(C6 F5)4], 4[B(C6 F5)4], was simply deprotonated with the strong base K(N(SiMe3 )2 ) to give 5. Complex 5 reacts smoothly with CO2 to generate the bridging oxalate complex [(TiX3 )2 (μ2 -C2 O4 -κO:κO'')], 6, in a C-C bond formation reaction commonly anticipated for oxalate formation by reductive coupling of CO2 on low-valent transition-metal complexes.

An unprecedented 3D POM–MOF based on (7,8)-connected twin Wells–Dawson clusters: synthesis, structure, electrocatalytic and photocatalytic properties

The first (7,8)-connected POM–MOF has been obtained, representing the highest connected POMs to any mixed-connected POM–MOF and a unique structure that contains organic–inorganic and all-inorganic networks.